Patterns of climate change across Scotland: technical report - Sniffer

Final Report 

Project CC03 

Patterns of climate change across Scotland: technical report 

May 2006

© Crown Copyright, Met Office 2006 

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servants or agents accept no liability whatsoever for any loss or damage arising from the 

interpolation or use of the information, or reliance upon views contained herein. 

Dissemination status 

Unrestricted 

Research contractor 

This document was produced by: 

Claire Barnett and Matthew Perry 

Met Office, FitzRoy Road, 

Exeter, Devon, EX1 3PB, 

United Kingdom 

Jo Hossell, Greg Hughes and Chris Procter 

Woodthorne, Wergs Road 

Wolverhampton, WV6 8TQ 

United Kingdom 

The report should be referenced as: 

Barnett, C., J. Hossell, M. Perry, C. Procter and G. Hughes (2006) Patterns of climate change 

across Scotland: Technical Report. SNIFFER Project CC03, Scotland & Northern Ireland Forum 

for Environmental Research, 102pp. 

SNIFFER’s project manager 

SNIFFER’s project manager for this contract is: 

Noranne Ellis, Scottish Natural Heritage 

SNIFFER’s project steering group members are: 

June Graham, Scottish Environment Protection Agency (SEPA) 

Helen McKay, Forestry Commission 

Peter Singleton, Scottish Environment Protection Agency (SEPA) 

Guy Winter, Scottish Executive 

SNIFFER 

First Floor, Greenside House, 25 Greenside Place, EDINBURGH EH1 3AA 

Company No: SC149513 

Scottish Charity: SCO22375 

www.sniffer.org.uk

EXECUTIVE SUMMARY 

CC03: Patterns of climate change across Scotland, March 2006 

Project funders/partners: Scotland and Northern Ireland Forum for Environmental Research 

(SNIFFER), Scottish Executive, Scottish Environment Protection Agency (SEPA), Scottish 

Natural Heritage (SNH) and the Forestry Commission. 

Background to research 

The Scottish mainland and Scottish Isles warmed by 0.69°C and 0.64°C respectively, over the 

period 1861-2000 (Jones and Lister, 2004). Precipitation patterns have also altered, generally 

producing drier summer and wetter winters but there has also been an increased frequency of 

heavy rain events (Mayes, 1996; Smith, 1995). Generalised annual values at a national level 

can mask significant regional and seasonal variations. In order to plan for adaptation to climate 

change there is a need to know the degree of change in specific locations across the seasons. 

Only then can potential future trends for that locality be considered in the context of the latest 

UK Climate Impacts Programme (UKCIP) climate change scenarios. 

Objectives of research 

The aim of this study is to collate records of observed data in order to provide an up to date 

assessment of how the climate of Scotland has changed, not just giving a nationally averaged 

result but identifying regional patterns of change. This study provides a benchmark against 

which future change can be measured. The analysis of trends shows how far Scotland’s climate 

has altered. It also places the predicted future climate of Scotland within the context of changes 

already observed. It thereby provides information essential to those considering the need to 

adapt to the impacts of climate change in Scotland. A stakeholder survey was conducted in 

order to ensure the capture of key variables. The findings of the study are presented in 

summary form as a Handbook, with the full details of the analysis being given in this technical 

handbook. 

When descriptions of our changing climate are presented in terms of nationally averaged annual 

mean statistics, significant regional and seasonal variations can be masked. This technical 

report describes the analysis of a number of high-resolution datasets. These are based upon 

data from a dense network of observing stations that has been gridded using some of the latest 

data regression and interpolation techniques. The datasets include temperature and 

precipitation from 1914 to 2004, sunshine from 1929 to 2004, and a range of other variables, 

such as mean sea level and snow cover, from 1961. A number of quantities based upon either 

temperature or rainfall, such as growing season length and rainfall intensity, have also been 

derived. These datasets have been analysed in order to identify patterns of change in the 

Scottish climate over time and space. 

Key findings 

• Since 1914 average temperatures in Scotland have risen by 0.5°C. Northern Scotland has 

warmed at a slower rate than the rest of the country, with average increases in temperature only 

being significant in spring. In northern Scotland, there has been little change in winter 

temperatures since 1914. 

• Temperatures have increased in every season and in all parts of Scotland since 1961. This 

has been the fastest period of warming observed over the 1914 to 2004 period analysed in this 

i

study. Since 1961 average spring, summer and winter temperatures have risen by more than 

1°C. 

• Since 1961 average daily maximum temperatures have been increasing at a faster rate than 

average minimum, or night time, temperatures in Scotland. Globally, over approximately the 

same period, it is minimum temperatures that have increased at the faster rate. It is interesting 

to note that conversely the trend in Scotland over the 1914 to 2004 period also has the 

minimum temperatures increasing at the faster rate. 

• Scotland has become wetter since 1961, with an average increase of almost sixty percent in 

winter months in northern and western Scotland. For the majority of the country there has not 

been a large-scale significant change in average summer rainfall although some parts of north 

west Scotland have become up to forty five percent drier in summer. Contrary to the Scottish 

national trend, Aberdeenshire has seen little change in precipitation in winter months although 

this is compensated for in this region by a significant increase in precipitation in autumn 

(September-November). 

• Heavy rainfall events have increased significantly in winter, particularly in northern and 

western regions. 

• The snow season has shortened across the country since 1961, with the season starting 

later and finishing earlier in the year. The greatest reductions have occurred in northern and 

western Scotland. 

• Since 1961 there has been more than a twenty-five percent reduction in the number of days 

of frost (both air and ground frost) across the country. At the same time, the growing season 

length has increased significantly, with the greatest change occurring at the beginning of the 

season. 

• Inconsistent methods for observing cloud data and the challenges of analysing wind 

observations have meant that identification of any trends or patterns of change in these 

quantities has not been possible in this study. Further, more complex, data analysis techniques 

would be required for such an undertaking. 

• The majority of the analysis presented here is based upon data for 1961 to 2004. Longer 

data records for temperature and precipitation have allowed trends over this time to be put into 

the context of a long period. The study highlights the fact that since 1961 both annual mean 

temperature and precipitation have increased at a faster rate than at any other time in the ninety 

years considered. 

• The trends identified since 1961 are not always consistent with those that might be expected 

based upon the future climate of Scotland projected by climate models, although evidence of 

such trends often exists in the longer record, i.e. the 1914 to 2004 dataset. This underlines the 

fact that caution is required when drawing conclusions about trends and climate change based 

upon a relatively short data period. 

This study is focused upon the identification of trends in Scottish climate and providing the 

regional and spatial detail that national averages mask. The study does not seek to explain, or 

attribute a cause, for identified trends. Although some of the trends identified are consistent with 

projected future climate for Scotland, it is not possible to say that the trends are evidence of 

man-made, i.e. anthropogenic, climate change. However, many of the trends identified are 

significant and therefore beyond the range expected from natural variability. Whether or not the 

changes are due to anthropogenic climate change it is clear that these observed trends are 

often comparable with those predicted for the future. This means that Scotland already has 

experience of the impact of such changes and is therefore well placed to plan the necessary 

adaptation measures for the future. 

Key words: Scotland, climate change, observed trends 

ii

SNIFFER Project CC03: Patterns of climate change across Scotland: technical report May 2006 

TABLE OF CONTENTS 

EXECUTIVE SUMMARY ...............................................................................................................i 

1. INTRODUCTION...................................................................................................................1 

2. OBSERVED TRENDS IN SCOTTISH CLIMATE .................................................................3 

2.1. Data analysis.................................................................................................................6 

2.2. Temperature..................................................................................................................7 

2.3. Rainfall ........................................................................................................................24 

2.4. Snow and frost ............................................................................................................34 

2.5. Sunshine .....................................................................................................................42 

2.6. Cloud...........................................................................................................................45 

2.7. Mean sea level pressure .............................................................................................46 

2.8. Wind ............................................................................................................................48 

3. PREDICTED FUTURE CHANGE IN SCOTTISH CLIMATE ..............................................51 

3.1. Observed trends in Scottish climate: the UKCIP02 context ........................................51 

3.1.1 Temperature................................................................................................................51 

3.1.2 Precipitation.................................................................................................................52 

3.1.3 Snowfall.......................................................................................................................53 

3.1.4 Sunshine .....................................................................................................................53 

3.1.5 Mean sea level pressure .............................................................................................53 

3.1.6 Wind ............................................................................................................................53 

4. CONCLUSIONS..................................................................................................................55 

5. REFERENCES....................................................................................................................57 

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List of Tables 

Table 1 Average number of stations included per month in the gridded dataset. 5 

Table 2 Mean temperature changes (°C), 1961 to 2004 and 1914 to 2004 8 

Table 3 24-hour maximum temperature changes (°C), 1961 to 2004 and 1914 to 2004 10 

Table 4 24-hour minimum temperature changes (°C), 1961 to 2004 and 1914 to 2004 10 

Table 5 Mean diurnal temperature range changes (°C), 1961 to 2004 13 

Table 6 Changes in annual temperature indices, 1961 to 2004: (a) heating degree 15 

days (%), (b) growing degree days (%), (c) growing season length (days), 

and (d) extreme temperature range (°C) 

Table 7 Changes in summer and winter half-year heat and cold wave durations 22 

(days), 1961 to 2003 

Table 8 Changes in total precipitation amount (%), 1961 to 2004 and 1914 to 2004 25 

Table 9 Changes in days of heavy rain ≥ 10 mm, 1961 to 2004 28 

Table 10 Changes in annual precipitation indices, 1961 to 2004: (a) maximum 31 

consecutive dry days (days), (b) mean rainfall intensity, (c) maximum 

5-day precipitation amount (%) 

Table 11 Changes in days of snow cover (%), 1961/62 to 2004/05 24 

Table 12 Changes in days of air frost (%) 1096/62 to 2004/05 36 

Table 13 Changes in days of ground frost (%), 1961/62 to 2004/05 37 

Table 14 Changes in the dates of the first and last ground frost, 1961 to 2005 41 

Table 15 Changes in total sunshine hours (%), 1961 to 2004 and 1929 to 2004 42 

Table 16 Changes in percentage cloud cover, 1961 to 2004 45 

Table 17 Changes in mean sea level pressure (hPa), 1961 to 2004 46 

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List of Figures 

Figure 1 Location of observing sites (January 2001) for data used in the 4 

construction of the Met Office gridded datasets. 

Figure 2 Map of Scotland showing boundaries of the three regions as defined 7 

in this study (North, West and East Scotland). 

Figure 3 Annual mean temperature (°C) for Scottish regions, 1914 to 2004. 8 

Figure 4 Gridded change for mean temperature (°C), based on a linear trend from 9 

1961 to 2004 (a) spring, (b) summer, (c) autumn and (d) winter. 

Figure 5 Annual average 24-hour maximum temperature (°C) for Scottish regions, 11 

1914 to 2004 

Figure 6 Annual average 24-hour minimum temperature (°C) for Scottish regions, 11 

1914 to 2004. 

Figure 7 Gridded change for 24-hour maximum temperature (°C), based on a linear 12 

trend from 1961 to 2004 (a) summer and (b) winter. 

Figure 8 Gridded change for 24-hour minimum temperature (°C), based on a linear 13 

trend from 1961 to 2004 (a) summer and (b) winter. 

Figure 9 Annual mean diurnal temperature range (°C) for Scottish regions, 14 

1961 to 2004. 

Figure 10 Annual heating degree days for Scottish regions, 1961 to 2003. 16 

Figure 11 Annual growing degree days for Scottish regions, 1961 to 2003. 17 

Figure 12 Annual growing season length (days) for Scottish regions, 1961 to 2004 17 

Figure 13 Growing season start date for Scottish regions, 1961 to 2004. 18 

Figure 14 Growing season end date for Scottish regions, 1961 to 2004. 18 

Figure 15 Annual extreme temperature range (°C) for Scottish regions, 1961 to 2003 19 

Figure 16 Gridded change for (a) growing degree days (%) and (b) heating degree 19 

days based upon a linear trend from 1961 to 2003 

Figure 17 Gridded change for extreme temperature range (°C) based upon a linear 20 

trend from 1961 to 2003 

Figure 18 Gridded change for growing season length (days) based upon a linear 21 


Figure 19 Gridded change for (a) start and (b) end of the growing season (days) 22 

based upon a linear trend from 1961 to 2004 

Figure 20 Winter half-year cold wave duration (days) for Scottish regions, 1961/62 to 23 

2003/04. 

Figure 21 Summer half-year heat wave duration (days) for Scottish regions, 1961 to 23 

2003. 

Figure 22 Gridded change for (a) winter half-year cold wave duration (days) and 24 

(b) summer half-year heat wave duration (days) based upon a linear trend 

from 1961 to 2003 

Figure 23 Annual precipitation amount (mm) for Scottish regions, 1914 to 2004. 26 

Figure 24 Climatology of annual mean rainfall amounts (mm) for Scotland, 1961 to 2004 26 

Figure 25 Gridded change in precipitation (%), based upon a linear trend from 1961 27 

to 2004: (a) spring, (b) summer, (c) autumn, (d) winter. 

Figure 26 Annual days of heavy rain ≥10mm for Scottish regions, 1961 to 2004 28 

Figure 27 Gridded change in days of heavy rain ≥10mm, based on a linear trend 30 

from 1961 to 2004: (a) spring, (b) summer, (c) autumn, (d) winter. 

Figure 28 Annual maximum consecutive dry days for Scottish regions, 1961 to 2004 31 

Figure 29 Annual mean rainfall intensity (mm/day) for Scottish regions, 1961 to 2004 32 

Figure 30 Annual maximum 5-day precipitation amount (mm) for Scottish regions, 32 

1961 to 2004 

Figure 31 Gridded change for annual maximum consecutive dry days, based on a 33 

linear trend from 1961 to 2004 

v


Figure 32 Gridded change (%) for (a) annual rainfall intensity on days ≥1mm 34 

rainfall, and (b) annual maximum 5-day precipitation amount, based 

upon a linear trend from 1961 to 2004 

Figure 33 Climatology of number of days of snow cover for Scotland, 1961 to 1990. 35 

Spring (upper panel) and autumn (lower panel) 

Figure 34 Annual days of snow cover for Scottish regions, 1961/62 to 2004/05 36 

Figure 35 Annual days of air frost for Scottish regions, 1961/62 to 2004/05 37 

Figure 36 Annual days of ground frost for Scottish regions, 1961/62 to 2004/05 38 

Figure 37 Gridded change for (a) annual days of air frost and (b) days of snow cover, 39 

based on a linear trend from 1961 to 2004 

Figure 38 Gridded change for days of ground frost based upon a linear trend from 40 

1961 to 2004: (a) spring, (b) summer, (c) autumn and (d) winter 

Figure 39 Date of the first ground frost (in days since August 1 st ), 1960 to 2005, at 41 

four Scottish stations. 

Figure 40 Date of the last ground frost before the end of July (in days since August 1 st ), 42 

1961 to 2005, at four Scottish stations. 

Figure 41 Annual sunshine hours for Scottish regions, 1929 to 2004 43 

Figure 42 Gridded change for sunshine, based on a linear trend from 1961 to 2004: 44 

(a) spring, (b) summer, (c) autumn, (d) winter 

Figure 43 Annual percentage cloud cover for Scottish regions, 1961 to 2004 45 

Figure 44 Annual mean sea level pressure (hPa) for Scottish regions, 1961 to 2004 47 

Figure 45 Gridded change for annual average mean sea level pressure (hPa), 48 

based on a linear trend from 1961 to 2004: (a) summer, (b) winter 

Figure 46 Annual mean wind speed (knots) for three Scottish stations: Lerwick, 49 

Tiree and Leuchars (values estimated from Turnhouse prior to 1969), 

1957 to 2004 

Figure 47 Annual mean wind speed (knots) for Scottish regions, 1969 to 2004. 49 

Figure 48 Annual days of gale for three Scottish stations: Lerwick, Tiree and 50 

Leuchars (values estimated from Turnhouse prior to 1969), 1957 to 2004 

vi


Appendices 

Appendix 1 

Appendix 2 

Appendix 3 

Data availability scoping study............................................................................59 

A brief discussion of uncertainty in climate modelling.........................................87 

Glossary..............................................................................................................91 

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viii

SNIFFER Project CC03: Patterns of Climate Change across Scotland April 2006 

1. INTRODUCTION 

Over recent decades the scientific community has amassed a wealth of observational data. 

The last one hundred years have been a period of rapid climate change, partly in response to 

human influences. Social, economic, industrial, and land use developments all contribute to 

human impact on our climate, locally, nationally and globally. The changes already observed 

have had, and continue to have, impacts on many aspects of society, including health, 

agriculture, water resources and energy demand. In order to make appropriate plans for the 

future it is vital to investigate observed changes in climate. In doing so, models of past and 

present climate can be validated and scenarios of future climate put into the context of any 

change already recorded. 

Of the national climate trends studies conducted to date most have made use of data from a 

small number of stations with long historical records (e.g. Begert et al., 2005). Some authors 

have combined data from several stations to create a single series for a country (e.g. Hanna 

et al., 2004, for Iceland). In a study of UK climate, Jones and Lister (2004) have shown that 

the Scottish mainland and Scottish Isles warmed by 0.69°C and 0.64°C respectively over the 

period 1861 to 2000. Over a similar period, it can be shown that precipitation patterns over 

Scotland have altered (Osborn et al., 2000): summers have become drier and winters wetter. 

There has also been an increased frequency of heavy rain events (Mayes, 1996; Smith, 

1995). However, annual average figures for Scotland can mask significant regional and 

seasonal variations. 

As the evidence of climate change has increased, so has our understanding of the Earth’s 

climate, and improvements have been made to the mathematical models used to simulate it. 

Using climate models it has now been determined that not all of the changes observed can 

be attributed to natural causes and that a man-made, or anthropogenic, component can be 

discerned (IPCC, 2001). It is now possible to detect the signals of such anthropogenic 

changes at not only a global scale but also regionally (Stott et al., 2003; Stott, 2003). 

In order to plan for adaptation to climate change there is a need to know the degree of 

change already experienced in specific locations throughout the seasons. It is also 

necessary to consider observed trends for that locality in the context of potential future trends 

suggested by the latest UK Climate Impacts Programme (UKCIP) climate change scenarios 

(Hulme et al., 2002). This is true for all sectors of society and business, whether for the 

management of land, water resources, nature conservation, or building and maintenance of 

infrastructures. There have been a number of publications that consider the changing climate 

of the UK or its regions (e.g. Kerr et al., 1999; Hulme et al., 2002; Jenkins et al., 2003; etc). 

Although some of these publications have focused upon Scotland, there is still the need for 

one publication to present a consistent analysis of available Scottish data and to place 

observed trends of change into the context of the latest climate model predictions. This study 

seeks to resolve this need. 

The aim of this study is to collate records of observed data in order to provide an up to date 

assessment of how the climate of Scotland has changed, not just giving a nationally 

averaged result but showing the regional patterns of change. This study provides a 

benchmark against which future change can be measured and its implications assessed. The 

analysis of trends shows how far Scotland’s climate has altered and provides the context 

against which climate change impacts may be examined. 

The analysis presented here provides an assessment of climate data for the whole of 

Scotland that has been collated to show seasonal and regional trends for a range of 

variables. It places these trends in the context of climate model predictions of Scotland’s 

1


future climate (taken from the UKCIP02 scenarios, Hulme et al., 2002), and briefly discusses 

uncertainties associated with these predictions. 

This technical report is structured as follows. Section 2 focuses upon observed changes in 

Scottish climate. It begins with a description of the framework for the analysis and then, in 

section 2.1, discusses the datasets used and the analysis methods employed. Trends in 

temperature, including derived quantities such as growing season length and heat wave 

duration, are presented in section 2.2. Analysis of precipitation variables, again including 

some derived variables, is shown in section 2.3, which is followed by trends in snow and frost 

in section 2.4. Changes in sunshine and cloud are given in sections 2.5 and 2.6. The 

analysis of observed change concludes with a presentation of trends in mean sea level 

pressure (section 2.7) and wind (section 2.8). In section 3 predicting the future climate of 

Scotland is discussed, and the trends identified in the analysis of historical data are placed in 

the context of the UK Climate Impacts Programme 2002 scenarios (Hulme et al., 2002). 

Concluding remarks are given in section 4. A handbook is also available which summarises 

the findings described in this technical report. 

2


2. OBSERVED TRENDS IN SCOTTISH CLIMATE 

There are many sources of observed climate data for Scotland. Records for particular 

variables at individual locations are available from a wide range of sources for differing 

periods of time (see Appendix 1). A number of these datasets have been collated into 

gridded datasets using spatial interpolation techniques. Datasets are often available free of 

charge, often under a licence agreement although access to some requires a fee. This study, 

for ease of accessibility for the reader, relies upon datasets that are readily available to the 

general public, although these have been supplemented by datasets available to the authors. 

The use of accessible data ensures that the analysis may be readily updated in the future. 

Initially, a scoping study sought to identify relevant climate datasets and to assess their 

availability, plus suitability, for the proposed analysis. In addition, a survey was undertaken to 

assess what derived variables (in addition to standard temperature and precipitation 

datasets) would be of most interest to a range of stakeholders across Scotland. The scoping 

study report, including the dataset listings, is presented in Appendix 1. The majority of 

gridded datasets identified are available from 1961 until the end of 2004, although there are 

exceptions to this. In particular, much longer records exist for temperature, rainfall and 

sunshine. To assess whether trends can be detected in observed records of Scottish climate, 

it is highly desirable to use as long a data record as possible. On the other hand, using a 

consistent period of history for all variables allows a comprehensive picture of change, and 

any inter-dependencies, to be identified most clearly. For this reason, all data were analysed 

for the period 1961 to 2004 (or less where records are not available throughout the full 

period). However, where longer records exist these were also analysed and presented 

alongside the 1961 to 2004 analysis. Where gridded datasets do not exist or are difficult to 

interpret due to inhomogenities in the data (e.g. a change in instrumentation or observing 

site) individual site records were used. 

The Met Office has a historical database containing observations of weather elements. 

These observations come from an irregularly spaced and gradually evolving network of 

meteorological stations across the United Kingdom. From this dataset a consistent series of 

climatic statistics have been produced which enables comparisons to be made across space 

and time. In order to do this, methods were developed to create gridded datasets from the 

station data. 

The analysis process used geographical information system (GIS) capabilities to combine 

multiple regression, based on factors such as altitude, terrain shape and nearby sea or urban 

areas, with inverse-distance-weighted interpolation of the regression residuals. A verification 

of the gridded results compared with observed values was also undertaken. The full method 

is described in Perry and Hollis (2005a; 2005b). Although the gridded datasets have been 

verified using independent observations, they are the result of interpolation techniques and 

therefore the maps of trends derived from this data should be taken only as indicative of local 

patterns of change as the techniques employed to construct the datasets from point location 

data may influence the finer detail of the patterns. 

The Met Office dataset is notable for the range of climate elements included: gridded data 

sets at 5km by 5km resolution over the UK have been produced for 36 monthly or annual 

climate variables, for the period 1961-2000. The start date of 1961 was chosen because 

there is a significant increase in the availability of digitised data from this point. A number of 

these variables are routinely updated with the latest month while several other variables have 

been updated to 2004 for this study. 

The density of the station network varies between elements. An example of the distribution of 

stations in the observing network is shown in Figure 1 below. The left hand panel shows the 

3


location of sites which recorded temperature and/or precipitation in January 2001. The 

location of sites that recorded pressure and/or sunshine is given in the right-hand panel. This 

is a snapshot of the status of the network in January 2001 but it must be noted that the 

number of stations within the network changes over time. For example, the number of 

sunshine stations reached a peak of one hundred in the early 1970s but has since been 

reduced, such that there were only forty eight in Scotland in January 2001 (as seen in Figure 

1). The network of precipitation recording stations is of the highest density average while the 

distribution of pressure and sunshine observing sites is of the lowest density for the variables 

included in the gridded dataset. Networks are comparatively sparse in certain areas, 

especially those that are sparsely populated, e.g. the Scottish Highlands. 

Figure 1 - Location of observing sites (January 2001) for data used in the construction 

on the Met Office gridded datasets. Precipitation and temperature sites are shown in the 

left-hand panel. Sites recording sunshine and/or pressure are shown in the right-hand panel. 

All available monthly meteorological data are used in the construction of the dataset in order 

to make maximum use of the information available and ensure that the most accurate 

possible representation of the climate can be made for each month. Consequently, the 

network of stations used changes slightly each month, and the methods used are designed 

specifically to minimise the impact of these changes on the consistency of the datasets 

through time. Table 1 shows, by variable, the average number of stations included in a 

month of the dataset. The average number of stations for the variables available before 1961 

is also given, clearly showing the increase in available digitised data since this time. 

4


Table 1 - Average number of stations included per month in the gridded dataset. 

Climate variable Pre-1961 1961 onwards 

Precipitation 102 740 

Days of rain >= 10 mm n/a 693 

Rainfall intensity / greatest 5-day rainfall n/a 458 

Air temperature 76 158 

Annual consecutive dry days n/a 145 

Annual extreme temperature range n/a 141 

Heating and growing degree days n/a 126 

Days of snow cover n/a 106 

Sunshine 59 75 

Heat and cold wave duration n/a 52 

Mean sea level pressure / cloud n/a 19 

The values of climate variables at locations between observing stations can be estimated to 

a good degree of accuracy, producing detailed and representative maps of the Scottish 

climate. Spatial and temporal variability and trends in climate can be investigated using the 

results of the gridding, which provides a consistent set of data. It must be noted however that 

accuracy varies and is dependent on the nature of the variable plus the density and 

representivity of the station network. Errors are highest in areas of sparse station coverage, 

particularly the highlands of Scotland, which are also areas of complex mountainous terrain. 

Localised effects on climate such as frost hollows, and effects caused by soil type and 

forests, have not been taken into account. Additionally the methods used to generate the 

dataset have not been optimised for complex variables such as wind. The difficulties in 

identifying trends in a number of variables presented in this report are discussed in each 

relevant section. 

It is recognised that globally averaged temperatures have increased over the last century but 

that the increase has not been a linear one (IPCC, 2001). During the first half of the twentieth 

century observed global mean temperatures increased. This was followed by a decreasing 

trend throughout the fifties and sixties before temperatures once again began to rise, 

although at a faster rate than seen previously. Also, while nine of the ten warmest years 

observed (based on global average figures) have been within the last decade the warmest 

individual year globally occurred in 1998. Subsequent years have failed to exceed this record 

temperature although 2005 recorded the second warmest annual mean global temperature 

and the warmest northern hemisphere annual mean on record. The record temperatures of 

1998 are likely to be due, in part, to a prolonged El Niño event. El Niño Southern Oscillation 

(ENSO) is one of a number of cycles, including sun spot activity, which combine to produce 

the variability that naturally occurs on a number of different time scales within our weather 

and climate. Natural variability also results in the record breaking annual mean temperatures 

occurring regionally in different years, for example, 2003 was the warmest year that has 

been observed in Scotland. 

In order to minimise the signal of this natural variability, climatologies are constructed from 

long-term average of weather, typically thirty years. The World Meteorological Organisation 

(WMO) publishes updated climatologies every decade. Currently the most widely used of 

these WMO climatological periods is 1961 to 1990. This is the period used to define a 

‘baseline’ or ‘control’ climate for many climate modelling studies, including those in the 

Intergovernmental Panel on Climate Change’s Third Assessment Report (IPCC, 2001) and 

the United Kingdom Climate Impacts Programme Climate Change Scenarios for the United 

Kingdom (UKCIP02, Hulme et al., 2002). The 1971 to 2000 climatology is also available. 

Where it aids understanding a climatology is included in this text. More images are also 

available from the Met Office website (www.metoffice.gov.uk). Further details of the mapped 

climatological variables available are given in the scoping study report (see Appendix 1). 

5


2.1. Data analysis 

The analysis is presented in a three-tier manner: 

• Firstly, linear trends were calculated for each variable for Scotland as a whole and for 

three regions (e.g. Figure 2). This was done for annual and seasonal mean periods. The 

seasons used in this work are as follows: December, January and February (DJF, winter); 

March, April and May (MAM, spring); June, July and August (JJA, summer); and September, 

October, and November (SON, autumn). The three regions are the same as those typically 

used by the Met Office to generate descriptions of regional weather and climate. Each region 

encompasses an area of similar climatic characteristics. For the purposes of this report they 

have been termed North, West and East Scotland 1 . A linear regression equation was 

calculated for each dataset and then the trend was calculated from the gradient parameter 

(i.e. the rate of change) multiplied by the length of the data period to provide a clear change 

value since the start of the period. The Mann-Kendall test was then used to show whether 

significant changes have occurred. Where these trends are statistically significant they are 

shown as either bold (significant at the 1% level) or italic (significant at the 5% level) type 

(e.g. Table 2). Significance at the 1% level is equivalent to saying that there is a confidence 

level of 99% that the identified trend cannot be explained by natural variability. Equally, 

significance at the 5% level equates to 95% confidence that the trend is beyond that which 

could be explained by natural variability. Where text is in neither bold nor italic font then there 

is less than 95% confidence that a trend exists. It is possible that trends may be identified 

with less stringent significance/confidence criteria, however these have not been explored 

here. 

• Secondly, graphs of the time-series for each variable were produced for each of the three 

regions of Scotland. These demonstrate the inter-annual variability that exists in each 

variable and include a smoothed version of the data as an indication of the longer-term 

trends and variations (see Figure 3 for an example). 

• Finally, where appropriate, a map of observed trends was produced showing the spatial 

variation not apparent from the national average figures often presented elsewhere. (See 

Figure 4 as an example). 

The time series data were smoothed by applying a triangular-shaped kernel filter, with 14 

terms either side of each target point 2 . This non-parametric filter, effectively a running mean 

with weighting, enables the long-term fluctuations in the climate to be clearly seen without 

assuming that the trend follows a stated model. It was applied to the regional data in order 

that changes in different parts of Scotland could be compared. 

The data were analysed for trends using linear regression, and the significance of trends was 

tested using the non-parametric Mann-Kendall tau test 3 (Sneyers, 1990). Care needs to be 

taken when interpreting results from linear trends as the assumption of a linear trend is not 

always valid. However, the trends do often approximate to linear, and the combination of 

1 The convention is taken that only when discussing one of the three regions, as defined for this study, is a capital 

letter used, i.e. North Scotland. The capital letter is not used when describing areas of the mapped changes, i.e. 

northern Scotland. 

2 The kernel filter is a non-parametric smoothing technique, where, in this case, each point is replaced by a 

weighted average of the target point and 14 points on either side, with the weights being determined by a 

triangular-shaped kernel centred on the target point. 

3 The Mann-Kendall test is a rank-based non-parametric test. For each value in the series, the number of 

preceding values which exceed it is calculated, and this is used to gain evidence for the existence of a trend in the 

data series. 

6


linear trends with the Mann-Kendall significance test has been widely used in the analysis of 

climate trends (e.g. Domroes and El-Tantawi, 2005; Shen et al., 2005). 

Figure 2 - Map of Scotland showing boundaries of the three regions as defined in this 

study (North, West and East Scotland). 

As with the regional and national series, linear trends were also calculated for series within 

each individual 5km x 5km grid cell of the gridded datasets. This enabled the mapping of 

changes in climate variables over the period of study, so that the spatial differentiation of 

changes can be clearly seen. 

The analysis methods described here are consistent with the methods being used by the Met 

Office in an on-going analysis of trends in UK climate. 

2.2. Temperature 

Records of temperature are probably the most frequently analysed of all meteorological 

records. Some of the longest records of weather variables are for temperature. The Met 

Office gridded dataset covers the period 1914 to 2004. Seasonal and annual changes in 

mean temperature (°C) for three regions of Scotland are presented below (Table 2). It can be 

seen that the increase in temperature observed since 1961 is statistically significant in each 

region and every season, with the exception of winter in North Scotland. The trends since 

1914 have not been as large, although annual average temperature for the whole of Scotland 

7


has increased significantly. At a regional level there have been significant temperature rises 

since 1914, particularly in East and West Scotland where temperatures have risen from an 

annual average of approximately 6.7°C (East Scotland) and 7.8°C (West Scotland) to 7.5°C 

and 8.3°C respectively. The apparent inconsistency between these two sets of figures, with 

the fact that more of the regions and seasons show significant trends during the later 

(shorter) period, suggests a more rapid rise in temperatures over this later part of the 

twentieth century. This can also be seen in Figure 3, which presents the ninety-year timeseries 

of annual mean temperatures for the regions (1914 to 2004). 

Table 2 - Mean Temperature changes (°C), 1961 to 2004 and 1914 to 2004. Statistically 

significant trends are shown in bold (significant at the 1% level) or italic (significant at the 5% 

level) type. 

1961-2004 1914-2004 

North East West 


Scotland Scotland Scotland Scotland Scotland Scotland Scotland Scotland 

Spring 1.03 1.23 1.20 1.14 0.59 0.83 0.66 0.69 

Summer 1.06 1.12 1.08 1.08 0.50 0.59 0.43 0.51 

Autumn 0.64 0.68 0.66 0.66 0.46 0.85 0.68 0.64 

Winter 1.03 1.39 1.31 1.22 0.02 0.45 0.33 0.24 

Annual 0.92 1.08 1.04 1.00 0.37 0.66 0.51 0.50 

Figure 3 - Annual mean temperature (°C) for Scottish regions, 1914 to 2004, with 

smoothed curve. The vertical dashed line marks the position of 1961. 

Annual Mean temperature for the three Scottish districts, with 30-year smooth filter, 1914-2004 

9.0 

8.5 

Mean temperature (deg C) 

8.0 

7.5 

7.0 

6.5 

6.0 

5.5 

1914 

1917 

1920 

1923 

1926 

1929 

1932 

1935 

1938 

1941 

1944 

1947 

1950 

1953 

1956 

1959 

1962 

1965 

1968 

1971 

1974 

1977 

1980 

1983 

1986 

1989 

1992 

1995 

1998 

2001 

2004 

N Scotland 

E Scotland 

W Scotland 

The pattern of Scottish regional temperature change (Figure 3), where the weighted running 

mean is shown by the smoothed curve, is very similar to that seen in the global mean 

temperature time-series (not shown). Here there is an increase throughout the first half of the 

twentieth century, then a decrease throughout the fifties and sixties before rising once again 

toward the end of the century. It is also clear that average annual temperature in each region 

is now higher than at any other time in this record, i.e. since 1914. The inter-annual, or yearby-year, 

variation in temperatures is also apparent in Figure 3. It is interesting to note that 

whilst the West Scotland region is slightly milder than the other two, that all three regions see 

very similar inter-annual variation across the period, i.e. when one region experiences a 

warm or cold year so do the other two. The mapped trends in seasonal mean temperature for 

the period 1961 to 2004 are presented in Figure 4. It can be seen that average seasonal 

temperatures have increased everywhere in Scotland during this period, although the 

8


increases are smallest during autumn and largest in southern and eastern Scotland in winter. 

Results from this study concur with the results of Jones and Lister (2004), which 

demonstrated that there has been a significant increase in annual mean temperature over 

the whole of the UK during the last century. 

Figure 4 - Gridded change for mean temperature (°C) from 1961 to 2004, based on a 

linear trend: a) spring (MAM), b) summer (JJA), c) autumn (SON) and d) winter (DJF). 

9


The 24-hour or daily maximum and minimum temperature datasets also exhibit a warming 

trend. The changes for 24-hour maximum temperature are tabulated for each region and 

season below (Table 3). As previously, trends for 1961 to 2004 are shown alongside those 

calculated from 1914 to 2004. In the 1961 to 2004 period each region shows a statistically 

significant increase in maximum temperature. Moreover, increases in daily maximum 

temperature have been consistently greater than those in the mean temperature. However, 

the same is not true of the full ninety-year record. Significance is found in the annual mean 

figures but not consistently in the seasonal means (only spring in North and East Scotland, 

autumn in East Scotland and winter in West Scotland). In addition, since 1914 it is only in 

North Scotland that daily maximum temperatures have increased at a faster rate than daily 

mean temperatures. 

Table 3 - 24-hour maximum temperature changes (°C), for 1961 to 2004 and 1914 to 

2004. Statistically significant trends are shown in bold (significant at the 1% level) or italic 

(significant at the 5% level) type. 

1961-2004 1914-2004 

North 

Scotland 

East 


West 

Scotland Scotland 

North 


East 


West 


Spring 1.16 1.41 1.35 1.29 0.70 0.71 0.48 0.64 

Summer 1.11 1.14 1.12 1.12 0.58 0.37 0.20 0.40 

Autumn 0.85 0.83 0.83 0.84 0.58 0.66 0.46 0.57 

Winter 1.16 1.51 1.47 1.36 0.41 0.58 0.42 0.47 

Annual 1.14 1.29 1.25 1.21 0.59 0.60 0.41 0.54 

Changes in 24-hour minimum (effectively night-time) temperatures present a more complex 

pattern of change (Table 4). As with maximum temperatures all increases since 1961 are 

significant, although some increases are at a slower rate than for mean temperatures. Since 

1914 there has been a significant upward trend (at the one percent level) in night-time 

minimum temperatures in the East and West of Scotland in all seasons except for winter. 

These trends are for warming at a rate faster than the mean temperature. In contrast to this, 

the average winter minimum temperatures have decreased in North Scotland since 1914, 

although none of the winter trends over this period are statistically significant. 

Table 4 - 24-hour minimum temperature changes (°C), for 1961 to 2004 and 1914 to 



1961-2004 1914-2004 

North 


East 


West 


North 


East 


West 


Spring 0.89 1.08 1.07 1.00 0.46 1.00 0.94 0.76 

Summer 1.07 1.18 1.11 1.12 0.30 0.80 0.65 0.55 

Autumn 0.55 0.64 0.56 0.58 0.39 1.12 0.99 0.79 

Winter 0.96 1.32 1.22 1.15 -0.37 0.35 0.22 0.02 

Annual 0.94 1.13 1.06 1.03 0.22 0.84 0.73 0.56 

Comparing the data in Tables 3 and 4 it is clear that since 1961 daytime maximum 

temperatures have increased at a faster rate than night-time minimum temperatures. This is 

contrary to the global trend identified in the IPCC Third Assessment Report (IPCC, 2001). 

The IPCC report, based upon analysis of data from 1950 to 1993, showed that, on average, 

night-time daily minimum temperatures increased at approximately twice the rate of daytime 

daily maximum temperatures. It is interesting to note that extending the period of analysis 

back to 1914 shows that the warming trends in maximum and minimum temperature in the 

10


East and West Scotland regions are more like the global average reported by the IPCC 

(2001). 

As with mean temperature the pattern of warming, cooling and then warming again can be 

seen in the regional time-series of both the annual mean 24-hour minimum and maximum 

temperature time-series (Figures 5 and 6). The rate of change in maximum temperature is 

similar in each region but minimum temperatures in North Scotland are increasing at a 

slower rate than in the other two regions. East Scotland has moved from an annual climate 

with lower night-time minimum temperatures than North Scotland to one which experiences 

very similar annual means. 

Figure 5 - Annual average 24-hour maximum temperature (°C) for Scottish regions, 

1914 to 2004, with smoothed curve. The vertical dashed line marks the position of 

1961. 

12.5 

12.0 

Maximum temperature (deg C) 

11.5 

11.0 

10.5 

10.0 

9.5 

9.0 

8.5 

1914 

1918 

1922 

1926 

1930 

1934 

1938 

1942 

1946 

1950 

1954 

1958 

1962 

1966 

1970 

1974 

1978 

1982 

1986 

1990 

1994 

1998 

2002 

11 

Scotland N 

Scotland E 

Scotland W 

Figure 6 - Annual average 24-hour minimum temperature (°C) for Scottish regions, 

1914 to 2004, with smoothed curve. The vertical dashed line marks the position of 

1961. 

Minimum temperature (deg C) 

6.0 

5.5 

5.0 

4.5 

4.0 

3.5 

3.0 

2.5 

2.0 

1914 

1918 

1922 

1926 

1930 

1934 

1938 

1942 

1946 

1950 

1954 

1958 

1962 

1966 

1970 

1974 

1978 

1982 

1986 

1990 

1994 

1998 

2002 



Scotland W


Maps of trends in the gridded data (1961 to 2004) are shown for the winter (December- 

February) and summer (June-August) seasons for 24-hour maximum temperature and 24- 

hour minimum temperature in Figures 7 and 8. Typically the greatest rises in temperature 

have occurred in the winter rather than summer season. Winter patterns of change for both 

are similar to that of mean temperature (Figure 4). In particular, the most rapid warming 

trends are in southern Scotland in the winter season. Parts of northern Scotland have seen 

relatively little increase in minimum temperatures over the 1961 to 2004 period. Minimum 

temperatures have increased during summer months at a faster rate in northern, eastern and 

southern Scotland than in central areas or the Highlands. In contrast, the rise in summer 

daily maximum temperatures has been relatively uniform across the country except for the 

Shetland Islands, where a cooling has been recorded. 

Figure 7 - Gridded change for 24-hour maximum temperature (°C), based on a linear 

trend from 1961 to 2004: a) summer quarter, b) winter quarter 

12


Figure 8 - Gridded change for 24-hour minimum temperature (°C), based on a linear 

trend from 1961 to 2004: a) summer quarter, b) winter quarter. 

With maximum temperatures increasing at a faster rate than minimum temperatures since 

1961, it is likely that the daily, or diurnal, temperature range (DTR) will also have increased. 

This is indeed the case as can be seen the regionally averaged changes in DTR for 1961 to 

2004 (Table 5). With the exception of the summer season in East Scotland the diurnal 

temperature range has increased in all regions and seasons. Summer increases are modest 

for all regions and not statistically significant. However, North Scotland has seen significant 

increases in DTR during the autumn season and significant increases have occurred in the 

winter season across the country as a whole. The time-series of diurnal temperature range 

for the regions since 1961 clearly shows that the three regions are well correlated, indicating 

that patterns of change are likely to be large scale (Figure 9). 

Table 5 - Mean diurnal temperature range changes (°C), 1961 to 2004. Statistically 


level) type. 

North 


East 


West 


Spring 0.30 0.24 0.27 0.27 

Summer 0.09 -0.06 0.01 0.02 

Autumn 0.46 0.24 0.32 0.35 

Winter 0.45 0.30 0.37 0.38 

Annual 0.33 0.19 0.23 0.26 

13


Figure 9 - Annual mean diurnal temperature range (°C) for Scottish regions, 1961 to 

2004, with smoothed curve. 

8.0 

Diurnal temperature range (deg C) 

7.5 

7.0 

6.5 

6.0 

5.5 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




In addition to temperature records, a number of temperature related variables can be derived 

for each year. These variables have particular significance for several sectors and can be 

better related to direct climate impacts. The derived temperature variables analysed in this 

report are: 

• Heating degree-days (HDD) 4 . This is an indicator of household consumption of heat 

energy. The base temperature for calculation of a heating degree day is 15.5°C, such that if 

the mean temperature were below 15.5°C then the value of the HDD for that individual day 

would be 15.5°C minus the mean temperature. For example, if a day has a mean 

temperature of 13.5°C this is equivalent to 2.0 heating degree days. This figure represents 

the energy input required to keep a building at a constant temperature. Typical figures at the 

start of the 1961 to 2004 period were approximately 3200 HDD per annum for North and 

East Scotland, and 2900 HDD per annum for West Scotland. 

• Growing degree-days (GDD) 5 . This is an accumulated sum for mean temperatures above 

a threshold assumed to represent the temperature above which plants are photosynthetically 

active. In this report, a threshold of 5°C is used and the calculation is very similar to that of 

HDD. For example, if mean temperature for a day is 7.5°C this equates to 2.5 growing 

degree days. Typical values in the early 1960’s were approximately 950 GDD per annum in 

North Scotland, 1000 GDD per annum in East Scotland and 1150 GDD per annum in West 

Scotland. 

• Growing season start (GSS). This is the start date for the growing season (calculated 

as Julian days), where the growing season is assumed to start on the 5 th consecutive day 

with a mean temperature of 5°C or greater. During the 1960s the typical start date for the 

growing season was 12 th April in East Scotland, 10 th April in North Scotland and 29 th March in 

West Scotland 

4 Heating Degree Days = ∑ (15.5 – daily T_mean) for T_mean < 15.5 °C 

5 Growing Degree Days = ∑ (daily T_mean – 5) for T_mean > 5 °C. 

14


• Growing season end (GSE). This is the end date for the growing season (calculated in 

Julian days), where the growing season is assumed to end on the 5 th consecutive day with a 

mean temperature of 5°C or less. During the 1960s the typical end date for the growing 

season was 10 th November in East Scotland, 12 th November in the North and 20 th November 

in the West. 

• Growing season length (GSL) 6 . This is the number of days between the start and end of 

the growing season i.e. GSE-GSS. In the early 1960s typical values were a growing season 

of approximately 213 days in East Scotland, 217 days in North Scotland and 237 days in the 

West. 

• Extreme Temperature Range (ETR) is defined as the range between the highest 

maximum and lowest minimum temperature within each year. 

• Cold wave duration 7 is calculated for a half-year period, either winter or summer. In this 

study, it is defined to be the total length of periods of at least 6 days, during the summer halfyear 

(April to September) or winter half-year (October to March), when the minimum 

temperature is at least 3°C less than the 1961-1990 average for that day. 

• Heat wave duration 8 . This is also is calculated for half-year periods. It is defined as the 

total length of periods of at least 6 days, during either the summer half-year or winter halfyear, 

when the maximum temperature exceeds the 1961-1990 average for that day by at 

least 3°C. 

Changes in some of these derived quantities since 1961 are presented in Table 6. It can be 

seen that in all areas of Scotland the number of heating degree days have decreased 

significantly. There has also been a significant increase in the number of growing degree 

days, and an associated increase in the length of the growing season. These changes are 

likely to be primarily due to the significant increases in both minimum and mean 

temperatures in the spring although increases in autumn temperatures will contribute. 

Table 6 - Changes in annual temperature indices: a) heating degree days, 1961 to 2003 

(%), b) growing degree days, 1961 to 2003 (%), c) growing season length, 1961 to 2004 

(days), d) growing season start, 1961 to 2004 (days), e) growing season end, 1961 to 

2004 (days) and f) extreme temperature range, 1961 to 2003 (°C). Statistically significant 

trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) 

type. 

North 


East 


West 


Heating Degree Days (%) -9.2 -10.7 -11.3 -10.2 

Growing Degree Days (%) 23.7 22.5 21.1 22.5 

Growing Season Length (days) 31.1 32.5 36.7 33.2 

Growing Season Start (days 9 ) -19.6 -20.6 -22.4 -20.7 

Growing Season End (days) 11.5 12.0 14.4 12.5 

Extreme Temperature Range (°C) 0.0 -3.4 -2.2 -1.8 

6 Growing Season Length = period (days) bounded by daily T_mean > 5 °C and < 5 °C for > 5 days 

7 Cold Wave Duration = ∑ days with 1961-1990 daily normal - daily T_min > 3 °C for ≥ 6 consecutive days 

8 Heat Wave Duration = ∑ days with daily T_max – 1961-1990 daily normal > 3 °C for ≥ 6 consecutive days 

9 A negative number of days indicates a date earlier in the year, i.e. growing season starting earlier in the year. 

15


The contribution of the higher temperatures is confirmed by the trends in growing season 

start and end dates (Table 6). As previously noted, during the 1960s the typical start date for 

the growing season was 12 th April in East Scotland, 10 th April in North Scotland and 29 th 

March in West Scotland. At the same time, the typical end date for the growing season was 

10 th November in East Scotland, 12 th November in the North and 20 th November in the West. 

The growing season is now starting almost three weeks earlier in North and East Scotland, 

and more than three weeks earlier in the West. Whilst the growing season is also ending 

later, it is by less than two weeks in the North and East and just over two weeks in the West. 

The changes to the start and end of the growing season are statistically significant in all 

regions. 

The changes indicated by the extreme temperature range (ETR) are not straightforward to 

interpret (Table 6). These trends are not significant and, in fact, ETR appears to be reducing. 

This would suggest that the increase in the lowest minimum temperature each year is 

occurring at a faster rate than the increase in the highest maximum temperature. However, it 

should also be noted that the result is not significant so it may simply be “noise” within the 

data resulting from natural variability in extremes. 

Figures 10 to 15 show time-series for these derived temperature variables since 1961. It is 

clear that in each case the regions show similar inter-annual variability indicating that the 

causal factors are likely to be large scale. However, the maps of trends presented in Figure 

16 to 19 show that there is considerable spatial variation in the trends, often related largely to 

topography. 

Figure 10 - Annual heating degree days for Scottish regions, 1961 to 2003, with 

smoothed curve 

3500 

3400 

Heating degree days 

3300 

3200 

3100 

3000 

2900 

2800 

2700 

2600 

2500 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




16


Figure 11 - Annual growing degree days for Scottish regions, 1961 to 2003, with 


1500 

1400 

Growing degree days 

1300 

1200 

1100 

1000 

900 

800 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




Figure 12 - Annual growing season length (days) for Scottish regions, 1961 to 2004, 

with smoothed curve 

Growing season length (days) 

310 

290 

270 

250 

230 

210 

190 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




17


Figure 13 - Growing season start dates (days from 1 st January) for Scottish region 

from 1961 to 2004, with smoothed curve. 

Start of the growing season (days from 1st January) 

130 

120 

110 

100 

90 

80 

70 

60 

50 

40 

30 

20 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 

East Scotland 

North Scotland 

West Scotland 

Figure 14 - Growing season end date (days from 1 st January) for Scottish regions from 

1961 to 2004 with smoothed curve. 

End of the growing season (days from 1st January) 

360 

350 

340 

330 

320 

310 

300 

290 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




18


Figure 15 - Annual extreme temperature range (°C) for Scottish regions, 1961 to 2003, 


Extreme temperature range (deg C) 

45 

43 

41 

39 

37 

35 

33 

31 

29 

27 

25 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




The patterns of change in heating degree days (HDD, Figure 16) mimic the temperature 

grids to some extent, with the southerly, coastal and lower lying areas exhibiting the greatest 

change. Areas of large decrease are also evident in the Shetlands and the Outer Hebrides. 

Growing degree day patterns of change (GDD, Figure 16) appear to be more uniform, 

although localised areas of large increase are evident within the highland areas of the north 

of Scotland, the Outer Hebrides, Orkney and Shetland Islands. 

Figure 16 - Gridded change for a) growing degree days (percentage) and b) heating 

degree days (percentage) based on a linear trend from 1961 to 2003 

19


The Extreme Temperature Range (ETR, Figure 17), on the other hand, exhibits a complex 

pattern with strong increases exhibited for some of the Western Isles and the Orkneys as 

well as the more mountainous areas surrounding Fort William and Inverness and the Great 

Glen joining these two areas. The Outer Hebrides and Shetland Islands display the opposite 

trend, as does much of the rest of the country. It must be remembered however that regional 

trends in ETR were small and not significant. The percentage changes shown here are also 

modest, typically less than five percent. It is not clear what confidence, if any, can be placed 

in the significance of this pattern of change. 

Figure 17 - Gridded change for extreme temperature range (°C) based on a linear trend 

from 1961 to 2003. 

In this study, the spatial analysis of growing season length, start and end dates is slightly 

different to that of the other derived variables, in that it is based directly upon the baseline 

observed climate of the UK dataset provided by the Met Office for UKCIP with the UKCIP02 

scenarios. The dataset, based upon observed rather model data, provides monthly mean 

temperatures rather than the daily values required to calculate growing season, so a sine 

curve interpolation has been used to estimate daily values based on the method of Brooks 

(1943). These daily data were then used within the calculations for growing season length, 

start and end dates. Additionally, the standard UKCIP02 observed climate dataset is for 

1961-2000, but for this application it has been updated to 2004. 

The presentation style of the three growing season maps (Figures 18 and 19) is intentionally 

slightly different to the others in this technical report. This has been done in order to visually 

separate them from the other figures, as they have been derived using an estimation 

technique, thereby introducing additional uncertainty. A gridded dataset of growing season 

start and end could be constructed from existing data, however this is not a trivial task and 

no such dataset exists at this time, hence the use of the method employed here. 

20


It has already been shown that the increasing growing season length is occurring as a result 

of both an earlier start and a later end to the season. This is seen in the mapped patterns of 

change presented in Figures 18 and 19. The greatest increases in growing season length are 

in coastal areas and the Shetland Islands where the season has extended by two months, or 

more. The regional averages discussed previously mask the fact that the length of the 

growing season has changed very little since 1961 in many areas, particularly in more 

mountainous areas. Further investigation would be required to investigate whether there has 

been a change in growing season at increasing altitude in these areas. The pattern of 

change for growing season start and end is similar to that for growing season length. Again, 

coastal areas show a greater tendency towards an earlier start and later end to the growing 

season than central Scotland. The longer growing season, and in particular the earlier start, 

has already been observed through a change in flowering dates of plants particularly those 

flowering in early spring (Roberts et al., 2004). 

Figure 18 - Gridded change for growing season length (days) based on a linear trend 

from 1961 to 2004 calculated from the extended UKCIP02 dataset. 

21


Figure 19 - Gridded change for the (a) start and (b) end of the growing season (days), 

based on a linear trend from 1961 to 2004. Negative values indicate an earlier start/end to 

the season. 

Changes in heat wave and cold wave duration are shown (in number of days) in Table 7. The 

only trends identified that are statistically significant are the decreases in cold wave duration 

during the winter half year (October to March) in East and West Scotland. Although an 

increase in heat wave duration is seen in all regions throughout the year the change is not 

significant and therefore it may be a result of natural variability, but is likely to result from the 

increase in mean temperature. 

Table 7 - Change in half-year heat wave 10 and cold wave duration 11 (days), 1961 to 



North 


East 


West 


CWDs 1.5 1.2 2.4 1.7 

CWDw -5.8 -8.4 -8.9 -7.5 

HWDs 6.3 6.3 4.3 5.7 

HWDw 6.0 6.6 7.1 6.5 

Time-series of winter half-year cold wave duration and summer half-year heat wave duration 

are shown in Figures 20 and 21. As with many of the other variables derived from 

temperature records it is clear that inter-annual variability is very similar in each of the 

10 Heat Wave Duration = ∑ days with daily T_max – 1961-1990 daily normal > 3 °C for ≥ 6 consecutive days. 

11 Cold Wave Duration = ∑ days with 1961-1990 daily normal - daily T_min > 3 °C for ≥ 6 consecutive days. 

22


regions. The patterns of change are shown in Figure 22. Winter cold wave duration has 

decreased most in southern Scotland and the Shetlands, a pattern that is well correlated with 

the pattern of winter temperature change. The duration of summer heat waves has increased 

most in inland and north eastern areas. 

Figure 20 - Winter half-year cold wave duration (days) for Scottish regions, 1961/62 to 

2003/04, with smoothed curve 

Winter cold wave duration (days) 

28 

26 

24 

22 

20 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 

23 




Figure 21 - Summer half-year heat wave duration (days) for Scottish regions, 1961 to 

2003, with smoothed curve 

Summer heat wave duration (days) 

35 

30 

25 

20 

15 

10 

5 

0 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 



W Scotland


Figure 22 - Gridded change for a) winter half-year cold-wave duration (days) and b) 

summer half-year heat-wave duration (days), based on a linear trend from 1961 to 

2003. 

2.3. Rainfall 

As with the temperature records presented in section 2.2 there is a long record of rainfall 

observations for Scotland. Where longer-term data records are available, the changes are 

presented alongside those for the 1961 to 2004 period. This is the case in Table 8. Here 

trends in total precipitation amount (i.e. rain and snow) over each period are expressed as a 

percentage change since the start of each period. What is most striking is the statistically 

significant increase in winter precipitation over the 1961 to 2004 period. In each region, and 

nationally, the winter change is statistically significant at the 1% level, based on the Mann 

Kendall test. In this analysis, over this specific period, an increase of almost seventy percent 

in winter precipitation since 1961 has been identified in North Scotland. This is equivalent to 

an average increase of approximately three millimetres a day throughout the winter season 

(December to February). Annually averaged precipitation has also increased significantly 

over the same period. As a whole, Scotland has become twenty percent wetter during the 

period 1961 to 2004, equivalent to an average increase of approximately 240 millimetres of 

rainfall a year. Conversely, there has been little or no change in regionally averaged summer 

rainfall totals, although a slight decrease (seven percent) can be identified in the northern 

region. Over the same period summer rainfall has increased by a similar amount in West 

Scotland. Changes in summer rainfall are not however significant for the 1961 to 2004 

period. 

24


Table 8 - Changes in total precipitation amount (percentage), 1961 to 2004 and 1914 to 



1961-2004 1914-2004 




Spring 16.2 9.4 17.3 14.8 13.9 6.1 22.0 14.3 

Summer -7.0 0.2 7.3 -0.6 -12.7 -18.9 -7.5 -12.7 

Autumn 5.3 22.2 5.9 9.1 13.6 0.7 15.6 11.1 

Winter 68.9 36.5 61.3 58.3 20.9 -0.8 9.0 11.6 

Annual 21.0 18.4 23.3 21.1 9.6 -3.5 9.5 6.2 

When the time-series is extended to consider the full period 1914 to 2004 the trend is less 

well established. Over the longer period the statistically significant trends identified are 

significant are at the five, rather than one, percent level. However, there is a statistically 

significant reduction in summer rainfall in all regions. East Scotland has experienced a 

significant nineteen percent decrease in summer rainfall since 1914. Precipitation has 

increased in North and West Scotland in all other seasons although the only trend that is 

statistically significant is the more than twenty percent increase in West Scotland in spring. 

Annual mean precipitation has increased across most of Scotland since 1914, and, with the 

exception of the summer season, rainfall has increased in all regions. The exception to this is 

the slight reduction of both annual mean and winter precipitation in East Scotland. This is the 

opposite of the trend calculated over more recent decades. These changes are not however 

significant, with the exception of the summer drying. Therefore, it is not possible to say 

definitively at this time whether there is a trend of long term drying in East Scotland and 

wetting over the rest of Scotland. 

The apparent contradiction between the two periods of data can be explained by looking at a 

time-series of annual mean total precipitation since 1914 (Figure 23). The full sequence of 

data from 1914 is shown. It can be seen that during the 1960s and 1970s the inter-annual 

variation in rainfall (particularly in the North and West regions) is quite low and the totals are 

also lower than in the earlier record. This is then followed by an increasingly wet period. This 

is why the analysis over the shorter period produces such large percentage changes in 

annual, and possibly winter, averages. The wet period in the 1980s may also account for why 

the drying trend in East Scotland over the 1914 to 2004 period is not seen in the shorter time 

period from 1961. It is apparent from the time-series data that East Scotland has a much 

drier climate than the other two regions. The high correlation between the North and West 

Scotland time-series indicate the two regions are likely to have a very similar rainfall 

climatology. This can be seen in Figure 24 which shows the 1961 to 1990 rainfall annual 

rainfall climatology for Scotland 12 . North and West Scotland have a wetter climate than 

eastern regions. This is to be expected given the presence of the Highlands, which provide a 

rain shadow effect for eastern areas, due to the prevailing westerly winds over Scotland. 

12 The 1971 to 2000 climatology is very similar and can be viewed on the Met Office website 

(http://www.metoffice.gov.uk/climate/uk/averages/index.html). 

25


Figure 23 - Annual precipitation amount (mm) for Scottish regions, 1914 to 2004, with 


2200 

2000 

Annual precipitation amount (mm) 

1800 

1600 

1400 

1200 

1000 

800 

600 

1914 

1918 

1922 

1926 

1930 

1934 

1938 

1942 

1946 

1950 

1954 

1958 

1962 

1966 

1970 

1974 

1978 

1982 

1986 

1990 

1994 

1998 

2002 




Figure 24 - Climatology of annual rainfall amount (mm) for Scotland, 1961 to 1990. 

Source: www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html 

The maps of spatial trends for each season are given in Figure 25. These trends have been 

calculated for the 1961 to 2004 period and therefore it must be remembered therefore that, in 

terms of long-term behaviour, they may be slightly misleading. It is however clear that the 

largest changes have occurred in winter months across all but the most eastern areas of 

Scotland. In some areas of the west Highlands and the Hebrides winter rainfall has more 

than doubled since 1961. The pattern of change is completely reversed in autumn with 

26


eastern areas being the only widespread region to become wetter, with increases in excess 

of twenty percent. In summer the east-west contrast of the changes shifts to produce pattern 

with more north-south variation. Northern areas of Scotland have become drier since 1961, 

particularly the north-west. This reduction in summer rainfall exceeds twenty percent in some 

locations. This is enhancing the strong seasonal cycle present in Scottish rainfall. Jones and 

Conway (1997) found no overall long-term trend in area-averaged annual precipitation for 

England & Wales or Scotland from 1766 to 1995, but did note a significant increase in winter 

precipitation, especially in Scotland since 1986, which agrees with these findings. 

Figure 25 - Gridded change for precipitation (%), based on a linear trend from 1961 to 

2004: a) spring, b) summer, c) autumn, d) winter. 

27


Days of intense or heavy rainfall, in this case defined as days of rainfall in excess of ten 

millimetres, have also changed. Table 9 shows the change calculated from a linear trend 

analysis. Due to availability of data for derived fields such as this, only the 1961 to 2004 

period has been analysed. As with total precipitation there is a significant trend of increasing 

heavy rainfall in winter months. North and West Scotland have seen an increase of more 

than eight days of heavy rainfall in a winter season. In all other seasons the changes are 

small and not significant. 

Table 9 - Changes in days of heavy rain ≥ 10 mm (days), 1961 to 2004. Statistically 


level) type. 

North 


East 


West 


Spring 1.8 1.0 1.6 1.5 

Summer -1.4 -0.5 0.9 -0.4 

Autumn -0.2 2.3 0.1 0.7 

Winter 8.3 3.5 8.2 6.7 

Annual 8.2 6.2 10.6 8.3 

A visual comparison with the time-series of annual mean total precipitation shows a high 

level of correlation (Figure 26). This implies that the years with highest total rainfall are also 

the years with the most days of heavy rainfall, and vice versa. 

Figure 26 - Annual days of heavy rain ≥ 10 mm for Scottish regions, 1961 to 2004, with 


80 

70 

Days of heavy rain 

60 

50 

40 

30 

20 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 

28 




It must also be remembered that although significant trends are identified for change in 

winter and annual mean number of days of heavy rainfall, the apparent high correlation with 

total precipitation implies that it may be reasonable to assume a similar behaviour before 

1961. This would imply that although recent winters have seen significantly more days of 

heavy rainfall that in a longer time-series of data the change may not be significant, given 

that the longer record also shows no significant increase in winter rainfall since 1914. This 

speculation shows that interpreting trends in relatively short records must be done with 

caution.


The spatial pattern of seasonal change in the number of heavy rainfall days (1961 to 2004) 

can be seen in Figure 27. The patterns of change are broadly similar to those for total 

precipitation with a strong east-west gradient in winter months. Although there has been little 

or no change in eastern Scottish regions, most of the west has seen a winter increase of 

more than five days of heavy rainfall. Changes in summer months are small and typically not 

significant. This is consistent with the findings of Osborn et al. (2000). They found, for the UK 

during 1961-1995, an increasing contribution of heavy rainfall events in winter compared to 

light and medium events, while the opposite occurred in the summer. The area in north-west 

Scotland, around Achnashellach has the largest change, with a reduction of up to ten days in 

spring, summer and autumn seasons. There are several stations in this region with different 

record periods that have been used in the data gridding process. This localised feature of 

decreasing number of heavy rains days is likely to be robust as more than one station’s data 

is being used. 

29


Figure 27 - Gridded change for days of heavy rain ≥ 10 mm, based on a linear trend 

from 1961 to 2004: a) spring, (b) summer, (c) autumn, (d) winter. 

A number of precipitation indices can be derived from observed data. These typically 

describe some aspect of the nature of precipitation within a year. A number of these indices 

have been calculated, and analysed for this report. Table 10 shows the results of analysis of 

the 1961 to 2004 precipitation dataset for three indices: 

• The maximum number of consecutive dry days (CDD) 13 , where a dry day is defined as a 

day with no more than 0.2 millimetres of rainfall. It should be noted that this is not an 

indicator of drought. Even in drought conditions an occasional day of rain may occur. 

13 Consecutive Dry Days = Maximum number of consecutive days with rainfall ≤ 0.2 mm 

30


• Rainfall intensity 14 . This is the average amount of rainfall which falls on a rainfall day. 

This only includes days when rainfall is greater than or equal to one millimetre and 

represents the average rainfall on such a day. 

• Maximum 5-day precipitation amount. This is a measure of the heaviest rainfall in a 5-day 

period for a year. 

Table 10 - Changes in annual precipitation indices, 1961 to 2004: a) maximum 

consecutive dry days (days), b) mean rainfall intensity on days with rain ≥ 1mm (%), c) 

maximum 5-day precipitation amount (%). Statistically significant trends are shown in 

bold (significant at the 1% level) or italic (significant at the 5% level) type. 

North 


East 


West 


Consecutive Dry Days (days) -0.2 1.1 0.1 0.3 

Rainfall Intensity (%) 7.4 7.6 7.8 7.6 

Maximum 5-day precipitation amount (%) 16.8 25.2 24.5 21.3 

Over the period 1961 to 2004 there has been very little change in the maximum number of 

consecutive dry days (CDD) in a year. Figure 28 shows a time-series of this index and it is 

clear that inter-annual variability is high. It is also clear that there is no discernable long-term 

trend in this index for this period. Years with the highest values of CDD in each region often 

coincide indicating a period of widespread dry weather. However, there are also many 

examples in the time-series when correlation between the regions is not high. 

Figure 28 - Annual maximum consecutive dry days for Scottish regions, 1961 to 2004, 


24 

22 

Consecutive dry days (days) 

20 

18 

16 

14 

12 

10 

8 

6 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

31 

2003 




There is a significant increasing trend in rainfall intensity in both East and West Scotland. 

There is a similar size of increase in North Scotland but the change is not significant as 

14 Rainfall Intensity = Total rainfall on raindays ≥ 1 mm divided by the number of raindays ≥ 1 mm.


natural variability in rainfall is higher in this region. This can be seen in the annual mean 

time-series shown Figure 29. There does not appear to be a high correlation between yearto-year 

rainfall intensity over the three regions, although the long-term trend (smoothed 

curve) is very similar. 

Figure 29 - Annual mean rainfall intensity (mm/day) for Scottish regions, 1961 to 2004, 

with smooth filter 

9.5 

9.0 

Rainfall intensity (mm/day) 

8.5 

8.0 

7.5 

7.0 

6.5 

6.0 

5.5 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




The most significant increases are in the maximum 5-day rainfall precipitation (see Table 10). 

The average increase since 1961 is over twenty percent. All increases are statistically 

significant at the one percent level. The year-to-year variation in this index for the period 

1961 to 2004 can be seen in Figure 30. Inter-annual variability is high and, with the exception 

of a few years, there is little correlation between regions. Values of the index are very similar 

in North and West Scotland, although a steadily increasing trend is clearly apparent in all 

regions. The lower rainfall totals of East Scotland are reflected in lower maximum 5-day 

averages. 

32


Figure 30 - Annual maximum 5-day precipitation amount (mm) for Scottish regions, 

1961 to 2004, with smoothed curve 

140 

Maximum five-day rainfall (mm) 

130 

120 

110 

100 

90 

80 

70 

60 

50 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




Spatial patterns of change for these three derived indices are shown in Figures 31 and 32. 

There is a clear east-west contrast in the change in number of consecutive dry days (Figure 

31). This pattern does not correlate well with any of the rainfall change patterns already 

presented, possibly indicating that the change is unlikely to occur predominantly in one 

particular season. Mapped trends of rainfall intensity and maximum five-day precipitation are 

shown in Figure 32. Both quantities increase for most of Scotland although there is a 

reduction for some northern and coastal location, including the Outer Hebrides, Orkney and 

Shetland Islands. 

Figure 31 - Gridded change for annual maximum consecutive dry days (days), based 

on a linear trend from 1961 to 2004 

33


Figure 32 - Gridded change (percentage) for a) annual rainfall intensity on days with ≥ 

1 mm rainfall, and b) annual maximum 5-day precipitation amount, based on a linear 


2.4. Snow and frost 

Some aspects of snow variability and change are captured in precipitation variables 

discussed previously. For example, the liquid equivalent of any snow that falls in a day is 

added to any rainfall measured to provide a total precipitation figure in millimetres per day. 

The length of the snow season is another measure that is often used. Meteorological 

observing stations record the state of the ground at 0900 hrs, i.e. 9 o’clock GMT, and from 

this a measure of the number of days with snow lying on the ground can be derived. It is 

recorded that snow is lying if more than fifty percent of the ground is covered with snow. This 

index does not equate to the length of the snow season but it is a good indictor of it. Table 11 

shows the percentage change in the number of days of snow cover for Scotland and the 

three regions since 1961. The analysis covers the three seasons when snow cover is likely to 

occur, i.e. summer is excluded. 

Table 11 - Changes in days of snow cover (percentage), 1961/62 to 2004/05. Statistically 


level) type. 


Scotland Scotland Scotland Scotland 

Spring -28.0 -27.5 -44.6 -31.0 

Autumn -70.9 -66.8 -82.6 -71.7 

Winter -25.9 -31.8 -36.9 -30.2 

Annual -28.8 -31.6 -40.7 -32.1 

Over the last forty years, the number of days of snow cover has decreased in each region 

and in all seasons. In winter the decreases are greater than twenty five percent, and are the 

largest absolute changes, a decrease of 7 days. The largest percentage changes have 

occurred in spring and autumn, indicative of a shortening of the snow season. In autumn the 

34


decreases in each region are large, greater than seventy percent in North and West 

Scotland, and statistically significant. Climatology shows that the average number of days of 

snow cover in autumn is low (see Figure 33, lower panel) so even a large percentage change 

results in a relatively modest reduction of days. It is likely that the autumn reduction is due to 

the snow season beginning later in the year. In spring there are also large percentage 

decreases. The average number of days of snow cover in spring is however greater than in 

autumn (see Figure 33, upper panel). This springtime reduction again indicates that the 

season is likely to come to a close earlier in the year than previously. This reduction in the 

length of the snow season is probably due to the temperature increases discussed in Section 

2.2. 

Figure 33 - Climatology of number of days of snow cover for Scotland, 1961 to 1990. 

Spring (March, April and May) is shown in the upper panel, autumn (September, 

October and November) in the lower panel. 

Source: www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html 

35


As noted above, for a day to be recorded as having snow cover more than fifty percent of the 

ground must be covered in snow. This is calculated for each year from August to July so that 

the snow season is not split. Time-series of number of days of snow cover in a year is shown 

in Figure 34. Inter-annual variability in the three regions is highly correlated. The decreasing 

trend is apparent in all regions, with North and East Scotland seeing a reduction from a 

typical thirty-five days of snow cover a year in the 1960s to an average twenty-six days per 

year in present climate. Over the same period, the number of days of snow cover in West 

Scotland has reduced from an average twenty per year to just thirteen. The time-series also 

highlight a number of years with a particularly long season of snow, such as the winter of 

1962/63 and 1978/79. 

Figure 34 - Annual days of snow cover for Scottish regions, 1961/62 to 2004/05, with 


80 

70 

Annual days of snow cover 

60 

50 

40 

30 

20 




10 

0 

Jul-62 

Jul-64 

Jul-66 

Jul-68 

Jul-70 

Jul-72 

Jul-74 

Jul-76 

Jul-78 

Jul-80 

Jul-82 

Jul-84 

Jul-86 

Jul-88 

Jul-90 

Jul-92 

Jul-94 

Jul-96 

Jul-98 

Jul-00 

Jul-02 

Jul-04 

A day of air frost is defined to be a day with minimum air temperature of less than 0°C. As 

with snow cover, the analysis of air frost is restricted to the seasons where air frost is likely to 

occur, i.e. summer is excluded. Analysis of change, based upon linear trends over the period 

1961 to 2004, is presented in Table 12. A substantial reduction in the number of days of air 

frost in all seasons and in each of the three regions is clearly apparent. Since 1961 there has 

been more than a twenty-five percent reduction in the number of days of air frost annually, a 

change that is statistically significant in all three regions and nationally. As with snowfall, 

although changes in winter are the largest in absolute terms (decrease of 10 days), it is the 

spring and autumn seasons that show the largest percentage changes and most significant 

trends. This is consistent with the warming trend discussed earlier and the lengthening of the 

growing season. 

Table 12 - Change in days of air frost (percentage), for 1961/62 to 2004/05. Statistically 


level) type. 

North Scotland East Scotland West Scotland Scotland 

Spring -30.5 -29.0 -29.2 -29.7 

Autumn -33.5 -31.3 -33.7 -32.8 

Winter -20.1 -21.3 -24.7 -21.7 

36


Annual -25.7 -25.1 -27.7 -26.0 

Time-series of annual days of air frost (Figure 35) provide further evidence in support of this 

as the peaks in years with higher number of days of air frost coincide with years having later 

start in the growing season (Figure 13). As the calculation of annual days of air frost is offset, 

i.e. calculated from August to July rather than January to December, it is not possible to 

directly compare the years of low occurrence of days of air frost with those of high annual 

temperatures. However, a visual comparison of Figures 3 and 35 indicates that there is a 

level of consistency between the two time-series. 

Figure 35 - Annual days of air frost for Scottish regions, 1961/62 to 2004/05, with 


120 

110 

100 

90 

80 

70 

60 

50 

40 

30 

Jul-62 

Jul-64 

Jul-66 

Jul-68 

Jul-70 

Jul-72 

Jul-74 

Jul-76 

Jul-78 

Jul-80 

Jul-82 

Jul-84 

Jul-86 

Jul-88 

Jul-90 

Jul-92 

Jul-94 

Jul-96 

Jul-98 

Jul-00 

Jul-02 

Jul-04 

Annual days of air frost 




Ground frost, which occurs when the grass minimum temperature reaches 0°C or below, is a 

common occurrence in Scotland, even in the summer. Since 1961 there has been a 

decreasing trend in the number of days of ground frost in all seasons, and each of the three 

Scottish regions (see Table 13). The decreasing trend is significant in the spring, especially 

for North and East Scotland. When the seasons are combined and the trends recalculated 

for each year the decrease in number of ground frost days in an average year is significant at 

the one percent level. Figure 36 shows that a steady decline in the number of days of ground 

frost each year began in the 1980's. 

Table 13 - Changes in days of ground frost (percentage), 1961/62 to 2004/05. 

Statistically significant trends are shown in bold (significant at the 1% level) or italic 


North 


East 


West 


Spring -11.4 -8.7 -7.5 -9.4 

Summer -3.0 -1.8 -1.4 -2.2 

Autumn -7.8 -4.1 -4.3 -5.6 

Winter -8.2 -8.4 -9.8 -8.7 

Annual -31.8 -25.2 -25.2 -27.8 

37


Figure 36 - Annual days of ground frost for Scottish regions, 1961/61 to 2004/05, with 

smoothed curve. 

180 

170 

Annual days of ground frost 

160 

150 

140 

130 

120 

110 

100 

90 

80 

1962 

1964 

1966 

1968 

1970 

1972 

1974 

1976 

1978 

1980 

1982 

1984 

1986 

1988 

1990 

1992 

1994 

1996 

1998 

2000 

2002 

2004 




The number of days of air frost and snow cover are typically calculated as annual values. 

The trends in the gridded datasets of these quantities are mapped for 1961 to 2004 in Figure 

37. The percentage changes in both quantities are typically greatest for the Scottish islands 

or in areas close to the coast. The proximity of the sea has a moderating effect on 

temperatures in these regions so days of frost or snow cover are less common than for areas 

further inland. This means that a relatively small increase in temperature, resulting in a small 

reduction in these cold weather phenomena, will have a larger proportional impact. For this 

reason the spatial patterns of change in Figure 37 are presented in terms of numbers of days 

rather than as a percentage. Although the overall changes described in this section are 

largely reductions it should be noted that in some localised areas there has been an increase 

in the number of days of snow cover, particularly in northern mainland Scotland. 

38


Figure 37 - Gridded change for annual days of air frost and days of snow cover (days), 

based on a linear trend from 1961 to 2004. 

For this study, the analysis of ground frost has been extended to look at seasonal rather than 

annual patterns of change. Figure 38 shows the spatial detail of these trends. While there 

has been a trend of decreasing occurrence of ground frost for most areas in all season, there 

has been little change on the Orkney and Shetland Islands. In fact, the number of days of 

ground frost have actually increased in winter on both the Shetland and Orkney Islands. The 

decreasing frequency of occurrence of ground frost has been especially marked over the 

western Highlands and Hebrides in spring. 

39


Figure 38 - Gridded change for days of ground frost (days) based on a linear trend 

from 1961 to 2005; a) spring, b) summer, c) autumn, d) winter. 

As with growing season gridded datasets of the start and end of the frost free season do not, 

as yet, exist. An analysis can however be completed on the records from individual observing 

sites. Analysis of the dates of occurrence of the first ground frost from August 1st and the last 

ground frost before the end of July at four Scottish stations 15 has revealed that the length of 

15 Threave near Castle Douglas in Dumfries and Galloway, Blythe Bridge near Peebles in the Scottish Borders, 

Wick in the Highlands and Kinloss in Moray. Threave and Blythe Bridge are inland stations at altitudes of 70m 

and 250m respectively, while Wick and Kinloss are low-lying coastal stations. 

40


the frost-free season has extended, by between 20-40 days (Table 14). At each of the 

stations, the first frost is occurring later, but the more significant and rapid change is seen in 

the date of the last frost, which has become between 12-24 days earlier since 1961. 

However, as can be seen in Figures 39 and 40, there is very high inter-annual variability in 

the first and last frost occurrence dates, and summer frosts are still common at each of the 

four sites. 

Table 14 - Changes in the dates of the first and last ground frost, in days starting from 

1 st August, and changes (days) in the length of the frost-free season spanning 31 st 

July – 1 st August, for four Scottish stations over the period 1961 to 2005. 

Threave 

Blythe 

Bridge Kinloss Wick 

First ground frost 3.4 10.2 7.3 11.8 

Last ground frost -22.5 -15.0 -12.1 -24.0 

Frost-free season 29.1 24.5 20.0 38.8 

Figure 39 - Date of the first ground frost in days from the 1 st August, 1960 to 2005, at 

four Scottish stations, with smoothed curve. 

100 

90 

First ground frost (days from 1st August) 

80 

70 

60 

50 

40 

30 

20 

10 

0 

1960 

1962 

1964 

1966 

1968 

1970 

1972 

1974 

1976 

1978 

1980 

1982 

1984 

1986 

1988 

1990 

1992 

1994 

1996 

1998 

2000 

2002 

2004 

Threave 

Blythe Bridge 

Kinloss 

Wick 

41


Figure 40 - Date of the last ground frost before the end of July, in days from the 1 st 

August, 1961 to 2005, at four Scottish stations, with smoothed curve 

370 

360 

Last ground frost (days from 1st August) 

350 

340 

330 

320 

310 

300 

290 

280 

270 

260 

2.5. Sunshine 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 

2005 

Threave 

Blythe Bridge 

Sunshine records are some of the longest duration meteorological kept in the UK. A dataset 

has been created, and analysed, which includes data from 1929. As previously, the analysis 

of these data is presented alongside the shorter 1961 to 2004 period that is being used as 

the benchmark for this study. The average number of sunshine hours in a day has increased 

by a small percentage annually in all three regions however there is no clear overall pattern 

of change with some seasons and regions seeing more sunshine and others less (Table 15). 

One signal though is clear: since 1961 the autumn months have been sunnier. This is true in 

all three regions. Although the changes are greater than ten percent they are not statistically 

significant and may therefore be due to natural variability. East Scotland has become sunnier 

in all seasons since 1961 but again the change is not statistically significant. Over the longer 

period, i.e. since 1929, patterns of change are different but there are some significant trends. 

These occur in North Scotland in winter and the annual mean. Although these changes are 

modest, less than a six percent reduction in the annual mean, they are statistically significant 

and therefore beyond the range expected from natural variability. The number of hours of 

sunshine have decreased, to varying degrees, in all seasons in North Scotland since 1929. 

Table 15 - Changes in total sunshine hours (%), 1961-2004 and 1929-2004. Statistically 


level) type. 

1961-2004 1929-2004 




Spring 4.5 6.9 2.7 4.7 -5.6 0.5 -4.4 -3.3 

Summer -2.1 0.2 -1.4 -1.1 -3.1 1.1 1.9 -0.2 

Autumn 17.9 12.1 11.0 13.8 -3.0 4.5 8.3 2.8 

Winter -4.6 12.8 -0.6 2.6 -13.8 -0.4 -0.3 -5.1 

Annual 2.7 5.5 1.6 3.3 -5.6 1.2 0.2 -1.6 

Kinloss 

Wick 

42


The average number of hours of sunshine recorded each day is lowest in North Scotland but 

this is also the region that has seen some of the largest changes. This is demonstrated by 

the regional time-series since 1929, shown in Figure 41. The time-series and seasonal 

trends indicate a complex pattern of changing sunshine hours. There is a high level of 

correlation between inter-annual variability of annual means for the regions but this masks 

differences between the regions at a seasonal timescale. The wide spatial variation is 

apparent in Figure 42, which shows the patterns of change in sunshine for each season for 

the 1961 to 2004 period. The same colour scale is used for each season. This means that is 

it easy to see that there has been only slight change over this period in either spring or 

summer and that the main changes have occurred in the second half of the year. It must be 

noted that the maps show change in sunshine hours as a percentage, and, as daylight hours 

are lowest in winter it requires a smaller absolute change to result in a relatively large 

percentage change. However, in some areas the changes are large, e.g. up to a forty 

percent reduction in sunshine hours in winter (December-February) in parts of North and 

West Scotland. In many cases these areas are also the ones seeing the largest percentage 

increases in autumn months (September-November). As the patterns are highly localised 

these changes are not apparent in the regional and national averages. 

Figure 41 - Annual sunshine hours for Scottish regions, 1929 to 2004, with smoothed 

curve. The vertical dashed line marks the position of 1961. 

1600 

1500 

Annual sunshine hours 

1400 

1300 

1200 

1100 

1000 

900 

800 

1929 

1932 

1935 

1938 

1941 

1944 

1947 

1950 

1953 

1956 

1959 

1962 

1965 

1968 

1971 

1974 

1977 

1980 

1983 

1986 

1989 

1992 

1995 

1998 

2001 

2004 




43


Figure 42 - Gridded change for sunshine, based on a linear trend from 1961 to 2004: a) 

spring, b) summer, c) autumn, d) winter. 

The east-west contrast in the winter change pattern is reminiscent of some of the patterns 

already seen. As would be expected, there is a strong similarity with patterns of change in 

rainfall. It would be logical to assume a similar pattern of change for cloud cover. This is 

discussed below in section 2.6 

44


2.6. Cloud 

Although the dataset employed in this study includes cloud cover, there is a point of caution 

to be made when the data are analysed. The records of cloud cover cannot be considered 

homogeneous. In particular, there has been a large scale move to automated observing 

methods over recent years, which has resulted in possible inconsistencies between records. 

Table 16 shows seasonal trends in cloud cover for each of the regions, calculated for the 

1961 to 2004 period. None of the trends identified are statistically significant. 

Table 16 - Changes in percentage cloud cover, 1961 to 2004. Statistically significant 

trends are shown in bold (significant at the 1% level) or italic (significant at the 5% level) 

type. 

North 


East 


West 


Spring -0.73 -0.69 -0.56 -0.67 

Summer -0.02 0.06 -0.64 -0.17 

Autumn -0.57 0.55 1.00 0.24 

Winter -1.98 -2.15 0.02 -1.45 

Annual -0.90 -0.43 0.26 -0.42 

Recording methods for hours of sunshine and cloud cover mean that there is no direct 

relationship between the two. However, it is reasonable to assume some degree of 

correlation. Visual comparison of the change in sunshine hours presented in Table 15 with 

cloud cover change in Table 16 shows that this is not the case. It is also possible that a level 

of correlation exists between changes in cloud cover and precipitation or diurnal temperature 

range, but the cloud cover changes presented here appear uncorrelated with these variables. 

It may be that the changes in cloud cover are not statistically significant and natural variability 

is dominating any underlying trend but it is much more likely to be indicative of the difficulties 

in comparing records based upon differing observing methods. The time-series of cloud 

cover for each region is shown in Figure 43. The large decrease in recent years is likely to be 

due to the change in observing methods. 

Figure 43 - Annual percentage cloud cover for Scottish regions, 1961 to 2004, with 


80 

78 

76 

Cloud cover (%) 

74 

72 




70 

68 

66 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

45 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003


It is clear from the time-series that identifying a trend in existing data using the current 

method is not possible due to the inconsistencies in the data records. Given the possible 

problems with the dataset any spatial patterns of change are likely to be misleading and 

hence, mapping of any trends in cloud cover has not been included in the analysis presented 

here. 

2.7. Mean sea level pressure 

Large-scale pressure patterns dictate the many aspects of Scottish weather. Low pressure 

systems pass across the country bringing weather that is predominantly wet and windy while 

high pressure is associated with less changeable and often drier conditions. The positioning 

of centres of high and low pressure determines the flow of air across Scotland and the type 

of weather experienced. The difference, or gradient, of pressure between the north and south 

of the country is related to mean wind speeds. The long-term average of this gradient, 

particularly in winter, is also linked with the North Atlantic Oscillation (NAO). 

The change in seasonal and annual average mean sea level pressure since 1961 is shown 

in Table 17. Change is presented in terms of hectopascals (hPa), where one hectopascal is 

equivalent to one millibar. Given that the average mean sea level pressure for Scotland is 

approximately 1012 hPa it is clear that observed changes are low, much less that one 

percent. Year to year variation is high, as can be seen by the time-series presented in Figure 

44. Correlation between the three regions is also high, consistent with the large-scale natural 

of pressure patterns. 

Table 17 - Changes in mean sea level pressure (hPa), 1961 to 2004. No trends are 

statistically significant trends at either the 1% or 5% level. 

North 


East 


West 


Spring 0.2 0.5 0.5 0.3 

Summer -0.4 -0.4 -0.6 -0.4 

Autumn -0.5 -0.6 -0.9 -0.6 

Winter -2.6 -1.7 -1.3 -1.9 

Annual -0.8 -0.5 -0.5 -0.7 

46


Figure 44 - Annual mean sea level pressure (hPa) for Scottish regions, 1961 to 2004, 


1016 

1015 

Mean sea level pressure (hPa) 

1014 

1013 

1012 

1011 

1010 

1009 

1008 

1961 

1963 

1965 

1967 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 




Table 17 and Figure 44 show that although mean sea level pressure is a large-scale 

variable, analysis of seasonal and regional averages is not necessarily the most informative 

analysis technique. Figure 45 shows mapped trends since 1961 calculated from the gridded 

dataset for the summer and winter season. The summer map indicates that there is no 

consistent pattern of change but in winter months a pattern is clearly discernable. Average 

winter pressures have been falling in northern Scotland, particularly over the Outer Hebrides, 

Orkney and Shetland Islands, over the period 1961 to 2004. At the same time, there has 

been little change to average winter mean sea level pressure in southern Scotland. Given 

that the area north of Scotland is predominantly one of low pressure (i.e. the so-called 

Icelandic low) this implies that low pressures have become lower and that that the average 

winter pressure gradient across Scotland has increased since 1961, although it has to be 

noted that the change is small and unlikely to be significant. 

47


Figure 45 - Gridded change for annual average mean sea level pressure (hPa), based 

on a linear trend from 1961 to 2004: a) summer quarter, b) winter quarter 

An increasing north-south pressure gradient is consistent with trends in the North Atlantic 

Oscillation (NAO) over the same period. In the early 1960’s the NAO index was at a record 

low meaning that the pressure gradient over Scotland and the UK was reduced. Since that 

time it has, on average, risen thereby increasing the pressure gradients again. When the 

NAO index is high, winter storm tracks are shifted south with storms potentially tracking 

across England and Wales with more frequency than Scotland. Analysis of pressure 

observations from across the UK and Iceland (1957 to 2003), undertaken by Alexander et al 

2005, has shown evidence of a southwards move of the North Atlantic storm track. It is not 

possible to say whether the winter trend patterns mapped in Figure 45 are a direct result of 

recent trends in the NAO but they are consistent with it. 

2.8. Wind 

Observations of wind speed and direction can be very site dependent. For instance, there will 

be a marked difference between an observation in a mountain valley compared to one taken 

on flat arable land at the same moment in time. If the measuring instrument is moved on the 

observing site, buildings are erected in the vicinity or a site is relocated there will be an 

impact on the characteristics of wind observations at that location and the record will not be 

homogeneous. Although a gridded dataset of mean wind speed exists there are concerns 

about its use. Analysis has identified significant decreasing trends in the gridded dataset. It is 

thought that these trends are likely to be a result of inhomogenities in the station data rather 

than evidence of changes in the variable. For this reason the gridded dataset is not mapped 

here, instead records taken directly from three observing sites, where records are known to 

be reliable, are analysed. 

Time-series of annual mean wind speeds since 1957 are shown in Figure 46. One observing 

site from each of the three regions is used. Data are shown for Lerwick, Tiree and Leuchars. 

It is noted that all three sites are in coastal locations but the variation in wind at each site 

should be indicative of any long term trends. It must also be noted that prior to 1969 values 

for Leuchars are estimated from Turnhouse. It is apparent that inter-annual variability is low 

48


at each location and that no large scale trend influences all three. There are similarities 

between the time-series for Tiree and Leuchars, both of which show a trend of decreasing 

mean wind speeds in recent decades, however Lerwick has seen a trend of increasing wind 

speeds over the same period. 

Figure 46 - Annual mean wind speed (knots) for three Scottish stations; Lerwick, Tiree, 

and Leuchars (values estimated from Turnhouse prior to 1969), 1957 to 2004, with 


17 

16 

15 

Mean wind speed (knots) 

14 

13 

12 

11 

10 

9 

8 

7 

Lerwick 

Tiree 

Leuchars 

1957 

1960 

1963 

1966 

1969 

1972 

1975 

1978 

1981 

1984 

1987 

1990 

1993 

1996 

1999 

2002 

For comparison, Figure 47 shows time-series of the same quantity, annual mean wind 

speed, calculated from the gridded dataset. The three regions are shown as before. The 

anticipated decreasing trend is clear however the trend is very similar in all three regions and 

produces a larger decrease than is seen in the individual station records (Figure 46 above). 

This is not to say that the trends shown in Figure 47 are incorrect but that the gridded wind 

dataset requires further investigation before these possible inconsistencies can be explained. 

Figure 47 - Annual mean wind speed (knots) for Scottish regions, 1969 to 2004, with 


16 

15 

Mean wind speed (knots) 

14 

13 

12 

11 




10 

9 

1969 

1971 

1973 

1975 

1977 

1979 

1981 

1983 

1985 

1987 

1989 

1991 

1993 

1995 

1997 

1999 

2001 

2003 

49


One of the variables that can be derived from observed wind data is a measure of the 

number of days in a year that can be considered a day of strong wind. In this report, the 

measure used is that of a gale day, defined to be a day with mean wind speed of 34 knots or 

more over any 10-minute period. The exposed island locations of Lerwick and Tiree 

experience a higher number of gale days in a year than Leuchars (Figure 48). Inter-annual 

variability is also higher for the island locations but there is no clear trend in any of three 

records. 

Figure 48 - Annual days of gale for three Scottish stations; Lerwick, Tiree, and 

Leuchars, 1957 to 2004, with smoothed curve 

70 

60 

50 

Annual days of gale 

40 

30 

20 

10 

0 

1957 

1960 

1963 

1966 

1969 

1972 

1975 

1978 

1981 

1984 

1987 

1990 

1993 

1996 

1999 

2002 

Lerwick 

Leuchars 

Tiree 

50


3. FUTURE CHANGE IN SCOTTISH CLIMATE 

Global climate models (GCMs) are currently the only scientific tool available for predicting 

realistic patterns of current and future changes in climate and, in particular, the large scale 

patterns of change. These models require a large computing resource and hence are run at 

relatively coarse resolution. For example, the current global climate model at the Met Office’s 

Hadley Centre, called HadCM3, represents the British Isles with a horizontal resolution of 

approximately 300km which means that only two grid squares cover Scotland. For greater 

detail, and for impact studies, higher resolution regional models can be ‘embedded’ within 

the GCM grid. The version of the Hadley Centre regional model used to produce the 

UKCIP02 scenarios, HadRM3, has a horizontal resolution of 50km. The regional model 

projections show much more detail than the global model and is able to better represent 

extremes. Regional models are better able to capture extreme weather because not only can 

they represent smaller scale weather features but they also have a much better 

representation of orography. For example, the mountains of Scotland cannot be represented 

in the global model at all but the 50km RCM permits the mountains of Scotland to be partially 

resolved which results in increased spatial variation of rainfall. 

Every climate model, global or regional, produces a wealth of data. To achieve maximum 

value this data must be used in the context of the uncertainties (outlined in Appendix 2), and 

it must also be remembered that not all climate model data have been validated against 

observed climate. However, the large array of modelling studies which have been completed, 

and published, increase confidence and our understanding of model predictions and areas of 

uncertainty. 

In 2002 the UK Climate Impacts Programme published the latest set of Climate Change 

Scenarios for the United Kingdom (UKCIP02, Hulme et al, 2002). The climate model results 

contained within this report were from the Met Office’s Hadley Centre, based upon findings 

from the latest regional climate model, HadRM3. Following the approach used by the 

Intergovernmental Panel on Climate Change (IPCC) the UKCIP02 report presents a range of 

scenarios of change, based upon a range of possible emissions scenarios (termed ‘low’, 

‘medium-low’, ’medium-high’ and ’high’), all of which can be considered equally likely to 

occur. Results were presented for three ‘time-slices’ or thirty year periods centred about the 

2020s, 2050s and 2080s. 

It has to be recognised that UKCIP02 scenarios are based upon the projections of one 

regional climate model. While the UKCIP02 report presented the latest scientific 

understanding and modelling results for Scotland there are a number of sources of 

uncertainty (due to emissions scenarios, scientific uncertainties and natural variability), which 

should be borne in mind when interpreting the projected future Scottish climate. These 

uncertainties, discussed in Chapter 7 of UKCIP02, are summarised briefly in Appendix 2. 

Some of these uncertainties account for the differences between the 1998 and 2002 UKCIP 

reports and the Regional Climate Change Scenarios for Scotland report (Hulme et al, 2001). 

3.1. Observed trends in Scottish climate: the UKCIP02 context 

3.1.1. Temperature 

Irrespective of emissions scenarios or time-slice, temperatures are expected to rise over 

Scotland, with increases being greatest during summer and autumn months when a warming 

of up to 4.0°C (with the medium-high emissions scenario of forcing) is expected over parts of 

Scotland by the end of the century. Southern Scotland is projected to warm at a faster rate 

than the north. The patterns of change identified in observed temperatures broadly agree 

with this, particularly the geographical variation in rates of warming, seen clearly in winter 

months (Figures 4, 7 and 8). The projected warming in autumn months is not seen in the 

mapped trends for the 1961 to 1990 period. However, the longer 1914 to 2004 period, shown 

in Table 2, does indicate some of the largest temperature trends in the last ninety years are 

51


during the autumn season. During the longer period the warming is least in the North, again 

consistent with the expected patterns of future warming. 

In the UKCIP02 scenarios diurnal temperature range is expected the increase the most in 

summer with a complex pattern of smaller increases and decreases in other seasons. This 

pattern of change is not seen in the analysis of observed temperatures. Over recent decades 

there has been little change to the diurnal temperature range in summer and it has actually 

increased in all other seasons, particularly winter. 

By the 2080s heating degree days are projected to decrease by fifteen to forty percent. The 

changes are likely to be greatest in southern and eastern Scotland. The pattern of change 

from the analysis of observed variables is consistent with this. By the same time, growing 

season length is expected to have increased by thirty to ninety days. An extended growing 

season is also identified in the observed dataset although the geographical pattern of change 

is different to that projected. However, the degree of change seen over the last century is 

comparable with that projected for this century. 

3.1.2. Precipitation 

Projected changes in precipitation across Scotland are more complex than those for 

temperature. Although there is expected to be relatively little change to annual rainfall 

amounts it is expected that winter months will become wetter, while summers months will be 

drier than at present. The pattern of change is not uniform, with eastern Scotland 

experiencing the most extreme percentage changes in precipitation, with a winter increase 

and a summer decrease. Changes are projected to be relatively small for all regions during 

the other seasons. Section 2.3 described the observed trends in Scottish rainfall. Since 1961 

there has been a significant increase in winter rainfall, which is consistent with climate model 

projections. However, there has also been an increase in the annual mean and little change 

during summer. As with the trends of temperature change, there are similarities between the 

precipitation trends over the longer 1914 to 2004 period and the projected future trends. Over 

the longer period, the summer months have become drier and there has been relatively little 

change to the annual mean values. 

The one aspect of the observed patterns of change in precipitation that is not consistent with 

the UKCIP02 scenarios is the spatial detail. East Scotland has seen the smallest increases in 

winter precipitation and some areas within this region have even become drier in winter since 

1961. This is contrary to the pattern expected from the climate change projections. However, 

the summer drying is consistent with observed trends since 1914. It is possible that recent 

changes are a result of natural variability and masking any underlying impact of climate 

change. It is interesting to note that one of the major differences between UKCIP02 and its 

predecessor UKCIP98 was the projected change to seasonal precipitation over Scotland. 

This analysis highlights that there are many uncertainties in the predictions of climate change 

for Scotland and that both observed and projected trends required care in their interpretation. 

Within the context of the UKCIP02 scenarios, it is likely that the intensity of rainfall will 

increase in winter months. An east-west contrast in change is expected, with the most 

extreme changes occurring in eastern Scotland. This geographical contrast is apparent in 

each of the scenarios presented in UKCIP02. However, the pattern has not been seen in the 

analysis of measures intense of heavy rainfall within the observed dataset, although the 

measures are not directly comparable with those used in UKCIP02. It is clear that since 1961 

heavy rainfall has increased across Scotland during winter months and that both rainfall 

intensity and maximum five-day rainfall have increased significantly. 

52


3.1.3. Snowfall 

Projections of future climate indicate that it is also likely that snowfall will decrease 

significantly. Winter snowfall may be reduced by fifty percent or more across Scotland by the 

2080s (UKCIP02, medium high scenario). The most pronounced projected changes are over 

eastern Scotland, with a potential decrease of over ninety percent. Again, it is not possible to 

compare the UKCIP scenarios directly with the variable analysed here but it is clear that the 

decreasing trend in observed snow cover is consistent with the climate change prediction 

although it is currently West Scotland that has experienced the greatest reduction in snow 

cover. 

3.1.4. Sunshine 

A measure of sunshine hours was not included in the UKCIP02 scenarios, so it is not 

possible to compare observed trends with those projected for the future. Cloud cover was 

considered although problems with the gridded dataset, as described in section 2.6, make 

the results of analysis uncertain. By the 2080s cloud amounts are expected to increase 

slightly in winter, particularly in the northern half of Scotland, and to decrease in all other 

season, with the greatest changes occurring in summer months in southern and eastern 

areas. The observed reduction of winter sunshine hours is, to some extent, consistent with 

this. 

3.1.5. Mean sea level pressure 

Maps of change in mean sea level pressure were also not given in the UKCIP02 scientific 

report although it is commented upon in the text. Changes in spring and autumn are small. In 

winter the north-south pressure gradient increases resulting in stronger winds in southern 

and central Britain but little change in Scotland. Mean sea level pressure was used to 

investigate possible change in both North Atlantic storm tracks and the North Atlantic 

Oscillation (NAO). In the scenarios it was found that the storm track shifted southwards of 

their current position which resulted in strengthening winter winds across southern England. 

The NAO index was also expected to become predominantly positive indicating an increased 

north-south winter pressure gradient across Britain, consistent with more winters which are 

more ‘westerly”, i.e. milder, wetter and windier. The observed change in mean sea level 

pressure is broadly consistent with these projected future changes. 

3.1.6. Wind 

Future change in average mean wind-speed is highly uncertain. In the High emissions 

scenario, by the 2080s, a change of plus or minus five percent is typical. The values should 

be treated with caution given the uncertainties in modelling wind speeds. 

53


54


4. CONCLUSIONS 

A wide range of observed quantities have been analysed in this study and a complex picture 

of a changing Scottish climate has emerged. Some variables, such as temperature and 

precipitation, have a long record, which has enabled the more rapid changes of the last four 

decades to be put into the context of longer-term variation. It has also been shown that 

presenting a nationally averaged figure of change masks the fact that patterns of change are 

not uniform across Scotland or throughout the seasons. Difficulties in obtaining 

homogeneous datasets that can be gridded for mapping have also been highlighted, 

underlining the caution that should be exercised when interpreting some types of data. 

Significant increases in temperature have occurred in recent decades. These increases in 

temperature have been at a faster rate than at any other time in the ninety-year period 

considered in this study. Since 1961 spring and winter temperatures have increased at a 

faster rate in southern and eastern Scotland than in the northwest. In contrast when 

considering the longer ninety-year period it was found that average winter temperatures in 

northern Scotland are currently very similar to those recorded toward the start of the 1900s. 

This is even though annual mean temperatures have risen, fallen and then increased again 

over the same period of time. Since 1961 24-hour minimum temperatures (effectively nighttime 

minimum), have been increasing at a rate that is slower than day-time maximum 

temperatures, i.e. the diurnal temperature range has increased. This is contrary to the global 

trend for the period 1950 to 1993. When the Scottish data are considered over the longer 

1914 to 2004 period the relationship is reversed, and minimum temperatures increase at the 

faster rate, implying a decreasing diurnal temperature range. Given the different periods of 

time being compared it is not possible to say whether long term national, and local, diurnal 

temperatures ranges are changing in a different manner to the global average or not. 

The rate of change of both annual and winter mean precipitation has also been faster since 

1961 than at any other time in the 1914 to 2004 record. As with temperature records some 

aspects of the changes projected by climate models are only seen in the longer record. 

There are aspects of the spatial pattern of observed change, such as the wetter autumns and 

drier winters of Aberdeenshire, which are absent from the UKCIP02 future climate scenarios. 

The differences between future changes to seasonal rainfall patterns given by the UKCIP02 

scenarios and those of their predecessors are well known. Although the UKCIP scenarios 

are derived from models that are more scientifically complex than those of the earlier 

scenarios, none of the scenarios can be discounted. All are scientifically valid. The 

complexity of patterns of observed change and the variation in scenarios underlines the 

uncertainties associated with future regional precipitation changes. 

This study has shown that the use of a consistent dataset over a standard period of time, 

permits the interaction between certain variables to be seen clearly. For instance, the rises in 

temperature are linked to an increase in the length of the growing season. It has also been 

possible to use changes in one variable as supporting evidence for trends in another. For 

example, the fact that the last frost day of a year typically occurs earlier in spring now than 

previously supports the finding of an earlier start to the growing season. This consistency 

gives confidence in the identified trends. When trends appear to be inconsistent it may be 

that the relationship between variables is more complex than can be represented using this 

subset of data, which is based on one set of observing methods. It may also indicate a 

problem with the dataset, as is perhaps the case with cloud cover data. 

This study has focused upon the identification of trends in Scottish climate and, where 

possible, mapping the geographical patterns of these trends. The study does not seek to 

explain or attribute a cause to any of the changes. Many interesting features are identified 

that warrant further investigation but to do so is outside the scope of this study. However, 

55


what this study does is provide an up-to-data assessment of the changing climate in 

Scotland and a firm foundation for any party undertaking climate related work in Scotland. 

Many of the changes identified are consistent with the nature of change presented in the 

UKCIP02 scenarios. This is not to say that the changes identified can be attributed to 

anthropogenic climate change or that they are early indications of human impact on Scottish 

climate. In recent years it has become possible to discern changes in climate that cannot be 

attributed to natural causes but only at a spatial scale much larger than Scotland. While the 

similarities between observed and projected change are compelling, it is at this present time, 

not possible to tell whether local changes in Scottish climate are early indications of future 

climate change. What can be said with confidence is that the climate of Scotland has 

changed in recent decades. Where observed changes are comparable with those expected 

for Scotland it is now possible to point to the evidence that shows that Scotland has 

experience of what such changes mean and may therefore be better placed to plan 

adaptation measures for future climate change. 

56


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58


(Appendices) 

APPENDIX 1: SCOPING STUDY 

59


(Appendices) 

1. INTRODUCTION 

There is an increasing body of evidence, which shows that the climate of our planet is 

changing. Long records of observed data exist for specific locations however combining 

these separate records into gridded data sets is a relatively new innovation exploiting 

advanced spatial averaging techniques. Using such datasets to validate climate model 

simulations of observed climate has enabled scientists to say, with some level of confidence, 

that the changes which have been observed cannot be due to natural forcing alone and that 

man’s actions are contributing to global warming (IPCC, 2001). More recently it has become 

possible to say that regional patterns of change are also being influenced by man’s actions 

(Stott et al, 2003). 

In 2002 the UK Climate Impacts Programme published the latest set of Climate Change 

Scenarios for the United Kingdom (UKCIP02, Hulme et al, 2002). The climate model results 

contained within this report were from the Met Office’s Hadley Centre, based upon findings 

from the latest regional climate model HadRM3. his model was run for a ‘baseline’ period in 

order to represent present day climate, where present day climate was taken to be an 

average over the thirty-year period 1961 to 1990. In addition to the model representation of 

present day climate and the scenarios of future change, a database of gridded observed 

variables was constructed (See Hulme et al, Appendix 7). 

In recent years there have been a number of weather related events that have been linked in 

the media to climate change. While it is not possible to say whether any individual event is 

due to climate change it is possible to draw comparisons between current weather and how 

weather may be expected to change in the future. For example, the heat wave that impacted 

much of Europe in 2003 cannot, as a single event, be attributed to climate change. The 

temperatures reached are however comparable with the scenarios of an average summer by 

the middle of this century. 

There now exists a sometimes bewildering array of information relating to both the changes 

already observed in our climate and those which may be expected in the future. Figures of 

temperature change, either observed or projected, are often presented as average values on 

a global or national scale. There is no simple way for an individual in Scotland to find out 

what global warming and climate change mean in their region. The aim of this project is to 

address this need and to set a marker in time against which future changes may be 

examined. Therefore, we seek to collate readily available data in order to identify trends in 

the observed weather of Scotland and then to compare these with expected changes in 

future climate. 

60


(Appendices) 

2. DATA SOURCES 

There are four key sources for climate related data within the UK. Each provides access to 

readily available data, typically with a licence agreement and is either free of charge or will 

be supplied for a nominal fee to cover extraction and shipping. A licence is granted based 

upon certain criteria. The primary restriction is often that data is only provided for noncommercial 

applications or for academic research. A short description of each organisation 

and the data they supply is given below. Full conditions of data licensing are given on each 

organisation’s website. 

2.1 The Met Office 

The Met Office is a world-leading provider of environmental and weather-related services in 

the UK and around the world. In addition to providing the public with daily forecasts and 

warnings of high-impact weather the Met Office has a mandate to maintain an up-to-date 

climatological record of the UK, the National Meteorological Library and Archive. Historically 

weather observations have been recorded and stored on paper but increasingly these 

records are being transferred to digital media thus improving accessibility. 

The Met Office’s network of UK weather stations report a mixture of snapshot hourly 

observations of the weather known as synoptic observations, and daily summaries of the 

weather known as climate observations. Observations from around 200 UK synoptic stations, 

approximately 50 of which are sited in Scotland, are collected in real time; climate data from 

synoptic stations also comes in straight after readings are taken. This is supplemented by 

climate observations from several hundred co-operating observers which are submitted as 

collectives at the end of the month. All climate stations record daily maximum and minimum 

air temperature and rainfall amount, recorded over the period 0900-0900 period (1000-1000 

in summer). Many observe additional elements with synoptic stations recording a wide range 

of quantities. In addition there are around 5,000 rainfall stations in the rainfall network, 

approximately 1,000 being in Scotland. Maps of the locations of current synoptic, climate and 

rainfall recording sites in Scotland are available on the Met Office website 

(http://www.metoffice.gov.uk/climate/uk/networks/index.html). 

The station network provides a long record of weather observed at a series of individual 

locations. A sample of these (see Annex 1) are available from the Met Office website and 

can be downloaded free of charge. The Scottish locations available are Lerwick, Stornoway 

airport, Braemar, Tiree, Leuchars and Paisley. The data given are monthly means of 

• Mean maximum temperature 

• Mean minimum temperature 

• Mean grass minimum temperature 

• Total rainfall 

• Total sunshine duration 

The World Meteorological Organization (WMO) requires the calculation of averages for 

consecutive periods of 30 years, with the latest covering the 1961-1990 period. However, 

many WMO members, including the UK, update their averages at the completion of each 

decade, i.e. 1971 to 2000. Thirty years was chosen as a period long enough to eliminate 

year-to-year variations distorting the mean. These averages help to describe the climate and 

are used as a base to which current conditions can be compared. A selection of station, 

district and regional averages, or contoured maps, for a wide range of weather elements is 

available on the Met Office website (see Annex 1). The website also provides more 

information on the methods used to create the long-term averages and maps. 

61


(Appendices) 

In association with the UK Climate Impacts programme a number of gridded datasets have 

been developed by the Met Office. These data sets have been created for 26 weather 

parameters, based on the archive of UK weather observations held at the Met Office. For 

most parameters approximately 500 stations are used to create each grid; for rainfall 

approximately 3,500 stations are used. The regression and interpolation process used to 

obtain the 5 km grids alleviates the impacts of station openings and closures on homogeneity 

but the impacts of a changing station network cannot be removed entirely, especially in 

topographically variable areas. Full details of the techniques used to create the datasets are 

available on the Met Office website (http://www.metoffice.gov.uk). Available parameters are 

listed in Annex 1. 

2.2 British Atmospheric Data Centre 

The British Atmospheric Data Centre (BADC) is the Natural Environment Research Council's 

(NERC) Designated Data Centre for the Atmospheric Sciences. The role of the BADC is to 

assist UK atmospheric researchers to locate, access and interpret atmospheric data and to 

ensure the long-term integrity of atmospheric data produced by NERC projects. 

The BADC has substantial data holdings of its own but also provides information and links to 

data held by other data centres. The data held at the BADC are of two types: 

• Datasets produced by NERC-funded projects. 

• Third party datasets that are required by a large section of the UK atmospheric 

research community and are most efficiently made available through one location (e.g. Met 

Office and the European Centre for Medium Range Weather Forecasting (ECMWF) 

datasets). 

All BADC data are available on-line through a World Wide Web interface 

(http://www.badc.rl.ac.uk/) or via an ftp service. Software is provided to assist in the 

manipulation of the data and extensive information is provided on the data collection 

procedures, formats, data quality, contact names and references to journal papers. 

Since its establishment the BADC has become the main point of contact for UK researchers 

needing access to the meteorological products of both the Met Office and ECMWF. 

2.3 British Oceanographic Data Centre 

The British Oceanographic Data Centre (BODC), as a national facility for looking after and 

distributing data concerning the marine environment, has a range of roles and responsibilities 

which include: 

• The National Oceanographic Database. BODC maintains and develops the National 

Oceanographic Database (NODB). The NODB is a collection of marine data sets originating 

mainly from UK research establishments. 

• UK Tide Gauge Network. BODC manages the data for the UK Tide Gauge Network. 

The network records tidal elevations at 45 locations around the UK coast. It is part of the 

National Tide & Sea Level Facility (NTSLF). 

• The designated marine data centre for the Natural Environment Research Council 

(NERC). BODC is one of seven designated data centres that manage NERC's environmental 

data. 

The BODC holds a wealth of marine publicly accessible data collected using a variety of 

instruments and samplers and collated from many sources. It handles biological, chemical, 

62


(Appendices) 

physical and geophysical data and has databanks containing measurements of nearly 

10,000 different oceanographic variables. 

BODC encourages the use of its data holdings for science, education and industry, as well 

as the wider public and makes data available under a licence agreement. In the case of 

NERC data the conditions are in line with the NERC Data Policy that formally lays down the 

conditions under which the data may be used. For data from non-NERC organisations the 

conditions are broadly similar. Full details on data holdings and access are available on the 

BODC website (http://www.bodc.ac.uk/). 

2.4 UK Climate Impact Programme 

The UK Climate Impacts Programme (UKCIP) provides scenarios that show how our climate 

may change in coming decades and co-ordinates research on dealing with our future climate. 

UKCIP shares this information, free of charge, with organisations in the commercial and 

public sectors to help them prepare for the impacts of climate change. The UKCIP02 climate 

change scenarios datasets were produced by the Hadley Centre (Met Office) and Tyndall 

Centre, with funding from DEFRA, as a key component in UK national and regional climate 

impact assessments. It is strongly recommended that all potential users of the scenarios 

datasets read the accompanying UKCIP02 Scientific Report (Hulme et al, 2002) before 

proceeding with data analysis. 

UKCIP have constructed a Scenarios Gateway, a structured walk-through intended to be 

read in sequential order. Firstly, the "Maps" pages provide a visual representation of the 

results from the scenarios including additional material that could not be included in the 

report due to lack of space. They provide a reference to the range of data that has been 

extracted from the climate model. Further pages provide the essential information on how the 

scenarios were produced and thereafter on the different datasets that are available. 

Instructions on how to obtain a licence to become a registered user of the datasets can also 

be found on the website (http://www.ukcip.org.uk). 

Although the UKCIP scenarios are primarily associated with future change a baseline current 

climate dataset (1961 to 1990) is also available, based upon the regional model simulation of 

present day climate by the Hadley Centre regional climate model (HadRM3). The future 

climate fields are presented as changes relative to this baseline. All of the data is available at 

the 50km (HadRM3) grid-box scale in the form of monthly averages for the 2020s, 2050s and 

2080s time slices, where each time slice refers to a thirty year period, i.e. the '2020s' period 

refers to 2011-2040, the '2050s' period to 2041-2070, and the '2080s' period to 2071-2100. 

Further interpolation of some of the climate variables down to 5km has also been developed 

both for the time slices and the full time sequence from 2011 to 2100. Baseline data is 

available either as model simulated (50km) or based upon observations (5km) - in the latter 

case from the Met Office website. Full details are available on the UKCIP website 

(http://www.ukcip.org.uk). 

2.5 Climate change indicators 

A list of 34 Indicators of Climate Change in the UK was published in 1999 by Defra. More 

recently an expert meeting in March 2003 reviewed the set of indicators, see 

http://www.edinburgh.ceh.ac.uk/iccuk/. Only a limited number of the indicators include 

Scottish data. These include 

• Precipitation gradient across the UK, based upon the difference between a Scottish 

winter precipitation series and a SE England summer precipitation series. 

• The predominance of westerly weather, based upon a North Atlantic Oscillation index 

• River flows in northwest and southeast Britain 

63


(Appendices) 

• Frequency of low and high river flows in northwest and southeast Britain 

• Scottish skiing industry 

These indicators are based upon either point or aggregated data, rather than gridded 

datasets. Hence their ability to capture the spatial variation across Scotland is limited. Only if 

information from them is particularly relevant to this study will they be included. 

The usefulness of indicators should also be assessed in terms of other global changes that 

have accompanied climatic change, for example, land-use change. This makes disentangling 

the climate change signature for river-flow data difficult, as changes in stream-flow patterns 

will reflect a whole host of changes in land-use and catchment management practices as 

well. Future predictions of stream-flow will require rainfall-runoff modelling that is well beyond 

the scope of this project. 

64


(Appendices) 

3. ACCESS TO DATA 

Each of the data centres listed in section 2 holds archives of data which is both readily 

available and potentially relevant to this project. A summary of the parameters available is 

presented in tabular form in Annex 1. The datasets have been categorised as either gridded 

or point. Although this study is to focus upon gridded datasets it is considered beneficial to 

include data records for point locations. Similarly, although data used in the analysis of 

Scottish climate will be restricted to that which is readily available to the public or the project 

team, the listings in Annex 1 include some datasets that require a licence and are not free. 

This additional data has been included to benefit the reader, as these may prove useful 

supplementary information at a later date. 

It is recognised that the data lists presented in Annex 1 are not exhaustive but they do 

represent sufficient fields to describe Scotland’s climate and any trends in key parameters. 

Further datasets exist which are based upon model results, such as the UKCIP02 baseline 

climatology or ECMWF reanalyses. The tables in Annex 1 present only sources which have 

been derived from observed data and not that derived from models. There are also datasets 

which present climatologies which may be useful to the reader, such as the Flood Studies 

report (NERC, 1975) however these have also been excluded from the tables at this time. 

65


(Appendices) 

4. STAKEHOLDER VIEWS ON ADDITIONAL VARIABLES 

A brief email and telephone survey was undertaken of stakeholders in key sectors across 

Scotland. The survey provided a proposed list of derived variables to be included within the 

handbook and asked respondents which they would be interested in seeing and what 

aspects of those variables were most important to them. Initially 21 organisations/contacts 

were emailed and 11 responses by phone or email were received. Eight of these specifically 

indicated variables of interest and these include representatives from 8 of the 9 sectors 

contacted (tourism is absent). The full list of respondents is provided in Table 1 below. The 

list of organisations contacted is included in Annex 2. 

The number of respondents who selected each variable from the original list is shown in 

Table 2. Rainfall return periods was identified as being a key variable set to include in the 

handbook, with every respondent recognising the value of this to them. Cooling degree days 

and crop temperature sums were the least favoured variables, possibly reflecting a lack of 

familiarity in some sectors with these variables as well as no direct agricultural industry 

involvement. One respondent also emphasised the need to recognise the importance of 

micro-climate for agriculture and biodiversity. 

Table 1 – List of Respondents 

ORGANISATION 

NAME of RESPONDENT 

Scottish Executive 

Duncan Beamish 

Jennifer Hamilton 

Forestry Commission Steve Gregory 

SEPA 

Tim Jolley 

June Graham 

Rail track Scotland 

Andy Scobie 

NFU Scotland 

Craig Campbell 

COSLA 

Kathy Cameron 

Scottish Power 

Jane Telfer 

Scottish Water 

Annette Wilkinson 

RSPB 

Clifton Bain 

Stirling City Council 

Alan Speedie 

Dundee City Council 

Bryan Harris 

STEERING GROUP MEMBERS 

(CONTACTED FOR INFORMATION) 

SNIFFER 

Vanessa Kind 

SEPA 

Peter Singleton 

June Graham 

Scottish Executive 

Guy Winter 

Forestry Commission Helen McKay 

Scottish Natural Heritage Noranne Ellis 

Follow-up telephone calls were made to clarify what aspects of the variables and what 

threshold levels were important to them. However, it became apparent that most of those 

contacted could not readily provide further information on the importance of changes in the 

seasonality or threshold levels of the variables. This is not unexpected since the respondents 

are generally not scientists and their approach to this work is based more on anecdotal 

evidence of variable value rather than knowledge of significant thresholds. However, many 

respondents expressed interest in the handbook, even if they were unable to comment in 

66


(Appendices) 

detail on the variables relevant to them. The need to make the handbook readily accessible 

to non-scientists was stressed by several respondents. 

A number of additional variables were suggested by the respondents, since several of these 

were from the water sector, these include a number of water resource related datasets rather 

than pure climate variables: 

• Snow cover/ski season/snow patch records 

• Storm index/convective activity – i.e. measure of storm frequency/intensity 

• Runoff rates or river flow – Peak over threshold (POT) records, monthly means etc. 

• Groundwater level data 

• Spring flow records 

• Dates of first and last frosts of season 

• First flowering dates and other phenological information 

• Snow cover days 

• Wind speed 

Table 2 – number of respondents who selected each variable 

Variable 

Response 

rate 

Growing season lengths, + start and end dates 10/11 

Growing season intensity 10/11 

Other temp sums for key/indicative crops 8/11 

Soil moisture content or deficit /10/11 

PET (potential evapo-transpiration) 9/11 

Rainfall return periods 11/11 

Derived rainfall variables 10/11 

Frost days 10/118 

Heat wave duration 9/11 

Heating degree days 9/11 

Cooling degree days 8/11 

NAO index 10/11 

Sea level rise 10/11 

67


(Appendices) 

5. FUTURE CLIMATE CHANGE 

As stated earlier the aim of this project is to collate available observed data which describes 

the climate of Scotland and how it has changed over recent decades. Following the analysis 

of this data it is important to consider any identified trends within the context of the UKCIP02 

climate change scenarios. It is useful to be aware of other data which relates to scenarios of 

the future climate of Scotland. 

Global climate models are currently the only scientific tool available for predicting changes in 

climate and, in particular, the large scale patterns of change. These models require a large 

computing resource and hence are run at relatively coarse resolution. For example, the 

current Hadley Centre global model, HadCM3 represents the British Isles with a horizontal 

resolution of approximately 300km which means that only two grid squares cover Scotland. 

For greater detail, and for impact studies, higher resolution regional models can be 

‘embedded’. This means that a regional model, which represents a limited area of the globe 

at higher resolution, takes all information for the surrounding area from a global climate 

model. The version of the Hadley Centre regional model used to produce the UKCIP02 

scenarios, HadRM3, has a horizontal resolution of 50km. The regional model prediction 

shows much more detail than the global model and is able to better represent extremes. 

Regional models are able to better capture extreme weather because not only can they 

represent smaller scale weather features but they also have a much better representation of 

orography. For example, the mountains of Scotland cannot be represented in the global 

model at all; the entire country is represented by two grid boxes. In the UKCIP02 scenarios, 

the 50km regional climate model (RCM) permits the mountains of Scotland to be partially 

resolved which results in increased spatial variation of rainfall. The model used for the British 

Irish Council report (Jenkins et al, 2003) was a single run of a 25 km RCM, the finer 

resolution resulting in an ability to represent the varied topography of Scotland more 

accurately. The increased resolution also permitted some of the Scottish islands to be 

resolved, and included in climate modelling studies, for the first time. 

Every climate model, global or regional, produces a wealth of data. To achieve maximum 

value this data must be used in the context of the uncertainties (to be discussed later in the 

technical handbook), and it must also be remembered that not all climate model data have 

been validated against observed climate. The observational datasets listed in this study can 

all be used to validate the performance of models. 

All modelled data from the global model, HadCM3, are available from present day to 2100 

(and beyond in some cases) under a number of emissions scenarios, however as Scotland is 

represented by two grid boxes in the global model this is likely to be of limited practical use in 

studies of Scottish climate. The RCM (both 50km and 25km) has been run for two thirty year 

periods, a present day time-slice (1961 to 1990) and a future time-slice (2071 to 2100). 

These represent the current and projected future climates. Daily data are available 

throughout both of these periods. Many physical parameters are available, such as 

precipitation, snowfall, humidity, temperature, etc, with a representative list being given in 

Table A.1 of the UKCIP02 report (Hulme et al, 2002). Although this list is for monthly mean 

data, and is by no means exhaustive, it is indicative of the parameters available from the 

Hadley Centre model integrations. 

Aggregation of data to larger geographical areas will diminish the impact of extreme events. 

However, understanding the regional impact of climate change can be usefully achieved by 

assigning sub-regions which exhibit similar impacts. In the case of Scotland it may be useful 

to consider three such sub-regions. Taking average changes over the mountainous west 

coast, south-eastern Scotland, and northern Scotland may prove a valuable descriptor of 

changes such as summertime precipitation under different emissions scenarios. Such 

regions, defined by their climatological characteristics, are used in the Met Office’s datasets 

(listed in Appendix 1). Other definitions of regions exists, such as the four Scottish regions 

68


(Appendices) 

defined by Gregory et al (1991) however, for consistency with the available data, this project 

will be restricted to the Met Office’s three. 

The full range of marker scenarios must also be considered, where possible, as each is 

considered to be of equal likelihood. Consideration of all of the marker scenarios provides a 

useful guide as to the range of plausible possible futures as climate changes. 

69


(Appendices) 

6. RECOMMENDATIONS 

The selection of variables for inclusion in the handbook is dependent upon a number of 

factors. The selection will be based upon 

• Realised and future changes 

• Data availability – past, present and future 

• Applicability to a broad audience 

• Ease of calculation 

• Budgetary and time constraints 

The selection of variables also needs to take cognisance of the sample size of Scottish 

representatives surveyed and the industry biases that they may have. While the survey 

should be used as a guide it should not dictate the content of the handbook. For example, 

the eagerness to see the compilation of rainfall returns periods may be impractical owing to 

computational demand, budgetary constraints and their suitability for representing climatic 

change. It must also be recognised that the analysis of realised changes is limited by data 

availability. The same could, of course, be said of the variables in future datasets. 

70


(Appendices) 

7. REFERENCES 

IPCC (2001) Climate Change 2001: The Scientific Basis. Contribution of Working Group I to 

the Third Assessment Report of the Intergovernmental Panel on Climate Change. 

[J.T.Houghton, J.T., Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell 

and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and new 

York, NY, USA, 881pp. 

Gregory, J. M., P. D. Jones and T. M. L. Wigley (1991) Precipitation in Britain: an analysis of 

area-average data updated to 1989. Int. J. Climatol., v.11, n.3 pp.331-345 

Hulme, M., G.J. Jenkins, X. Lu, J.R. Turnpenny, T.D. Mitchell, R.G. Jones, J. Lowe, J.M. 

Murphy, D. Hassell, P. Boorman, R. McDonald and S. Hill (2002) Climate Change Scenarios 

for the United Kingdom: The UKCIP02 Scientific Report. Published by the Tyndall Centre, 

UEA Norwich, April 2002. 

Jenkins, G.J., C Cooper, D Hassell and R Jones (2003) Scenarios of climate change for 

islands within the BIC region. Published by the Met Office, Bracknell, July 2003. 

NERC (1975) Flood Studies Report, Institute of Hydrology, Wallingford, Oxford 

Stott, P.A.(2003) Attribution of regional-scale temperature changes to anthropogenic and 

natural causes, Geophys. Res. Lett., v. 30, n.14, p.1728 

71


(Appendices) 

Appendix 1, Annex 1 : Datasets of observed current climate. 

See source websites for full details of each dataset, licensing, etc 

Point datasets 

Table A1.1 

Table A1.2 

Table A1.3 

Table A1.4 

Temperature 

Rainfall 

Sunshine 

Marine 

Gridded data 

Table A1.5 

Table A1.6 

Table A1.7 

Table A1.8 

Table A1.9 

Table A1.10 

Table A1.11 

Temperature 

Rainfall 

Snow 

Sunshine 

Marine 

Other elements 

Other datasets 

Key 

M = monthly average 

S = seasonal average 

A = annual average 

V = various recording periods 

* stored as an image 

** dependent upon licensing conditions. 

72

SNIFFER Project CC03: Patterns of climate change across Scotland (appendices) April 2006 

Table A1.1 Temperature 

Dataset 

Start End Mean Location Source Web address Licence? Cost? 

Date Date period 

Maximum temperature 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Maximum temperature 1873 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Airport 

Maximum temperature 1931 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Maximum temperature 1959 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Maximum temperature 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Maximum temperature 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Minimum temperature 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Minimum temperature 1873 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Airport 

Minimum temperature 1931 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Minimum temperature 1959 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Minimum temperature 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Minimum temperature 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Grass minimum temp 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Grass minimum temp 1942 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Airport 

Grass minimum temp 1931 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Grass minimum temp 1959 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Grass minimum temp 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

73


Maximum temperature 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Maximum temperature 1961 1990 30-year 

(M/A) 

mean minimum 

1961 1990 30-year 

temperature 

(M/A) 

days of air frost 1961 1990 30-year 

(M/A) 

mean maximum 

1971 2000 30-year 

temperature 

(M/A) 

mean minimum 

1971 2000 30-year 

temperature 

(M/A) 

days of air frost 1971 2000 30-year 

(M/A) 

Various 

(16 stations) 

Various 

(16 stations) 

Various 

(16 stations) 

Various 

(16 stations) 

Various 

(16 stations) 

Various 

(16 stations) 

Met Office http://www.metoffice.gov.uk/climate/uk/averages/19611990/index.html No No 






74


Table A1.2 Rainfall 

Dataset 



Total rainfall 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total rainfall 1873 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Airport 

Total rainfall 1931 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total rainfall 1961 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total rainfall 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total rainfall 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total rainfall 1961 1990 30-year 

(M/A) 

Days of rain >1mm 1961 1990 30-year 

(M/A) 

Total rainfall 1971 2000 30-year 

(M/A) 

Days of rain >1mm 1971 2000 30-year 

(M/A) 

Various 

(16 stations) 

Various 

(16 stations) 

Various 

(16 stations) 

Various 

(16 stations) 





75


Table A1.3 Sunshine 

Dataset 



Total sunshine duration 1930 2004 M Lerwick Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total sunshine duration 1929 2004 M Stornoway Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Airport 

Total sunshine duration 1928 2004 M Tiree Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total sunshine duration 1961 2004 M Braemar Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total sunshine duration 1957 2004 M Leuchars Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total sunshine duration 1959 2004 M Paisley Met Office http://www.metoffice.gov.uk/climate/uk/stationdata/index.html No No 

Total sunshine duration 1961 1990 30-year 

(M/A) 

Total sunshine duration 1971 2000 30-year 

(M/A) 

Various 

(16 stations) 

Various 

(16 stations) 



76


Table A1.4 Marine 

Dataset 



Sea surface temperature 1949 2004 D Keppel Pier, BODC http://www.bodc.ac.uk Yes Yes 

Clyde 

Moored current meters 16 1968 - - various CEFAS http://www.cefas.co.uk 

North Sea Groundfish survey 1982 1991 A North Sea 

(various) 

Western European Shelf 1982 - A W. European 

Groundfish survey 

Shelf 

CEFAS http://www.cefas.co.uk 

CEFAS http://www.cefas.co.uk 

MLA moored self-recording 1967 - V Various FRS, Marine Lab., 

instrument data 17 Aberdeen 

www.bodc.ac.uk/services/current_meter_search/ 

current_meter_search.html 

Yes 

Yes 

MLA hydrographic data 18 1893 - V Various FRS, Marine Lab, 

Aberdeen 

MLA Thermosalinograph 1970 - V Various FRS, Marine Lab., 

Data 19 Aberdeen 

http://www.ices.co.uk No 

http://www.ices.co.uk No 

UK National Databank of 

Coastal Tide gauge data 

1842 - V Scottish coasts BODC http://www.bodc.ac.uk Yes Yes 


Moored Current Meter Data 

1967 - V NE Atlantic and 

continental shelf 

BODC http://www.bodc.ac.uk Yes Yes 

UK National Databank of 1975 - V NE Atlantic and 

CTD/STD profiles 20 continental shelf 

BODC http://www.bodc.ac.uk Yes Yes 

UK classical hydrographic 1893 - V UK Shelf seas BODC or ICES http://www.bodc.ac.uk or http:// www.ices.dk/ocean Yes Yes 

station data set 21 

16 Current speed and direction, also temperatures, pressure and conductivity recorded 

17 Dataset updated annually. Ocean currents, ocean temperature, ocean circulation, current speed and direction, temperature, conductivity (salinity), pressure. 

18 Dataset updated annually. Pressure, temperature, salinity, oxygen, phosphate, nitrate, silicate, ammonia, chlorophyll-a, phaeopigments, particulate organic carbon 

and particulate organic nitrogen. 

19 Updated 6-8 times a year. Temperature, salinity, fluorescence and occasionally soundings logged with data, time and position (as latitude and longitude). 

20 Conductivity/salinity, temperature, depth/pressure, occasionally oxygen, transmittance, chlorophyll fluorescence 

21 Temperature, salinity, nutrients, oxygen, pH, alkalinity, and chlorophyll-a. 

77



Wave Data 

1955 1985 V Various BODC http://www.bodc.ac.uk Yes Yes 

UK World Ocean Circulation 1991 - V North Atlantic BODC http://www.bodc.ac.uk Yes Yes 

set 22 

Experiment (WOCE) data 

Mean Sea Level 1933 - M/A Various 23 Permanent Service 

for mean Sea Level 

http://www.pol.ac.uk/psmsl No No 

22 Temperature, salinity, dissolved oxygen, nutrients, tracers, carbonic system, bathymetry, surface meteorology, current profiles 

23 Scottish locations included Lerwick, Sullom Voe, Wick, Invergordon, Moray Firth, Buckie, Aberdeen, Dundee, Rosyth, Leith, Dunbar 

78


Table A1.5 Temperature 

Dataset 

Start End Mean Spatial Source Web address Licence? Cost? 

Date Date period scale 

Maximum temperature * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Minimum temperature * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Mean temperature * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

30cm soil temperature * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Grass minimum 

1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

temperature * 

(m/s/a) 

Office 

Days of ground frost * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Days of air frost * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Maximum temperature * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Minimum temperature * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Mean temperature * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

30cm soil temperature * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Grass minimum 

1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

temperature * 

(m/s/a) 

Office 

Days of ground frost * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Days of air frost * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Maximum temperature 1914 2000 M 5km Met 

Office 

www.metoffice.gov.uk/research/hadleycentre/obsdata/ukcip/index.html Yes Yes/ 

No** 

Minimum temperature 1914 2000 M 5km Met 

Office 


No** 

79


Mean temperature 1914 2000 M 5km Met 

Office 

No. of days of air frost 1961 2000 M 5km Met 

Office 

No of days of ground 1961 2000 M 5km Met 

frost 

Office 

Annual extreme 

1961 2000 A 5km Met 

temperature range 

Office 

Heating degree days 1961 2000 A 5km Met 

Office 

Growing degree days 1961 2000 A 5km Met 

Office 

Growing season length 1961 2000 A 5km Met 

Office 

Summer heat wave 1961 2000 A 5km Met 

duration 

Office 

Winter heat wave 

1961 2000 A 5km Met 

duration 

Office 

Summer cold wave 1961 2000 A 5km Met 

duration 

Office 

Winter cold wave 

1961 2000 A 5km Met 

duration 

Office 

Mean temperature area 1914 2000 M Scotland Met 

series 

Office 

Highest maximum 1961 1990 Jan/Jul 5km Met 

temperature * 

Office 

Lowest maximum 

1961 1990 Jan/Jul 5km Met 

temperature * 

Office 

Highest minimum 


temperature * 

Office 

Lowest minimum 


temperature * 

Office 


No** 


No** 


No** 


No** 


No** 


No** 


No** 


No** 


No** 


No** 


No** 

http://www.metoffice.gov.uk/climate/uk/seriesstatistics/scottemp.txt No No 

http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 




80


Table A1.6 Rainfall 

Dataset 



Total Precipitation * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Days of rain > 0.2mm * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Days of rain > 1mm * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Total Precipitation * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Days of rain > 0.2mm * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Days of rain > 1mm * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Days of rain > 1mm 1961 2000 M 5km Met 

Office 


No** 

Days of heavy rain 

>10mm 

1961 2000 M 5km Met 

Office 


No** 

Total precipitation 1914 2000 M 5km Met 

Office 


No** 

Max no of consecutive 

dry days 

1961 2000 A 5km Met 

Office 


No** 

Greatest 5-day 

precipitation total 

1961 2000 A 5km Met 

Office 


No** 

Rainfall intensity 1961 2000 A 5km Met 

Office 


No** 

Precipitation area 1914 2000 M Scotland Met http://www.metoffice.gov.uk/climate/uk/seriesstatistics/scottemp.txt No No 

series 

Office 

Days of heavy rain > 

10mm* 

1961 1990 Jan/Jul/ 

A 

5km Met 

Office 


81


Table A1.7 Snow 

Dataset 



Days of snow cover 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

>50% * 

(m/s/a) 

Office 

Days of snow lying * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

No of days with snow 

falling 

1961 2000 M 5km Met 

Office 


No** 

No of days with snow 

cover 

1961 2000 M 5km Met 

Office 


No** 

Days of heavy rain > 

10mm* 

1961 1990 Dec/Jan/ 

Feb/S 

5km Met 

Office 


Table A1.8 Sunshine 

Dataset 



Sunshine hours * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Sunshine hours * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Cloud cover 1961 2000 M 5km Met 

Office 


No** 

Mean hours of bright 

sunshine 

1929 2000 M 5km Met 

Office 


No** 

Sunshine hours areal 

series 

1929 2000 M Scotland Met 

Office 

http://www.metoffice.gov.uk/climate/uk/seriesstatistics/scotsun.txt No No 

Table A1.9 Marine 

Dataset 

HadISST1, sea ice and 

sea surface temperature 

Start 

Date 

End 

Date 

Mean 

period 

Location Source Web address Licence? Cost? 

1870 2004 M 1 degree Met Office http://www.metoffice.gov.uk Yes Yes/ 

No** 

82


Table A1.10 Other elements 

Dataset 



Days of thunder * 1961 1990 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

(m/s/a) 

Office 

Days of thunder * 1971 2000 30-year 1km Met http://www.metoffice.gov.uk/climate/uk/averages/19712000/mapped.html No No 

(m/s/a) 

Office 

Mean sea level 

pressure 

1961 2000 M 5km Met 

Office 


No** 

Vapour pressure 1961 2000 M 5km Met 

Office 


No** 

Mean wind speed 1969 2000 M 5km Met 

Office 


No** 

Maximum relative 1961 1990 Jan/Jul 5km Met www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

humidity * 

Office 

Minimum relative 1961 1990 Jan/Jul 5km Met www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

humidity * 

Office 

Windspeed at 10m * 1961 1990 Jan/Jul/ 5km Met www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

A 

Office 

Days of hail * 1961 1990 S/A 5km Met 

Office 

www.metoffice.gov.uk/climate/uk/averages/19611990/mapped.html No No 

Table A1.11 Other data sources 

Dataset Web address Description 

Integrated Coastal Hydrography 

Project 

http://www.coastalhydrography.com 

Integrated Coastal Hydrography (ICH) is a practical partnership between the United 

Kingdom Hydrographic Office (UKHO), the Environment Agency, Ordnance Survey and 

the Maritime and Coastguard Agency (MCA). It aims to produce an on-line database of 

hydrographic metadata 

Summary of the climate of 

Scotland, including extremes 

http://www.metoffice.gov.uk/climate/uk/location/ 

scotland/index.html 

Bathing water data 

http://www.sepa.org.uk/data/bathingwaters/bw2005/ SEPA's Annual Bathing Water reports and regularly-updated monitoring results for 

Harmonised monitoring data 

(water quality) 

index.htm 

http://www.sepa.org.uk/data/hm/index.htm 

identified and non-identified waters around the coast of Scotland. 1988 to present. 

The Harmonised Monitoring Scheme for river water quality commenced in 1974. The 

Harmonised Monitoring Scheme is a national archive of water quality data aimed at 

83


The National Groundwater Level 

Archive 

National Marine Monitoring 

Programme (NMMP) 

http://www.nwl.ac.uk/ih/nrfa/groundwater/index.htm 

http://www.cefas.co.uk/monitoring/page-b3.htm 

providing information throughout the United Kingdom, including the estimation of river 

borne input of selected contaminants to the sea. The sampling network including 230 

sites, mainly located on major rivers at, or near, the tidal limit. In Scotland there are 58 

sites. 

The National Groundwater Level Archive (NGLA) is maintained by the British Geological 

Survey at Wallingford and holds water level data for around 170 wells and boreholes 

throughout the United Kingdom 

The National Monitoring Plan (now called the National Marine Monitoring Programme) 

was initiated in the late 1980s to co-ordinate marine monitoring in the United Kingdom 

between a number of organisations. The NMMP aims to detect long-term trends in the 

quality of the marine environment, to ensure consistent standards in monitoring, to 

establish appropriate protective regulatory measures, to co-ordinate and optimise 

marine monitoring in the UK, and to provide a high quality key dataset for key variables. 

The Department for Environment, Food and Rural Affairs, is a major funder of the 

NMMP. 

National River Flow archive http://www.nwl.ac.uk/ih/nrfa/index.htm To service a very broadly-based need for river flow data the UK maintains a network of 

over 1300 gauging stations. Responsibility for these stations in Scotland rests 

principally with the Scottish Environment Protection Agency. Data from the UK based 

measuring authorities now constitute a database of around 50,000 station years of daily 

and monthly flow data. In addition, monthly catchment rainfall data (mostly derived from 

data provided by The Met Office) are routinely archived. 

UK atmospheric deposition data 

ITE Edinburgh; Contact: Prof. D. Fowler / Mr. R.I. 

Smith; df@ite.ac.uk; 

Spatial estimates of pollutant wet and dry deposition, including NO3-, NH4+, NO2, NH3, 

O3, total N deposition. Estimates available on a grid scale basis and for different 

receptor ecosystems within each grid square. Available for 1992 - present for 20km grid 

squares. 

84

SNIFFER Project CC03: Patterns of climate change across Scotland April 2006 

(Appendices) 

Appendix 1, Annex 2: Stakeholder organisations surveyed 

Table A.2.1 Stakeholder organisations contacted 

ORGANISATION 

Scottish Exec 

Forestry Commission 

SEPA 

Rail track Scotland 

SCOTS (Society of Chief Officers for Transportation in 

Scotland) 

Visit Scotland 

Scottish and Southern Electric 

Scottish Power 

Scottish Water 

Scottish Enterprise 

NFU Scotland 

SAC 

RSPB Scotland 

COSLA (Convention of Scottish Local Authorities) 

Highland council 

Dundee City Council 

Edinburgh City Council 

Perth and Kinross C. 

Stirling C 

Aberdeen C 

Sustainable Scotland Network 

RESPONSE 

RECEIVED? 

Y 

Y 

Y 

Y 

N 

N 

N 

Y 

Y 

N 

Y 

N 

Y 

Y 

N 

Y 

N 

N 

Y 

N 

N 

85


(Appendices) 

86


(Appendices) 

APPENDIX 2: A BRIEF DISCUSSION OF UNCERTAINTY IN CLIMATE MODELLING 

87


(Appendices) 

A BRIEF DISCUSSION OF UNCERTAINTY IN CLIMATE MODELLING 

There are three key areas of uncertainty in climate modelling. These relate to emissions 

scenarios, scientific uncertainties and the impact of natural variability. 

i.) 

Emissions scenarios 

Future anthropogenic emissions of gases that alter climate will depend upon the way in which 

society evolves. There is no way of knowing how population, technology, economic growth, etc., 

will develop and thus ‘scenarios’ of future development have to be constructed. The IPCC 

Special Report on Emission Scenarios (SRES, IPCC, 2000) considered four plausible narrative 

storylines and from these, produced details of a wide range of possible future emissions 

scenarios, where each scenario associated with a particular storyline is considered a member of 

that ‘family’. This is illustrated in Figure A1 that shows the CO 2 emissions associated with the 

‘marker scenario’ for each family, where marker scenarios are considered representative of a 

storyline. 

It is this set of marker scenario which were used in the UKCIP02 report (A1FI, A2, B2 and B1) 

although they were relabelled as ‘high’, ‘medium-high’, ‘medium-low’, and ‘low’ respectively. As 

a rough guide, the ’medium-high’ emissions scenario can be considered to approximate to a 

‘business as usual’ evolution. It must be noted however that no likelihood of occurrence can be 

placed upon any of the storylines of emissions scenarios. Although the scenarios diverge very 

quickly, all are plausible and while they may not be equally probable they are possible, therefore 

none can be discounted. This is why predictions should always be qualified by saying which 

scenario of forcing was used when the result was produced. 

As predicted climate changes depend upon the scenario of forcing used it is not surprising that 

a range of possible futures results. When considering the global mean temperature change 

predicted by a single global model the choice of forcing scenario actually has very little impact 

over the next fifty years (not shown). It is only in the second half of this century that predictions 

begin to diverge. This is because of the large thermal inertia of the climate system and the long 

lifetime of CO 2 . This means that the changes global climate will experience over the next few 

decades are already programmed into the climate system because of the emissions of recent 

decades. 

Figure A1. Emissions of carbon dioxide in four of the SRES emissions scenarios. (Source, 

Hadley Centre Technical Note 44) 

88


(Appendices) 

ii.) 

Scientific uncertainties 

The IPCC Third Assessment Report (IPCC TAR, 2001) included predictions from over thirty 

models of varying complexity. Each model was run using the same SRES scenarios but each 

model predicts a different future, and some of the differences are large, much greater than the 

range introduced by the choice of emissions scenario. These differences are due to the way the 

models each represent the globe, the processes that are included and the manner in which they 

are parameterised. Some models have a finer resolution than others and include more complex 

physical processes. It was not possible, at this time, to say how credible each model was 

because evaluation is not simple and until recently included some level of subjectivity. It was 

therefore not possible to discount any of the models. Even the more extreme predictions could 

be underestimating what will occur because a vital feedback process could be as yet 

undiscovered and therefore is not represented in the models. 

The range of futures predicted by the different models is one of the largest uncertainties in 

prediction of climate change, however when model predictions are consistent, increased 

confidence can be placed in the result. For example, all models predict global warming under all 

scenarios of forcing. Difficulties arise when there is a low level of consistency between model 

results. Figure 26 of the UKCIP02 report (not shown) illustrates this, comparing changes in 

winter precipitation over the UK as predicted by nine different global climate models. The 

models presented in the figure all predict an increase in winter precipitation over Scotland but 

the range of predicted change is quite large, from just greater than zero to over fifty percent. 

Given the nature of weather patterns across the UK it is perhaps unsurprising that it is a 

challenging area to model, a slight shift in the location of a pressure system over the Atlantic 

can mean that storms may track to the north or south rather than travelling across Scotland. 

Work is continually being done to validate the representation of current climate by the models 

and to find plausible reasons for the different climate predictions of models. 

The impact of scientific uncertainties can be easily demonstrated by comparing the results of 

the UKCIP98 report, the 2001 report by Hulme et al and the UKCIP02 report. Each of these 

publications was based upon Hadley Centre modelling results but in each case a different 

model was used. UKCIP98 was based upon the Hadley Centre’s HadCM2 global model. Winter 

precipitation was predicted to increase over Scotland and indeed the increase was seen to 

persist throughout the year with the summer months also experiencing more rainfall under most 

of the emissions scenarios by the 2080s. It must be noted however that these results came from 

a global climate model in which Scotland was represented by only two model grid points. 

The UKCIP98 report was followed in 2001 by ‘An exploration of regional climate scenarios for 

Scotland’ (Hulme et al 2001) presenting results from HadRM2, the Hadley Centre’s regional 

version of the model used in UKCIP98. Although this model was scientifically the same as the 

model used in UKCIP98 it had a much greater horizontal resolution of fifty kilometres, so spatial 

detail of the predicted climate changes over Scotland became possible. In this case only one 

scenario of emissions forcing (Medium-High, 2080s) was available so a normalising technique 

was employed to allow the regional model predictions to be compared more easily with those 

from the global model. It must be remembered that values presented in this report are 

normalised and so represent the changes that may be expected over Scotland for each degree 

Celsius increase in global mean temperature. Hence, the size of a predicted change is not 

directly comparable with either UKCIP98 or the later UKCIP02. 

It was found that results were broadly similar to those found in the UKCIP98 report although the 

spatial resolution permitted identification of an east-west contrast in precipitation changes. In 

particular, the greatest predicted increase in precipitation occurs over the Western Highlands 

with increased precipitation throughout the year. However the model also predicted decreased 

rainfall over eastern Scotland during summer months, a result not seen in the UKCIP98 report. 

The study also found relatively little difference in the predicted change to precipitation return 

89


(Appendices) 

periods between the regional and global models, although the intensity of rainfall is greater in 

HadRM2. 

The results contained within the UKCIP02 report came from the Hadley Centre’s latest regional 

climate model, HadRM3, based upon the global model HadCM3, the successor to the model 

used in UKCIP98. Although HadCM3 is scientifically more complex than its predecessor, it 

cannot be argued that it is scientifically more valid than HadCM2. The models include different 

parameterisations and thus predict slightly different regional patterns of climate change. This is 

to be expected. The reports also use slightly different periods (2081 to 2100 in HadRM2 versus 

2071 to 2100 in HadRM3) and different emissions scenarios. All of the differences are 

discussed in Section 7.5 of the UKCIP02 report but the major difference is in summertime 

rainfall across Scotland with the latest model predicting a widespread drying when HadRM2 

predicted generally wetter summers. While some of the differences can be explained by natural 

variability the major contributing factor is the different large scale circulation patterns established 

in each model. While many general features of the simulated climate are similar between the 

models, each predicted climate is modulated (locally and seasonally) by changing patterns of 

large scale air flow. 

iii.) 

Natural variability 

The Earth’s climate varies naturally, with the climate system’s internal variability providing year 

to year and decade to decade change. It is highly likely that at some time in the future there will 

be periods when this natural variability combines with anthropogenic climate change to produce 

a period of extreme warming or summer drying while it is equally likely that the two will combine 

at another time to produce a relatively cold or dry winter. For this reason is it important to 

consider natural variability when looking at predicted mean climate change. 

One technique to address the uncertainty due to natural variability as simulated within climate 

models is to run an ensemble of integrations. The starting conditions of a model can be 

‘perturbed’ slightly which sets a model off on a slightly different, but equally plausible, predictive 

pathway. This technique effectively introduces new ‘weather’ to the starting conditions, 

introducing a small but feasible alteration of starting conditions. The difference which results 

from predictions by members of such an ensemble, in which each member has identical 

physics, is the modelled representation of natural variability. 

The majority of mapped results presented in the UKCIP02 report are for an ensemble mean. 

Three integrations with slightly perturbed starting conditions where completed for the control 

period (1961 to 1990) and for the 2080s time-slice with the Medium-High emissions scenario. 

This means that three sets of thirty year integrations are available for each period. In this way 

the simulated variability of the modelled present day climate can be more fully assessed and the 

impact of climate change on variability more fully captured than could be achieved with a single 

ensemble member. 

90


(Appendices) 

APPENDIX 3: GLOSSARY 

91


(Appendices) 

GLOSSARY 

5DR maximum five-day precipitation amount 

CDD consecutive dry days (also used in other text to refer to cooling degree-days) 

CWD(s/w) cold-wave duration (summer/winter half-year). Cold Wave duration = ∑ days with 

1961-1990 daily normal - daily T_min > 3 °C for ≥ 6 consecutive days 

DTR diurnal (or daily) temperature range 

ENSO El Niño Southern Oscillation 

ETR extreme temperature range 

GCM global climate model or general circulation model 

GDD growing degree days. Growing Degree Days = ∑ daily T_mean – 5 for T_mean > 

5 °C. 

GIS Geographical information system 

GMT Greenwich mean time 

GSL growing season length. Growing season length = period (days) bounded by daily 

T_mean > 5 °C and < 5 °C (after 1st July) for ≥ 6 days 

HadCM3 A global climate model developed by the Hadley Centre at the Met Office 

HDD heating degree days. Heating Degree Days = ∑ 15.5 – daily T_mean for T_mean 

< 15.5 °C 

hPa hectopascal, a unit of pressure equivalent to a millibar 

HWD(s/w) heat-wave duration (summer/winter half-year). Heat Wave duration = ∑ days with 

daily T_max – 1961-1990 daily normal > 3 °C for ≥ 6 consecutive days. 

IPCC Intergovernmental Panel on Climate Change 

NAO North Atlantic Oscillation 

NAO index A measure of the pressure gradient between the Icelandic low and Azores high 

pressure systems. The index indicates the phase of the NAO. 

RCM regional climate model 

RI 

rainfall intensity 

SRES Special report on emissions scenarios 

UKCIP United Kingdom climate impacts programme 

UKCIP02 Scenarios created in 2002 as part of UKCIP output, using HadRM3, a Hadley 

regional climate model 

UKCIP98 Scenarios created in 1998 as part of UKCIP output, using HadCM2, a global 

climate model 

WMO World Meteorological Organisation 

92

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