DelegatePack_DroughtConference_20-21March2019

Speakers
Day 1: Plenary – The Pichette Auditorium continued
Massimiliano Pasqui CNR (Italian National Research Council)
A customizable drought monitoring and seasonal forecasting service to support different users’
needs
Massimiliano Pasqui is a climate scientist whose main interests are numerical modelling in support of weather
forecasts, climate data analysis, seasonal forecast predictability and climate change impacts. He participates in a
number of national and international projects in these fields. He is the author of numerous scientific papers on
international journals/books on atmospheric science and climate change mechanisms and impacts in the
Mediterranean basin and Africa. In the last decade he has been engaged as a contract professor in meteorology,
numerical modelling and climatology courses at several Italian universities.
Bramha Dutt Vishwakarma University of Bristol
Novel metric for water stress from the Gravity Recovery & Climate Experiment (GRACE) satellite
mission
The GRACE satellite mission recorded time-variability in Earth’s gravity for more than a decade, which can be directly
related to changes in water stored near the surface of the Earth. GRACE maps of water mass change are available at
monthly time scale and have been used to validate hydrology models, close regional water budgets, estimate
groundwater changes and map water stress. Usually the GRACE time series is decomposed into a linear trend and a
periodic signal and then the magnitude of the trend is used to infer the severity of water mass in a region. In this
study we show that such an approach is misleading because catchment scale hydrology also contains inter-annual
signals with decadal frequencies that are also recorded by GRACE. Since the quality-controlled GRACE record is only
about 13 years long, the long wavelength inter-annual signal cannot be co-estimated and will contaminate estimates of
linear trend. Furthermore, the inter-annual behaviour of each catchment is different and, therefore, a catchment
should not be evaluated against other catchments but with respect to its natural variability. Therefore, to quantify
water-stress comprehensively, we propose a novel metric for water stress that uses GRACE trend and inter-annual
variability from a calibrated 62-years-long hydrology model time series. We obtain a global water stress map that
differs markedly from previous GRACE assessments. We find that more than 1.5 billion people in 39 river catchments
are facing severe water stress and this number will rise by 50% in 2025 if current trends continue.
Day 1: Parallel Session 1 Climatology and Hydrology – Pichette Auditorium
Jamie Hannaford presenting for Katie Smith CEH
Reconstructing historic flow data to inform management
Hydrological models can provide estimates of streamflow pre- and post- observations, which enable greater
understanding of past hydrological behaviour and potential futures. We outline a new multi-objective calibration
method which was derived and tested for 303 catchments in the UK. The calibrations were used to reconstruct river
flows back to 1891 to provide a much longer view of past hydrological variability given the brevity of most UK river
flow records which commenced post-1960. This work provides an exemplar framework for calibrating catchment
models for use in multiple applications. The ~125 year spatially and temporally consistent reconstructed flow dataset
derived for this study will also allow comprehensive quantitative assessments of past UK drought events, as well as
long-term analyses of hydrological variability that have not been previously possible. This will allow water resource
managers to better plan for extreme events, and build more resilient systems for the future.
Lucy Barker CEH
How severe were historic hydrological droughts in the UK? Insights from a systematic
characterisation and ranking of events back to 1891
The relative shortness of river flow records in the UK means that it is not possible to characterise hydrological
droughts prior to the 1960s in many places across the country. We know from individual long river flow records,
regional flow reconstructions and qualitative data that severe hydrological droughts occurred in the late 19th and
early 20th Century; but until recently it hasn’t been possible to identify and characterise these droughts across the
UK. New daily river flow reconstructions for 303 catchments across the UK, dating back to 1891 have enabled
national scale, drought identification and characterisation. For 108 near-natural catchments across the UK, using the
Standardised Streamflow Index for accumulation periods of 3 and 12 months, hydrological drought events over
~125 years from 1891 to 2015 have been systematically identified, characterised and ranked. Extracted events were
ranked according to four characteristics: duration, accumulated deficit, mean deficit and maximum intensity in order
to assess how the events compare when different aspects of severity were considered. These results provide an
unprecedented view of drought severity in the UK, shedding light on those events outside of the observed period
(e.g. the early 1920s) and that are poorly documented in qualitative sources (for example the droughts of the 1940s).
This extended understanding of past droughts is crucial to inform the planning and management of future events,
aiding the development of scenarios outside the range of those seen in observed data and providing benchmarks
against which to compare current and future events.