ClimateChange Assessment Guide.pdf - University of Waterloo

Climate Change Assessment83• Select Assessment AR4 (2007).• Choose one of CGCM3T47-RunX, CGCM3T63 orHadCM3.• Select Experiment. The experiments available indaily format are A2 for CGCM3, and A2 and B2 forHadCM3; therefore select one of these scenarios.• Select variables air temperature, precipitation total,surface down-welling shortwave radiation (i.e., solarradiation) and wind speed (10 m).• Select time period as either 1961 to 1990 or 1971 to2000 for existing conditions and 2020s, 2050s or 2080sfor future conditions.• Click Get Data. You will receive files with annual,seasonal and monthly mean and annual standarddeviation by parameter and time period.To acquire the daily time step climate data follow thepath to the DAI Welcome and sign in site.• Select Global Models on the left side of the screen.• Select CGCM3.1 or HadCM3.• Click on Browse Available Data.• Select Variables.• Select Domain.• Select Experiment.• Indicate desired Format (i.e., text) and Frequencies(i.e., daily).The available datasets include the A2 scenario for theCGCM3 and the A2 and B2 scenarios for the HadCM3.Data will be provided as monthly text files with dailydata for each parameter and time period. Data must bereorganized and reformatted in columns.LARS-WG has four major stages in the process ofgenerating future climates: Site Analysis, Q-test,Generator and Creating GCM climate scenarios.These are summarized below. Refer to the downloadablemodel manual for a detailed description of the processwith examples.The Site Analysis step examines the baseline climatetime series data for errors and determines statisticalcharacteristics for the data. Frequency distributions aredetermined for the observed data for wet and dry seriesdurations and precipitation amounts and solar radiationamounts. A Fourier series is used to characterizemaximum and minimum daily temperatures.The model Generator routine uses the informationcollected in the site analysis step to build a file withobserved data characteristics. This file is then used bythe model to generate synthetic data time series withstatistical characteristics that are nearly identical to thebaseline case. One use of this is to extend observeddata time series.Qtest is a model utility that provides a statisticalcomparison between observed data and generatedclimate data. A variety of tests and comparisons areprovided. Several of these are helpful in a generalcomparison between future and baseline climates,discussed later in this section.The observed data characteristic file is altered toaccount for future climate characteristics. Generatoris then run with the altered characteristics to generatedaily output for the weather variables. The future climatecharacteristics of interest are the monthly changes inmean values, the changes in wet and dry period durationand changes in standard deviations of daily precipitationamounts, temperatures and solar radiation. If standarddeviations (i.e., variability) are left unchanged from thebaseline case then LARS-WG will generate a climate thatis statistically similar to that generated by the changefield method.Methods for Creating GCM climates, includingvariability in future climates, are discussed in the manual.These are based upon analyzing the variability (i.e.,standard deviations) in the daily GCM output for thesame weather variables and the future time horizons ofinterest.It may be found that the future daily GCM precipitationdata contains many days with very small amounts ofrain and very few dry days. This unrealistic conditionprecludes using this data for determining futurevariability and applying the weather generator foranalysis of variability, as this method relies uponthe distribution of wet and dry days as the basis forgenerating precipitation events. Unfortunately, thecondition leading to many days with small amounts ofprecipitation is relatively common in daily GCM output.The weather generator can be run to generate futureclimates without the adjustments to future variability, butthese runs will generate climates that are very similar tothose generated using the change field method for thesame GCM and emission scenario.