ClimateChange Assessment Guide.pdf - University of Waterloo

Guide for Assessment of Hydrologic Effects of Climate Change in Ontario82The model will determine multiple linear regressionrelationships for each predictand based upon thepredictors selected, temporal resolution (i.e., annual,seasonal or monthly) and the time period of the data.Goodness of fit parameters are provided so that theuser can decide whether the model is of sufficientquality to proceed. This stage may be repeated totest the value of data transformations and alternativepredictor choices.5. Weather generator. This stage allows the user togenerate synthetic predictor time series representingexisting conditions using the relationships establishedin the calibration stage. The synthesized data canbe used both to validate the model by comparing itwith observed data and to generate an ensemble ofcurrent condition time series for use in assessments.6. Statistical analysis of data. This facility allows the userto determine a large number of statistical metrics (i.e.,mean, % of wet days, peaks above thresholds, etc.) forthe observed and synthesized data. This informationcan be used to compare the two datasets and providefurther validation of their similarity. Graphics are alsoavailable to facilitate comparisons.7. Scenario generation. This final stage synthesizesfuture predictand time series based upon thedownloaded scenario predictor time series and thesame statistical relationships used in the weathergenerator stage.It is possible to create SDSM based future predictandfiles representing four GCM-scenario combinationsfor use in hydrologic assessments. These include theHadCM3 with A2 and B2 and the CGCM3 with the A2and A1B scenarios. The SDSM can produce a largenumber of ensembles of output for each predictandso that several runs can be made for each scenario.This allows for an analysis of variability due to thedownscaling model alone.Many hydrologic models and assessments require thatclimate input data be available in sub-daily time steps,typically hourly. The disaggregation of daily data tohourly data is discussed in Section 6.5.6. This sectionalso discusses methods for generating future potentialevapotranspiration time series.6.5.4 Weather Generator MethodLARS-WG is a stochastic weather generator thatgenerates weather based upon the observed statisticalcharacteristics of weather at a site (Semenov and Barrow,2002: Weather Generator). Weather generators can beused to extend climate data time series, to simulatedata at sites that have no observations and to producehigh resolution climate scenario data for climate changeimpact assessments.Guidance:If possible, at least one future climate scenarioshould be generated using a weather generatorto examine climate variability. The GCM-emissionscenario used in the climate generator shouldmatch one of the scenarios chosen for the suiteof GCM-emission scenarios.The application of LARS-WG requires observed climatetime series for daily total precipitation, maximum andminimum daily air temperature and solar radiation (ifnecessary). Data can be formatted in a spreadsheet ascolumns of daily values of each parameter with timevalues.To develop future climates, LARS-WG requires daily timestep files of GCM simulated precipitation, temperatureand possibly, solar radiation for the current conditionsand the future period of interest (i.e., 2041 to 2070).LARS-WG uses the monthly summary GCM output toperturb predictor averages on a monthly basis as in thechange field method. It also uses the daily GCM outputto determine statistical characteristics of the currentand future time series to determine changes in futureparameter variability. Variability is dependent upon thechange in wet and dry day series lengths and changesin the monthly standard deviation of daily temperaturesand precipitation. Variability in solar radiation is notimportant in most hydrologic assessments.Visit the CCCSN website to download the required datafor the LARS-WG.• Click on Download Data on the left hand side of thescreen.• Select GCM from the drop down menu.• Click on Get GCM Temporal-Averages for themonthly summaries of parameter means.• In the chart Select longitude and latitude.