ClimateChange Assessment Guide.pdf - University of Waterloo

Guide for Assessment of Hydrologic Effects of Climate Change in Ontario646.4.2.3 Performance of GCMs in Replicating CurrentClimateAnother criterion proposed to assist in screeningof GCMs for scenario development is to assess theperformance of the GCMs in replicating the 20thcentury climate or significant climatological features(e.g., mean annual temperature patterns or monsoonrains in the tropics). The research in this area is justbeginning and there is no clear guidance on theobjective measures to use. However, it is important toevaluate a broad spectrum of climate processes andphenomena (Gleckler et al., 2008) as the use of a singleindex of model performance may be misleading andhide the more complex picture of the relative meritsof the GCMs. The accurate simulation of one aspectof climate does not ensure accurate representationof other features. Research is attempting to developa suite of metrics to characterize model performanceand then to identify subsets of these metrics thatare relevant for selected applications. In Canada,preliminary development work is underway as part ofthe CCCSN to assess the performance of GCMs usingtemperature and precipitation metrics, but these resultsare not yet available (Neil Comer, Environment Canada,pers. comm.). Therefore, for now all GCMs can beconsidered relevant candidates; however, users shouldnote that the FGOALS-g1.0 model had a cold bias inthe high latitudes of the Northern Hemisphere (see theexplanation for the bias and the corrections that weremade at:http://www-pcmdi.llnl.gov/ipcc/model_documentation/more_info_iap_fgoals.pdf).6.4.2.4 Availability of Critical Atmospheric Parametersfor the Hydrologic Assessment ApplicationThe basic modelling elements necessary for hydrologicassessment applications include:• Air temperature; and• Precipitation.Other parameters that can enhance the input suite forhydrologic modelling include:• Solar radiation;• Wind speed; and• Relative humidity.While these five parameters are part of the climatemodelling process in the GCMs, the critical issueis whether they are archived, formatted and madeavailable to users via the IPCC data distribution site andspecifically, in this case, the CCCSN website. When thisGuide was undertaken, the solar radiation data from theAR4 runs were not available on the CCCSN website andthese data had to be formatted and uploaded to thesite for our application. In situations where wind speedand relative humidity change fields are not available,hydrologic modelling with future climates can beundertaken without changes to these parameters.Some of the climate modelling centres (i.e., CanadianGCM - CGM3T47 model) have undertaken ensembleruns for selected emission scenarios – that is multipleruns of the GCM using different initialization conditionsbut the same SRES emission scenario. These ensembleruns provide insight into the internal variability ofthe climate system represented in one GCM. It is notrecommended that the ensemble mean from these runsbe used in impact assessments as it may not meet thephysical plausibility criterion (combination of changesin different variables should be physically consistent)identified by the IPCC; however, individual ensembleruns can be used.6.4.2.5 Selection of Baseline Period and Future TimePeriod for the GCM ComponentFuture time periods including the 2020s, 2050s and2080s (representing the periods 2011-2040, 2041-2070and 2071-2100, respectively) and the baseline periodof 1961 to 1990 (and 1971 to 2000) have been preprocessedand are available on the CCCSN website.There is capacity for users to define their future timeperiods and base climate period on the CCCSN sitebut, for most applications we recommend using thepre-defined periods to maintain consistency andcomparability across hydrologic assessments. However,there is a circumstance where changing the baselineperiod for the GCM would be warranted. It would berelevant to do so if the baseline data for the assessmentdoes not have sufficient overlap with the 1961 to 1990(or 1971 to 2000) GCM-based climate reference period,either the observed climatological baseline data arefor a much earlier period or a much later period, forexample, 1981 to present.