ClimateChange Assessment Guide.pdf - University of Waterloo

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Guide for Assessment of Hydrologic Effects of Climate Change in Ontario34Table 4.1 Summary of general advantages and disadvantages of GCM-change field, synthetic, analogue anddownscaled climates for use in assessmentsTechnique Description Advantages DisadvantagesGCM-change fieldSynthetic andAnalogue ScenariosStatisticalDownscaling withRegressionWeatherGeneratorsRegional ClimateModels• Simulated climate at coarsegrid spacing• Use to develop monthly(seasonal or other) changefields• Provides data used instatistical downscaling• Wide variety of GCMsavailable• Artificial or based on spatialor temporal transposition ofclimates• Climates based uponstatistical relationshipsbetween climate variablesand atmospheric predictors• Weather data generatedbased on statistical attributesof local climate and GCMvariables• Higher resolution physicallybased models oftenembedded in GCMs• Local physiography and waterbodies are included• Several GCMs have beenapplied to long-termsimulations for family ofemission scenarios• Comprehensive physicallybased tools• Several variables available• Good agreement across GCMson temperature change• Can be realistic if well informed• Complete sets of variablesrelevant to hydrology may bereadily available• Supports examination ofsensitivity and vulnerability• High spatial and temporalresolution if observational dataavailable• Several variables available• Ease of application, thus manylong-term scenarios can betested• Good skill demonstrated atsimulating temperature• High spatial and temporalresolution if observational dataavailable• Several variables available• Ease of application, thus manylong-term scenarios can betested• Good skill demonstrated atsimulating temperature• Good skill at simulating periodsof drought and extendedprecipitation• High spatial and temporalresolution output for severalvariables• Improved extreme eventsimulation over GCMs• Physically based and consistentwith GCMs• May account for feedback fromanthropogenic or natural systems• Coarse spatial resolution,unrepresentative of local climate• Extreme events generally occurat a smaller scale than GCMscales, not represented• Modest agreement across GCMson precipitation• Cannot be used to changeclimate variability• Not related to SRES scenarios• Usefulness limited to smallerchanges• Analogues for enhanced GHGconditions likely not available• May be physically implausible• Assumes empirical relationshipswill hold as climates change• May perpetuate GCM biases• Generally underestimatesextremes• Some models do not simulatemonthly variability well• Poor skill in simulatingprecipitation extremes• Neighbouring stations notcorrelated• Observational data to buildstatistical relationships notavailable in all areas• Assumes empirical relationshipswill hold as climates change• May perpetuate GCM biases• Generally underestimatesextremes• Some models do not simulatemonthly variability well• Poor skill in simulatingprecipitation extremes• Neighbouring stations notcorrelated• Observational data not availablein all areas• Few model runs and GHGemission scenarios available• May perpetuate GCM biases• Complex model systemsprecludes non-expert use• Simulation periods are typicallyshort, thus fewer extremes arerepresented
Hydrological Impacts5. Hydrologic Impacts35This section discusses climate change from a waterresources perspective. It identifies some water resourceclimatechange studies conducted in Ontario and alsoprovides a review of fundamental hydrologic processesand the effects of climate change.The hydrologic cycle describes the pathways thatwater takes as it moves between the atmosphere, landsurface, subsurface and surface water bodies. Thesepathways, representing hydrological processes, resultfrom the interaction of climatic, geologic and ecologicconditions. The radiation energy from the sun initiatesthe hydrologic cycle by evaporating water from the landand oceans. The water vapour enters the atmosphere,is transported by air masses and condenses to formclouds. The clouds produce precipitation in the form ofrain or snow. Precipitation falls on land surfaces, initiallywetting the surfaces (wetting includes interceptionby vegetated surfaces). If sufficient rain or snowmeltoccurs surface depressions are filled and overlandrunoff moves downslope to reach stream channels. Theremaining water at the land surface, after accountingfor runoff, either evaporates from the wetted surfacesor infiltrates below the ground surface where it is stored(soil water storage) or seeps down to the watertable andrecharges groundwater. Soil water storage is depletedby evapotranspiration. Groundwater storage is depletedby downslope flow to locations where groundwaterdischarges to the land surface.Climatic conditions are the driving forces of thehydrologic cycle. As such, climate change that altersthe historic pattern of variation in climate will impact allcomponents of the hydrologic cycle, both in terms oftiming and quantity. Changes in seasonality, variabilityand extremes will be more disruptive than averagechanges (Smith et al., 2005).The impacts of climate change on surface waterresources are directly experienced in all componentsof the water balance, while the impacts to groundwaterresources are experienced through water rechargereaching the aquifer (Loaiciga, 2003). Due to therelatively greater amount of water in the ground than onthe ground surface, the rates of change due to climatewill be slower and less influenced by short term events.Consequently, relative to surface water resources,aquifers are buffered from the effects of a changingclimate, and as such will become an increasinglyimportant resource (Chen et al., 2004). It is important torecognize, however, that groundwater and surface waterare essentially a single resource (Winter et al., 1998);impacts to any hydrological process will influence allother hydrological processes. For example, any increasein consumptive groundwater use has consequenceson streamflow for watercourses receiving groundwaterdischarge from the same aquifer.In general, an increase in temperature is expected toelevate potential evapotranspiration rates, diminishsnowpack accumulation and reduce the number offreezing days leading to seasonal increases in infiltration.An increase in the frequency of severe storms promotesincreased amounts of surface runoff. In other words,climate change is likely to intensify the extremes inhydrological cycle processes (Loaiciga et al., 1996).Consideration also needs to be given to societalresponses to changing climatic conditions as changes inwater demand and land use practices can also alter thelocal and regional behaviour of hydrologic systems.5.1 Studies Completed in OntarioSeveral climate change impact assessment studies havebeen completed within the Province of Ontario. Thefollowing sections describe the investigations, theirmethodology and results, and some identified gaps.5.1.1 Credit Valley Conservation (CVC) (Walker andDougherty, 2008)As part of the CVC Water Management Strategyprocess, a Hydrological Simulation Program-FORTRAN(HSP-F) based surface water flow and water qualitymodel (Bicknell et al., 2001) was setup and calibratedat the watershed level. Several scenarios representingfuture conditions were devised to test the sensitivity ofthe watershed to further urbanization and to variouswater management strategies. In addition, two climatechange scenarios were developed and used as input forsimulations. The GHG scenarios were from the familyof SRES scenarios (Table 3.1) and were based upon thesimulation results from two GCMs, the Canadian CGCM2and the UK HadCM3, for the 2050s. These GCM-GHGruns were selected to represent the largest projectedchanges in air temperature and precipitation and thus,bracketed the larger group of GCM-GHG emissionscenario combinations. The scenarios represented warmand drier conditions (CGCM2) and warmer and wetterconditions (HadCM3) in annual average terms.
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Guide for Assessment of HydrologicE
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Appendix A A-1Watershed and Receivi
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Appendix B B-1GCM Modelling GroupsT
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Appendix CGCM-Based Change FieldAss
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Appendix E E-1Subwatershed 19 Case
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