ClimateChange Assessment Guide.pdf - University of Waterloo

Guide for Assessment of Hydrologic Effects of Climate Change in Ontario726.4.3.3 Analysis of ResultsAll 57 future climates encompassing the full range ofGCMs and emission scenarios were modelled usingHSP-F to explore the range of hydrologic effectsassociated with these climate change scenarios (thefull range of results are reported in Appendix C).The range of outcomes from the full suite of futureclimates are compared with the range of results fromthe two screening approaches to illustrate the range ofinformation available to the assessment process andthe potential implications for decision making and riskassessment. Even though 57 climate change scenariosprovide a very wide range of future climates to assess,they still do not include all available scenario outputsand therefore do not capture all the potential outcomes.Figures 6.4, 6.5, and 6.6 present mean annual waterbalance estimates for 4 scenarios (i.e., scatter plotcandidates), 8 scenarios (i.e., percentile candidates)and 57 scenarios, respectively. The 4-scenario approachcaptures the extreme outcomes for surface runoff andgroundwater recharge, but the 8-scenario approachcaptures the distribution in surface runoff andgroundwater recharge.The mean monthly runoff (2050s) for silty soils for thetwo scenario screening approaches and the full suite offuture climates is shown in Figure 6.7. The 4-scenarioapproach captures the range and distribution of runoffvalues reasonably well while the 8-scenario approachdoes not capture the increase in runoff in the winter andearly spring displayed in some scenarios. This may bedue to only choosing the 90th and 10th percentile; moreextreme percentiles (i.e., 95th and 5th percentiles) maybe more appropriate. The two scenarios with anomalousresults in the 57-scenario plot are: ID23 - GISSE-R, SR-A2and ID24 - GISSE-R, SR-B1.6.4.3.4 Recommended Approach to Scenario SelectionThe climate scenario selection methods outlineddo not recommend a set series of GCMs and GHGemission scenarios that should be used for hydrologicassessments; rather, the focus is on developingapproaches that provide the widest range of possibleclimate change conditions to assess the widest range ofpossible hydrologic outcomes for planning and decisionmaking. The goal is to understand the uncertainty andbuild more resilient watersheds.Guidance:The scatter plot method is not of sufficient detailto allow the users to draw statistically basedconclusions on the results. Therefore, the scatterplot method is not recommended.Guidance:It is recommended that all studies select 10 GCMclimate scenarios according to the PercentileMethod. This method provides a statisticaljustification for scenario selection and a rationalefor explaining results based upon the prevailingtrends in the outcomes. The approach shoulduse the 95th, 75th, 50th, 25th and 5th percentilesfor mean annual change in temperature andprecipitation to explore the broad range of futureclimates.The user should also select any additionalclimate scenarios that are required to supportdownscaling (for investigating variability).If downscaling methods (Section 6.5.3-6.5.5) areundertaken, it is recommended that the GCM and GHGemission scenario associated with the downscalingtechnique also be used and applied in a change fieldmethod (Section 6.5.2) to allow for a comparison ofvariability in the results from these methods. This set ofGCM scenarios will provide a basis for examining therange and likely future trends in the outcomes.The application of as many scenarios as possible (i.e., 57or more) in an impact assessment offers the benefit ofexploring a wide range of hydrologic impacts and helpsto define the extremes and the predominant trends fromthe scenarios. This approach is favoured when resourcespermit.