ClimateChange Assessment Guide.pdf - University of Waterloo

Climate Change Assessment65Guidance:Scenario runs should use the 2050s time horizonif resources limit the assessment to one timeperiod.The 2050s time horizon is far enough in the future thatthe changes in climate are likely to be sufficiently largeto see notable impacts emerge. This time frame isappropriate for both a strategic planning approach anda risk framing and assessment approach in which theimpact assessment information is used to build resiliencein the system or expand the coping range throughadaptation. At this point in the future, the climate systemresponse to the different emission scenarios is beginningto diverge. Also, the most recent RCM output is currentlyonly available for the 2040 to 2070 period.The 2020s time horizons are used for numerous planninginitiatives; however, we do not recommend using thistime period as the only climate change scenario. Thistime period is not as likely to produce large changes inclimate and hence produce potential climate changeimpacts. It may be useful, however, for establishing anintermediate assessment of potential impacts, as theemission scenarios remain relatively similar throughoutthe 2020s period; and for informing the development ofan impact monitoring program and for indicating whenadaptations may need to be implemented.The 2080s period is useful for long-term strategicplanning; some municipalities and agencies areundertaking 100-year planning exercises (e.g., GreatVancouver District) where incorporating this climateimpact information would be warranted.6.4.3 Selecting the Number of Climate ChangeScenariosGuidance:The IPCC recommends that users shouldapply multiple climate change scenarios – asmany as possible - in impacts and adaptationassessments.From the knowledge-generating perspective, thechallenge remains determining how many scenariosshould be used to gain understanding of:• The potential range of impacts that may occur;• The potential effects that may be outside currentconditions or the coping range;• The range of risks; and• The range of future conditions that adaptationstrategies should accommodate to build resilience/robustness in watersheds.Practical considerations also exist when choosing thenumber of scenarios; they include the following:• The capabilities of those undertaking the impactassessment to incorporate a large number ofscenarios into the modelling process. This includesthe availability of tools to manipulate and analyze thelarge amounts of data generated.• Interpreting and explaining the results generatedfrom multiple scenarios for those who must integratethe climate change impact assessment informationinto the decision making and policy making process.This section explores two candidate approaches forshort-listing climate change scenarios. This follows theoriginal screening for the case study that identified 57GCM- GHG combinations as candidates for developinginto climate change scenarios for hydrologic assessment.The proposed approaches include:• The scatter plot method - ‘bounding the uncertainty’(4 candidate scenarios); and• The percentile method (maximum 10 candidatescenarios).The initial screening of the GCM-GHG climate scenariosused in the Guide, as outlined in Section 6.4.2 above,focused on the availability of parameters that arecritical for hydrologic modelling. Thirty-nine of 57 futureclimates had monthly change fields for temperature,precipitation, wind speed and solar radiation (ID 1 to 39).Eighteen additional future climates were included eventhough there were no wind speed change field data (ID40 to 57). These additional future climates incorporatea broader range of GCMs (i.e., HadCM3 A2 informationthat could be linked to downscaling efforts that werebeing considered as part of the scenarios package).