ClimateChange Assessment Guide.pdf - University of Waterloo

Background7Figure 2.1 Estimated probabilities for a mean surface temperature change exceeding 2°C in 2080 to 2099 relative to 1980to 1999 under the mid-range GHG emission scenario (SRES A1B scenario). Results are based on a single GCM (a, c), and amultiple GCM mean (b, d), for winter (a, b) and summer (c, d). ((Meehl et al., 2007 811) Climate Change 2007: The PhysicalScience Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on ClimateChange, Figure 10.30. Cambridge University Press)is likely to decrease. The snow season length and snowdepth are expected to decrease except in northernmostCanada where the maximum snow depth will likelyincrease (Christensen et al., 2007b).The notable spatial distribution of temperature andprecipitation changes for North America is shown inFigure 2.2. The annual, winter (December, January,February or DJF), and summer (June, July, August orJJA) temperature and precipitation changes (between1980 to 1999 and 2080 to 2099) were averaged for 21GCMs for a mid-range or intermediate GHG emissionscenario (i.e., SRES A1B, see Section 3, Table 3.1 fordefinitions). There is greater warming in winter in thenorth while, in summer, the greatest warming occursin the continental interior. In winter the maximumprecipitation increase approaches +50% in thenorth while in summer it is about +20%. However, insummer there is a large portion of North America - thecontinental interior - where precipitation decreases; thiscorresponds with the area that is likely to experiencethe greatest warming (Christensen et al., 2007b). Thiscombination has important implications for wateravailability for much of North America. Changes inclimate are very likely to have significant impactson hydrology such as more frequent high-intensityprecipitation events and more prolonged and severeperiods of drought. Those projected changes in globalclimate that are relevant to water availability and waterresources planning and management are summarized inTable 2.3.