ClimateChange Assessment Guide.pdf - University of Waterloo

Appendix E E-41Subwatershed 19 Case StudyStreamflow rates simulated with HSP-F for the current climate and the nine Percentile Method future climates areshown in Figure 6-3. All nine future climates have streamflow distributions that follow a similar trend as the baselineclimate; peak spring flows receding to summer low flows, which then recover through the fall. However, the timing ofthe decline in flow from the spring to the summer is shifted to earlier in the year. This seasonal shift is due to warmerwinter temperatures which lead to less snowpack and earlier spring snowmelt. In addition, the majority of futureclimates will cause winter streamflow increases of up to 50%. Increases in winter streamflow are primarily caused bya shift to more winter precipitation occurring as rainfall, rather than snowfall, and more winter precipitation in general. Figure 6-3:HSP-F mean monthly streamflow with GCM climate change scenarios.To illustrate potential effects of climate change on low flows, a histogram of the projected changes in 7Q 20 is shown inFigure 6-4. The 7Q 20 is the lowest 7-day average flow that occurs once every 20 years and is a commonly used as alow flow index, particularly for regulating the discharge of wastewater (e.g. WPCP effluent). As shown in Figure 6-4,five out of nine scenarios predict up to a 10% increase in the 7Q 20 . An increase in the 7Q 20 suggests that the amountof streamflow that is reliably generated by Subwatershed 19 will increase. This increase is likely due to the majority ofnine GCM future climates having overall increases in precipitation. Figure 6-4:Histogram of 7Q 20 streamflow with GCM climate change scenarios.