Modelling climate change impacts on the hydrology of an agricultural watershed in southern Quebec

Spring flooding and water availability during the summer are two major concerns in southern Quebec. Climate change is expected to further exacerbate shortages of fresh water resources in Quebec. Therefore, the impacts of climate change on the hydrology of the Pike River watershed were projected for the 2041-2070 time horizon using a version of the Soil and Water Assessment Tool (SWATqc) adapted to Quebec's agroclimatic conditions. SWATqc was driven by inputs from four climate projections created with the fourth-generation Canadian Regional Climate Model (CRCM4) and the Arpege regional climate model. CRCM4 was driven at the border of its domain by three members of the Canadian Coupled Global Climate Model (CGCM3). The Arpege model, which has a variable grid, is not driven by another model. The gas emissions scenario used to drive climate models was scenario A2. Regional climate data sets were bias-corrected with the delta method prior to being used to drive SWATqc. Projected changes in precipitation and temperatures were analysed for their effects on evapotranspiration, surface and subsurface runoff, and streamflow. Mean annual streamflow was projected to increase between 9 and 19%. All future simulations projected significant increases or decreases in evapotranspiration, surface and subsurface runoff, and streamflow at the monthly time scale. Winter streamflow, for example, increased by 2- to 3-fold compared with the historical values. In addition, future spring floods started earlier and peaked in March instead of April. The four simulations were named ADC, ACU, AFA/AFD, and ARP. All but the ACU simulation projected a decrease in peak flow, while the ADC, AFD and ARP simulations suggested an increase. Although the majority of the simulations pointed to decreases in summer streamflows, the changes were not all significantly different from historical values. Results from this study not only show that climate change has a strong potential to exacerbate seasonal water availability and flooding issues in the watershed, but also provide conservative numbers that could be used in developing improved watershed management plans adapted to future climate change impacts.