Simulating the hydrological impacts of climate change in the upper North Saskatchewan River basin, Alberta, Canada

► We study the impacts of climate change on streamflow in a mountain watershed. ► Five GCM scenarios were used in the ACRU agro-hydrological modeling system. ► Precipitation will increase strongly, actual evapotranspiration only little. ► Thus, streamflow will increase, especially baseflow, increasing winter flows. ► Summer and fall flows will decrease, further exacerbated by reduced glacier flows. The ACRU agro-hydrological modeling system provided the framework, containing code to simulate all major hydrological processes, including actual evapotranspiration estimates, to simulate the impacts of climate change in the Cline River watershed, Alberta, Canada, under historical (1961–1990) and a range of future climate conditions (2010–2039, 2040–2069, and 2070–2099). Whilst uncertainties in the estimation of many hydrological variables were inevitable, verification analyses carried out for the historical baseline period resulted in good to very good simulations of a range of hydrological processes, including daily air temperature, snow water equivalent and streamflow. Five climate change scenarios were selected to cover the range of possible future climate conditions. In order to generate future climate time series, the 30-year baseline time series was perturbed according to predicted changes in air temperature and precipitation. Projected increases in air temperature and precipitation resulted in mean annual increases in potential and actual evapotranspiration, groundwater recharge, soil moisture, and streamflow in the Cline River watershed. Increases in both high and low flow magnitudes and frequencies, and large increases to winter and spring streamflow are predicted for all climate scenarios. Spring runoff and peak streamflow were simulated to occur up to 4 weeks earlier than in the 1961–1990 baseline period. Predicted changes were simulated to progressively increase into the future. A clear shift in the future hydrological regime is predicted, with significantly higher streamflow between October and June, and lower streamflow in July–September.