Impacts of climate and forest changes on streamflow and water balance in a mountainous headwater stream in Southern Alberta

Abstract

Abstract. Rivers in Southern Alberta are vulnerable to climate change because much of the river water originates as snow in the eastern slopes of the Rocky Mountains. Changes in likelihood of forest disturbance (wildfire, insects, logging, etc.) may also have impacts that are compounded by climate change. This study evaluates the impacts of climate and forest changes on streamflow in the upper parts of the Oldman River in Southern Alberta using a conceptual hydrological model, HBV-EC in combination with a stochastic weather generator (LARS-WG) driven by GCM (Global Climate Model) output climate data. Three climate change scenarios (A1B, A2 and B1) are selected to cover the range of possible future climate conditions (2020s, 2050s, and 2080s). GCM projected less than a 10% increase in precipitation in winter and a similar amount of precipitation decrease in summer. These changes in projected precipitation resulted in up to a 200% (9.3 mm) increase in winter streamflow in February and up to a 63% (31.2 mm) decrease in summer flow in June. This amplification is mostly driven by the projected increase in temperature that is predicted to melt winter snow earlier, possibly resulting in lower water availability in the snowmelt dominated regions during the summer. Uncertainty analysis was completed using a guided GLUE (generalized likelihood uncertainty estimation) approach to obtain the best 100 parameter sets and associated ranges of streamflows. The impacts of uncertainty were higher in spring and summer flows than in winter and fall flows. Forest change compounded the climate change impact by increasing winter flow; however, it did not reduce the summer flow.