Hydro-climatic variability and extremes over the Athabasca River basin: Historical trends and projected future occurrence

Abstract

Since humans and ecosystems require adequate, reliable water supplies, hydro-climatic variability and extremes pose serious threats to society and the environment. Western Canada, including the Athabasca River Basin (ARB), is prone to considerable hydro-climatic variability including periodic extreme droughts and excessive moisture conditions. The main causes of these extremes are persistent, mid-tropospheric circulation patterns that disrupt expected precipitation and temperature. However, no investigation has specifically focused on the occurrence and causes of both past and future hydro-climatologic variability within the ARB. Assessment of the Standardized Precipitation Evapotranspiration Index (SPEI) reveals substantial inter-annual and decadal-scale variability over the entire ARB and its individual reaches, with no discernible trends during the last ~100 years. Evaluation of the 500-hPa circulation patterns associated with identified hydro-climatic extremes shows that major droughts are related to higher frequencies of distinctive ridging patterns over the ARB and fewer incidences of troughing. Excessive moisture conditions tend to have opposite patterns. Projections from several regional climate models reveal an average change toward more drought-like summer and slightly wetter annual conditions over the ARB, but there is a substantial range for individual models ranging from a considerable increase in drought with a higher degree of inter-annual variability, to relatively little change from current conditions. Simulated changes to key atmospheric circulations are consistent with these SPEI projections and indicate that those patterns associated with hydro-climatic extremes will continue in the future and in some cases, increase in frequency. Results from this analysis have quantified historical hydro-climatic variability in the ARB and have provided insight into potential future conditions as driven by changes to surface climate and synoptic-scale atmospheric circulation patterns.