An assessment of historical and projected future hydro-climatic variability and extremes over southern watersheds in the Canadian Prairies

Since human activities and ecosystem health require adequate, reliable water supplies, hydro-climatic variability and extremes pose serious threats to society and the environment. Previous studies have shown that the Canadian Prairies normally experience considerable hydro-climatic variability, including periodic droughts and excessive moisture conditions, which are mainly caused by mid-tropospheric circulations that disrupt expected precipitation and temperature patterns. However, no investigations have specifically focused on both past and future hydro-climatology over watersheds within the region. Evaluation of the Standardized Precipitation Evapotranspiration Index reveals considerable inter-annual and decadal-scale variability over the study regions of the Oldman and Swift Current Creek Watersheds, with no discernible trends during the last approximate to 100years. There is also an indication of increased variability since the mid-1980s. Assessment of the 500hPa circulation patterns associated with identified hydro-climatic extremes shows that major droughts are related with higher frequencies of distinctive ridging patterns over the Prairie region, and lower incidences of zonal/troughing patterns (the former significantly increasing over the last 60years). Excessive moisture conditions have opposite patterns. Projections from two (a drier/warmer and wetter/cooler) Regional Climate Models indicate an uncertain future in the selected watersheds ranging from a substantial increase in drought with a higher degree of inter-annual variability, to relatively no change from current conditions. Furthermore, future changes to key atmospheric circulations suggest that those patterns associated with extreme dry conditions will continue in the future and in some cases, increase in frequency. Results from this analysis have improved the understanding of historical hydro-climatic extremes in western Canada and have provided insight into potential future occurrences of these extremes as driven by changes to key surface climate and synoptic-scale atmospheric circulation patterns.