The Vulnerability of Saskatchewan Water Resource System to Multi-Year Hydrologic Droughts at North and South Saskatchewan Rivers: Fusing Paleo Tree Ring Data with Stochastic Reconstruction

Abstract:

Despite having a semi-arid cold region, the province of Saskatchewan in western Canada is home to major agricultural activities. This is due to a reliable water supply in North and South Saskatchewan rivers (hereafter NSR and SSR), initiated from the Rocky Mountain headwaters in south western Alberta. The incoming interprovincial streamflow to Saskatchewan, however, is subject to significant annual variations due to natural climate variability, climate change as well as human use and regulation. Most importantly, severe multi-year hydrologic droughts in NSR and SSR have been observed within historical and paleo records. Such long-term low flow conditions can cause vulnerability in the water supply systems, particularly if combined with an increased irrigation demand, due to global warming, crop change, meteorological drought and/or irrigation expansion. This study aims at providing a novel use of long-term annual paleo streamflow records for monthly, multi-sector drought impact assessment. By considering tree ring-based reconstructed annual streamflow records, 10-year drought sequences with 100-year return periods were obtained at NSR and SSR. The annual sequences were converted to monthly flow hydrographs using a stochastic reconstruction scheme. The water resource system was then conditioned to multiple realizations of the monthly drought sequence and simulated under various scenarios for reservoir operation and increment in irrigation demand. Simulation results show that Saskatchewan can still maintain the Saskatchewan/Manitoba apportionment requirement, even under a 10-year drought and 10 folds increment in irrigation demand. Such severe drought sequence, nonetheless, cause significant decline in Saskatchewan’s hydropower production, which is currently the most profitable water sector in the province. Changes in reservoir operation, however, can considerably mitigate the adverse effects of drought and increased irrigation demand on hydropower industry, depending on the stage of drought, state of the system as well as the level of increment in the irrigation demand.