Paleo‐Hydrological Drought in the South Saskatchewan River Basin: Implications for Water Allocation and Management

ABSTRACT

The South Saskatchewan River Basin (SSRB) in southern Alberta is the only major Canadian watershed where water supplies are effectively fully allocated. This was the first region targeted for land‐use and water‐supply planning under new provincial legislation. This paper examines water allocation and management in the SSRB from the unique perspective of 900 years of annual river flow in the four major sub‐basins. We reconstructed annual runoff from a dense network of 192 ring‐width chronologies, many in the headwaters of the runoff‐generating sub‐basins. We employed a regression approach to building tree‐ring models of runoff, where the predictors are principal components that capture the dominant hydroclimate signals in a large set of chronologies. The stepwise regression models performed well over a 54‐year calibration period with a mean R ² (among all sub‐basins) of 0.71. The paleohydrology includes at least five prolonged hydrological drought events over the past nine centuries, with the most persistent occurring between 1840 and 1880. While severe droughts have occurred in recent decades, those of the longest duration predate gauge records. Therefore, dendrohydrological evidence suggests that relying solely on modern streamflow records to inform water management and infrastructure planning in the Canadian Prairies may underestimate future drought risks.