Post-settlement drivers of streamflow variability in the Canadian Prairies: an analysis of the effects of the Anthropocene

The Canadian Prairies are home to 75% of Canada's irrigated agriculture. This is supported by the historically reliable streamflow regime in the South Saskatchewan River (SSR), which is initiated from snowmelt on the eastern slopes of the Rocky Mountains. This streamflow regime, however, is facing various changes. Most obviously, post-settlement water resource management in the prairies has intensively regulated the timing and volume of natural streamflows. Moreover, the natural streamflow regime in the SSR exhibits large inter-annual variability, influenced by the phases of Pacific Decadal Oscillation (PDO). Finally, some other sources of climate variability have recently resulted in significant shifts in the timing and volume of the regional streamflow, associated with changes in the form and timing of precipitation as well as variations in annual snow accumulation and melt in headwater catchments. By considering five unregulated and three regulated streams, we formally diagnose the post-settlement drivers of variability in the SSR's streamflow regime using various statistical tests. Our results show that long-term variations in the SSR streamflow timing and volume can be described by complex interactions among the PDO, human regulation and non-PDO sources of climate variability. For instance, human regulation can intensify the variations in annual streamflow volume during extreme PDO conditions, and non-PDO sources of climate variability can be masked by the effects of PDO and/or human regulation. Changes in the annual streamflow timing can be linked to human regulation and non-PDO sources of climate variability; in particular, human regulation is the main driver of recent dependence between annual streamflow timing and volume. Our findings have major importance for water security assessment in the Canadian Prairies and contribute to better understanding of feedbacks in coupled Natural-Human water systems during the current Anthropocene.