Streamflow Variability (1965 to 1998) in Five Northwest Territories and Nunavut Rivers

In Canada, the Northwest Territories and Nunavut have been characterized as two regions prone to anthropogenically-forced climate change. This study focuses on identifying trends in streamflow on selected rivers in the two territories. Streamflow data from five Water Survey of Canada hydrometric stations were analyzed, with the assumption that there are trend, cyclic and stochastic components in the 1965–1998 time series. Only two statistically significant linear trends in mean annual streamflow, spring freshet timing or magnitude were identified. Warmer early spring temperatures were found to bring earlier spring freshets in mainland Nunavut. Neither exhibited linear trends from 1965 to 1998. Increasing summer temperatures in the Northwest Territories have not resulted in increases in evapotranspiration and a decrease in water available for runoff, perhaps because of feedbacks which stabilize the hydrologic regime. The cyclic trends in many of the time series are related to the Pacific Decadal Oscillation (PDO) index, which is a measure of north Pacific sea surface temperatures and sea level pressure. There was a six year lag between a mid-1970s shift to a warm PDO phase and wetter conditions in arctic rivers. This lag was extended to ten years at the subarctic rivers because of higher storage demands after the 1965–1975 dry period. The lack of a linear trend in the PDO index between 1965 and 1998 corroborates the lack of linear trends in the mean annual streamflow time series. In light of the findings, further research is recommended on the nature of possible hydrologic feedbacks that control northern runoff regimes and the processes which link north Pacific temperature and northern Canadian streamflow regimes.