Author(s): Colin Clarke; Mike Hulley; Ed Watt
Keywords: No Keywords
Abstract: This investigation into trends in annual discharge of Canadian rivers focuses on long-term hydrometric stations having record lengths of at least 75 years. Eliminating stations with significant non-stationarities in mean annual discharge, and stations having evidence of a large diversion or a withdrawal, resulted in a final streamflow dataset of 113 Water Survey of Canada, WSC, hydrometric stations. In order to assist with the identification of potential factors contributing to a trend, at least one representative long-term climate station was selected for each long-term hydrometric station. A comprehensive trend assessment was completed on both annual discharge and precipitation (rainfall, snowfall, and total). Of the 113 long-term hydrometric stations, significant trend was identified at 21 sites: four associated with anthropogenic activities in the watershed, eight consistent with climate change (i.e. changes in annual rainfall, or annual snowfall or annual precipitation) and the remaining nine consistent with some combination of climate and anthropogenic activities. With respect to the climate stations, about 50% had a significant trend in total precipitation without a corresponding significant trend in annual discharge. The ratio of discharge stations with significant trend to climate stations with significant trend varied with ecoregion, from 0% to 40%. Factors contributing to this discrepancy include a possible compensating trend in evapotranspiration and a watershed that is relatively insensitive to small changes in precipitation.