Climate and water availability indicators in Canada: Challenges and a way forward. Part II - Historic trends

Climate variability is recognized as an important influence on the availability of water throughout Canada, and projected climate change is anticipated to alter the amount, timing and distribution of water. This is Part II of a three-part (Parts I and III, this issue) analysis of water availability in Canada. Part II surveys current research, primarily Canadian in origin, on historical trends in climate and hydrologic indicators relevant to assessing water availability. Information on hydro-climate trends is not evenly distributed across Canada. Hydrologic trend research focuses on the North, British Columbia and the Prairies (Saskatchewan) with some research in Quebec, very little in Ontario and minimal analysis for Atlantic Canada. Overall, there is less research on trends in climatological indicators (drought, evapotranspiration, soil moisture); generally, the focus is on the Prairies. Hydrologic trends from basin-scale case studies are reported but inter-comparison is constrained by different periods of analysis. Trends vary by region. Generally, in the Prairies annual streamflow is decreasing, while results for the Yukon, BC, Ontario and Quebec are mixed. There is no clear signal on drought trends. Drought results are influenced by location, data (instrumental or paleo-climate), period of record and treatment of components in the drought index. For historic trend studies, observations with long duration, spatial coverage and minimal human-influences are crucial. These limitations in data affect streamflow assessment, but analysis of evapotranspiration and soil moisture trends is constrained by additional challenges of measurement, modelling and few data sets. Future research recommendations include combining climate change trend assessment with potential influences of large-scale atmospheric circulation patterns on inter-annual hydro-climatological variability. There is a need to explore the uncertainty associated with and methodological challenges in statistical analysis of hydro-climate time series. At present, there have been no rigorous detection and attribution studies of hydrology indicators in Canada.