Canadian RCM Projected Changes to Extreme Precipitation Characteristics over Canada

Changes to the intensity and frequency of hydroclimatic extremes can have significant impacts on sectors associated with water resources, and therefore it is relevant to assess their vulnerabilities in a changing climate. This study focuses on the assessment of projected changes to selected return levels of 1-, 2-, 3-, 5-, 7- and 10-day annual (April September) maximum precipitation amounts, over Canada, using an ensemble of five 30-yr integrations each for current reference (1961-90) and future (2040-71) periods performed with the Canadian Regional Climate Model (CRCM); the future simulations correspond to the A2 Special Report on Emissions Scenarios (SRES) scenario. Two methods, the regional frequency analysis (RFA), which operates at the scale of statistically homogenous units of predefined climatic regions, with the possibility of downscaling to gridcell level, and the individual gridbox analysis (GBA), are used in this study, with the time-slice stationarity assumption. Validation of model simulated 20-, 50- and 100-yr return levels of single- and multiday precipitation extremes against those observed for the 1961-90 period using both the RFA and GBA methods suggest an underestimation of extreme events by the CRCM over most of Canada. The CRCM projected changes, realized with the RFA method at regional scale, to selected return levels for the future (2041-70) period, in comparison to the reference (1961-90) period, suggest statistically significant increases in event magnitudes for 7 out of 10 studied climatic regions. Though the results of the RFA and GBA methods at gridcell level suggest positive changes to studied return levels for most parts of Canada, the results corresponding to the 20-yr return period for the two methods agree better, while the agreement abates with increasing return periods, that is, 50 and 100 yr. It is expected that the increase in return levels of short and longer duration precipitation extremes will have severe implications for various water resource related development and management activities.