Seasonal and extreme precipitation characteristics for the watersheds of the Canadian Prairie Provinces as simulated by the NARCCAP multi-RCM ensemble

This study evaluates projected changes to characteristics of winter, spring, summer and fall seasonal precipitation and rain and snow dominated daily precipitation extremes for 47 watersheds, located mainly in the Alberta, Saskatchewan and Manitoba provinces of Canada, using a multi-Regional Climate Model (RCM) ensemble available through the North American Regional Climate Change Assessment Program. The set of simulations considered includes those performed with the six participating RCMs for the 1980–2004 period driven by National Centre for Environmental Prediction reanalysis II and those driven by four Atmosphere–Ocean General Circulation Models (AOGCMs) for the 1971–2000 and 2041–2070 periods. For precipitation extremes, regional frequency analysis is used to develop projected changes to selected 10-, 30- and 50-year return levels of rain and snow dominated extremes (i.e. RDEs and SDEs) separately. The uncertainties due to internal dynamics and physics of the RCMs and those due to the lateral boundary data from driving AOGCMs are studied at the watershed level and evaluated in terms of coefficient of variation on the basis of a multi-RCM ensemble. In general, the structural uncertainty appears to be larger than that associated with the choice of the driving AOGCM for most of the precipitation characteristics considered. Analyses of multi-RCM ensemble-averaged projected changes to mean seasonal precipitation and various return levels of RDEs and SDEs show an increase over nearly all the study domain. The changes to seasonal precipitation are not generally found statistically significant at 5 % significance level but those for RDEs and SDEs are found significant more often for return levels of smaller return period (10-year) compared to those of larger return period (50-year). It is expected that changes in seasonal and extreme precipitation characteristics will have important implications for managing regional water security-related issues in the Canadian Prairie Provinces.