Dry spell characteristics over Canada in a changing climate as simulated by the Canadian RCM

Abstract

Dry spells, defined as extended periods of dry days, can serve as indicators of drought conditions, and are often used in the management of water resource systems, particularly for agriculture. In this study, the Canadian RCM (CRCM) projected changes to dry spell characteristics over Canada, for the April–September period, and their validation in current climate, are presented. Two CRCM integrations are considered; one validation integration for the 1961–2000 period and a transient climate change integration for the 1961–2100 period, corresponding to the SRES A2 scenario. The ability of the model to simulate dry spell characteristics, i.e. mean number of dry days, mean number of dry spells and selected return levels of maximum dry spell durations, and associated errors are assessed through comparison of integrations for the current 1971–2000 April–September period with those observed, derived from the observed precipitation records. Results suggest an underestimation of the mean number of dry days and 10- and 30-year return levels, while the model slightly overestimates the mean number of dry spells, at the grid-cell scale. Analysis of projected changes to dry spell characteristics for the future 2041–2070 and 2071–2100 periods, with respect to 1971–2000 period, suggests significant changes, particularly for the southern Prairies, where both mean number of dry days and return levels of maximum dry spell durations are projected to increase. Furthermore, combined analysis of changes to the amount of precipitation and mean number of dry days also suggests potential increase in drought conditions in future climates in this already drought-prone region for the April–September period. In addition to southern Prairies, this study also suggests significant changes to dry spell characteristics for other regions of Canada.