SPEI-3 - Standardized Precipitation Evapotranspiration Index calculated for time scale of 3 months (Historical [1900-01 to 2005-11], 50th percentile)

Drought projections on seasonal to annual time scales are presented for Canada over the twenty-first century, based on the Standardized Precipitation Evapotranspiration Index (SPEI). Results make use of bias-corrected temperature and precipitation projections from 29 global climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), and include three different forcing scenarios (RCP2.6, RCP4.5 and RCP8.5). Large differences in projected drought changes are observed among different regions. On the annual time scale, southwestern Canada and the Prairies may experience an increase in drying under a warmer climate. On the other hand, coastal regions, including northern Canada, the northwest Pacific coast and the Atlantic region, show a small increase in wetness. Winter and spring SPEI results depict an increase in wetting, reflecting the projected country-wide winter and spring precipitation increases under climate change. For the most part, autumn and summer show increases in drying. The largest relative changes in both summer drying and winter wetting were found over northern regions, but the offsetting seasonal effects typically balance out to yield various degrees of wetting on the annual scale for this region. The projected drought responses are relatively modest in the low forcing scenario (RCP2.6) for most Canadian regions. In addition, even for regions most affected, a marked increase in surface water deficit might not occur until the second half of this century. Inter-model variation (a crude measure of projection uncertainty) typically increases with forcing intensity and lead time, and is generally greater in northern and western Canada.