Future changes in intensity and seasonal pattern of occurrence of daily and multi-day annual maximum precipitation over Canada

SummaryDaily and multi-day extreme precipitation events can cause important flooding. Assessment of the future evolution of heavy precipitation is therefore crucial in a context of climate change. Simulation results for Canada from the Canadian Global Climate Model (CGCM3) have been analyzed for 1 to 5-day annual maximum (AM) precipitation events over the 1850–2100 period using simulation series from five ensemble members. Trend analysis showed that daily and multi-day intense precipitation series were stationary over the 1850–1980 period while trends emerged during the period 1980–2005. Probabilities of occurrence of AM precipitation for the various months were also estimated. For the historical climate (1850–1980), a comparison with observed data suggested that the model adequately reproduced the observed regional patterns of seasonal occurrence of AM events. Future projections suggest that, for many Canadian regions, a shift will take place from summer to spring and/or autumn in the seasonal occurrence of AM precipitation events. Moreover, statistical frequency analysis of models series suggests that daily and multi-day events will be more intense and frequent in a future climate for all regions except the Prairies. In some regions (e.g. west coast of British Columbia), the return period associated with a given precipitation intensity in historical climate will decrease by a factor of five over the 2080–2100 period. No significant differences have been observed between daily and multi-day projections for intensity/frequency occurrence of AM events.