ASSESSMENT OF FUTURE CHANGE IN INTENSITY-DURATION-FREQUENCY (IDF) CURVES FOR SOUTHERN QUEBEC USING THE CANADIAN REGIONAL CLIMATE MODEL (CRCM)

Abstract

Intensity–duration–frequency curves are used extensively in engineering to assess the return periods of rainfall events. The estimation and use of IDF curves rely on the hypothesis of rainfall series stationarity, namely that intensities and frequencies of extreme hydrological events remain unchanged over time. It is however expected that global warming will modify the occurrence of extreme rainfall events. In order to assess how extreme rainfall events will be modified in a future climate, an analysis of the Canadian Regional Climate Model (CRCM) simulations under control (1961–1990) and future (2041–2070) climates was performed. May to October annual maximum (MOAM) rainfall for 2-, 6-, 12- and 24-h durations were extracted and analyzed using regional frequency analysis for grid boxes covering the Southern Quebec region. Comparison with available rainfall records shows that CRCM estimates are consistent with those based on observed data considering the different spatial scales related to observed data (meteorological stations) and to simulated ones (grid boxes). Comparison of regional estimates in control and future climate at the grid box scale reveals that return periods of 2- and 6-h events will approximately halve in future climate while they will decrease by a third for 12- and 24-h events. Regional IDF curves at the grid box and the station scales are proposed. The analysis of spatial correlation of simulated MOAM series in control and future climates for the region under study suggests that, for a given duration, spatial correlations will decrease in a future climate suggesting that annual extreme rainfall events may result from more convective (and thus more localized) weather systems. Multi-model ensemble systems (different GCMs with different RCMs) as well as multi-member ensembles (investigation of possible sensitivity to initial conditions) are needed to investigate the impact of model structures on future change in extreme rainfalls.