Uncertainties in long-term drought characteristics over the Canadian Prairie provinces, as simulated by the Canadian RCM

Projected changes to the severity, frequency and duration of long-term droughts for 47 watersheds in the Canadian Prairie provinces, as well as uncertainties associated with the lateral boundary forcing data and choice of drought index are explored using an ensemble of Canadian Regional Climate Model (CRCM) simulations for current (1971-2000) and future (2041-2070) climates. Drought characteristics are defined using 2 drought indices: the precipitation anomaly based Drought Severity Index (DSI) and the more complex Palmer Drought Severity Index (PDSI). Forty-seven watersheds were subjectively classified as northern (15) and southern (32) watersheds to examine regional differences. Comparison of CRCM simulated drought characteristics with those observed suggests that the model has difficulties in reproducing observed severity, frequency and duration of drought events, particularly those based on PDSI. Projections show a decrease in severity, frequency and duration of long-term droughts for the majority of the northern watersheds, and an increase for the southern watersheds for DSI-based drought, while the majority of the 47 watersheds experience increasingly severe and prolonged droughts according to PDSI-based assessment. Uncertainties associated with the choice of drought index are larger for the northern watersheds compared to the southern watersheds. For DSI-based drought uncertainties associated with the CRCM, driving data are larger for southern watersheds only, whereas for PDSI-based drought the uncertainties are large for most watersheds. In general, uncertainty associated with the choice of drought index is as important as uncertainty in the CRCM simulated data. Nevertheless, a trivariate classification based on changes to various drought characteristics derived from the ensemble mean of CRCM simulations shows worsening DSI-based drought for southern watersheds and worsening PDSI-based drought for the entire Praries, thus posing challenges for regional water resource management.