No abstract

A stochastic weather generator based on the WGEN model has been tested on 13 meteorological stations in Quebec, Canada. The generator, called WeaGETS, accounts for longer persistence of wet and dry spells by including second and third order Markov chain models. It also includes regional correction factors to adjust the precipitation percentile values as simulated by the WGEN model with respect to observed precipitation. This is a first step toward the development of a model to construct basin scale projections of future changes in climate intended for hydrological impact studies. A direct validation of the generator using selected extreme indices of precipitation has shown that the modified generator generally performed better than WGEN at simulating daily precipitation distribution, quantity and occurrence. Some discrepancies still remained or were amplified which appear to be season-related, suggesting recourse to seasonal correction factors. However, because the generator is aimed at developing climate change projections, no additional parameters were introduced in the model to keep it as parsimonious as possible. WeaGETS was indirectly validated by conducting a series of hydrological modelling experiments on the Châteauguay River Basin located in southern Quebec. Results of the simulations show that WeaGETS was able to adequately represent the duration of summer low flow events as well as the annual direct runoff. However an overestimation of the peak flows was observed for the more extreme flood events with return periods exceeding 50 years. Whether or not such an overestimation is solely caused by the generator overestimating extreme precipitation events and/or consistent combinations of precipitation and temperature needs to be further addressed through additional modelling experiments on various watersheds and with more observed climatic data before drawing definitive conclusions. Résumé