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The potential impacts of the future climate change on the causes of flood flows were investigated for two mountainous watersheds located in two different climatic regions of British Columbia. The Canadian Centre for Climate Modeling Analysis General Circulation Model (CGCMa1) has been used to estimate changes in the precipitation and temperature. The UBC Watershed Model (Version 4.0) was used to simulate the discharge of the two study watersheds and to identify the causes of peak flows. In the simulations, apart from changes in precipitation and temperature, changes in the spatial distribution of precipitation with elevation, cloud cover, glacier extension, vegetation distribution, vegetation biomass production, and plant physiology were considered. The results showed that the future climate for the two study watersheds would be wetter and warmer than the present climate. The majority of the flood events in the coastal rainfed watershed of Upper Campbell are and would be generated by fall rainfall events and winter rain-on-snow events, whereas in the interior snowcovered Illecillewaet basin the floods are and would be produced by spring rain and snowmelt events and summer events. The analysis indicated that the overall flood magnitude and frequency of occurrence in the Upper Campbell watershed would increase. On the other hand, the number and the magnitude of the flood flows would decrease under the future climatic conditions in the Illecillewaet basin. Based on these findings, different management practices should be applied in the two watersheds to overcome the effects of the future climate change. [Copyright &y& Elsevier]