Hydrologic modeling of the responses of two study watersheds to climate change is presented. The watersheds are the Upper Campbell and the Illecillewaet watersheds located in British Columbia. The first is a maritime watershed located on the eastern slopes of the Vancouver Island mountains; the second is located in the Selkirk Mountains in Eastern British Columbia. The Canadian Climate Centre General Circulation model has been used for the prediction of potential effects of climate change on meteorological parameters. In addition to the changes in the amounts of precipitation and temperature usually assumed in hydrologic climate change studies, other meteorological and climatic parameters also considered are the effect of climate on the spatial distribution of precipitation with elevation, as well as on cloud cover, glaciers, vegetation distribution, vegetation biomass production, and plant physiology. The results showed that the mean annual temperature in the two watersheds could increase by more than 3 degrees C and the annual basinwide precipitation could increase by 7.5% in the Upper Campbell watershed and by about 17% in the Illecillewaet watershed. The higher temperatures changed some snowfall to rainfall and the extra precipitation was mainly in the form of rain. The increase of the CO2 concentration caused stomata closure that reduced evapotranspiration. This effect was compensated by increased biomass in the Upper Campbell watershed, but not in the Illecillewaet watershed. These changes produced higher flows in winter and smaller flows in summer. The largest change in the hydrograph shape was in the Illecillewaet watershed where the mean annual maximum daily flow decreased by about 13% and its frequency was reduced. On the other hand, the mean annual runoff increased by 21%. In contrast, although the shape of the simulated annual hydrograph of the Upper Campbell watershed was not affected, magnitude and frequency of the annual maximum precipitation increased. Also, the mean annual runoff in the Upper Campbell watershed increased by 7.5%. These results indicate that different management procedures may be needed to minimize the effects of climate change on the water resources of the two climatically different watersheds and the regions that they represent.
