Precipitation

Projected changes in precipitation in BC are expected to be relatively minor, especially when compared to the historical variability in the province. The Pacific Climate Impacts Consortium (PCIC) projections show that annual precipitation may increase by about 9% by the end of the 21st century, relative to the 1961-1990 baseline (see MaPP region Summary Table), while summer precipitation is projected to decrease by 10% [27,28].

Wetter winters are projected to lead to increased runoff in rivers and streams in the winter. Less precipitation will fall as snow in the winter, which is likely to result in a reduction of the spring snowpack by 55% by 2050 [41]. Glacial runoff in the spring has already declined in southern BC, and this is projected to occur for northern BC glaciers through 2050 and beyond [10,42]. Due to this reduction in snowpack, the spring freshet will likely occur earlier in the spring in many rivers. By the end of the century, spring streamflow will likely have increased significantly, while summer river levels will have decreased [44].

Extreme precipitation events will likely increase during some seasons and in some areas of the province [5,41,70,72]. Heavy precipitation events in BC include phenomena known as ‘atmospheric rivers’ where highly concentrated water vapour streams move moisture from tropical regions towards the poles. These occur frequently in the fall and winter in BC, and impact coastal areas with periods of intense precipitation and flood events [41,70,74]. More frequent atmospheric river events after 2040 (approximately double the current number per year) will affect ecosystems along the coast [74].

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