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Nearly half of the Fraser River basin will have gone through a transition from snow-dominated to rain-dominated by the end of this century in response to global warming, two University of Northern B.C. professors are predicting.

Dr. Stephen Déry and Dr. Siraj Ul Islam base their outlook on a model of the basin’s hydrology. They ran the model for 150 years, from 1950-2099, using future climate projections from 21 global climate models.

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As the climate warms, the ratio of snow to rain will decline, causing river flows to peak earlier in the year with reduced volume, according to their projection. As well, they say run-off in the cold seasons — fall and winter — at the outlets of the Fraser River and its major tributaries will increase substantially and its year-to-year variability will more than double.

Photo by DARRYL DYCK / THE CANADIAN PRESS

The marked increase in cold-season run-off is most likely linked to heavy rainfall from more frequent land-falling “atmospheric rivers” — long, meandering plumes of water vapour often originating in the tropical oceans that bring sustained, heavy precipitation to the west coasts of North America and northern Europe, often known as Pineapple Express storms.