Climate models predict that as global temperatures rise over the next seven decades, subtropical regions like the American Southwest will get drier, while more northern areas, including much of Canada, will get wetter. But for the rest of North America the 2080 water forecast is mixed. The Northeast and the Pacific Northwest may see only a slight increase in annual precipitation, maybe one or two percent, but storms are likely to become more intense. Seasonal variation is likely to increase as well, leading to wetter winters and drier summers that could disrupt local water supplies.
People living near the Cascades will be among the first to see a difference. They rely on melting mountain snowpack for their water in the parched summer months. “The snow acts like a water tower, storing water in the winter and then delivering it in the summer,” says University of Washington hydrologist Alan Hamlet. As the planet heats up, much of that snow may fall as rain instead. “The Cascades could see a 50 percent loss of snowpack, which could translate into a large reduction in summer water,” says Hamlet.
In the Northeast, too, the water supply may undergo drastic changes even as total precipitation stays about the same. A warmer atmosphere will hold more moisture, unleashing intense but less frequent rainstorms. Droughts could become more common, but so could storms like Hurricane Irene, which caused record flooding in the region this August. “Water suppliers should be thinking hard about managing these extremes,” says water resources engineer Casey Brown of the University of Massachusetts at Amherst. “It will only get worse.”