Forecast for the West: Less Snow, More Floods

Increases in rainfall threaten to inundate reservoirs—and even fuel forest fires.

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Firefighters work against fast-moving wildfires in the hills of the Santa Clarita Valley, a community an hour's drive north-east of Los Angeles. 10/22/2007

By 2040, scientists predicted yesterday, the Sierras and Colorado Rockies will shed most of their snowpack by the beginning of April each year. With average temperatures rising across the region, more precipitation will fall as rain and less as snow, and what snow does fall will melt earlier than it has in the past.

The consequences could be diverse. Here are a few of the elements:

Water. Rivers, swollen with rain and snowmelt during the winter and spring, will flow at unusually high levels. Unless reservoirs and other water supply infrastructure get updated to expand their capacity, they could become more susceptible to flooding, the researchers say.

Earth. Floods aren't the only threat. Early snowmelt also leads to months of low water flow later in the year, so the soil is more likely to get parched. Limited water supplies could hurt farmers and set up conflicts between agricultural areas, thirsty cities, and ecosystems that depend on brimming rivers and streams.

Fire. Forest fires are also projected to increase in the western United States. As the ground dries out, so does fuel for forest fires, including trees, undergrowth, and dead plant matter. That has already led to more large fires in the western United States, although an expert has told me it was not necessarily behind the major wildfires in Southern California last year.