The Heat Is Online

Small Warming Could Jeopardize Water Supplies


BOULDER, Colorado, December 20, 2001 (ENS) - Just one or two degrees of global warming could have dramatic impacts on water resources across western North America, a new study suggests.

Teams who have modeled the climate in the area are warning of reduced snowpacks and more intense flooding as temperatures rise.

The research marks the first time that global climate modelers have worked with teams running detailed regional models of snowfall, rain and stream flows to predict what warming will do to the area. The researchers, from the National Center for Atmospheric Research and elsewhere, were surprised by the size of the effect generated by only a small rise in temperature.

Assuming current levels of pollution emissions, greenhouse gases will warm the west coast of North America by just one or two degrees Celsius over the next century, and average precipitation will not change much. But in the model, warmer winters raised the snowline, reducing mountain snowpacks, the researchers told the American Geophysical Union in San Francisco last week.

"We realized that huge areas of the snowpack in the Sierra went down to 15 per cent of today's values," said Michael Dettinger, a research hydrologist at the Scripps Institution of Oceanography in La Jolla, California. "That caught everyone's attention."

The researchers also predict that by the middle of the century, melting snow will cause streams to reach their annual peak flow up to a month earlier. With warm rains melting snow or drenching already saturated ground, the risk of extreme floods will rise.

"We have to believe in these very warm, very wet storms," said Andrew Wood, a water resources modeler at the University of Washington in Seattle.

Since dams can not be filled until the risk of flooding is past, the models predict they will trap just 70 to 85 percent as much runoff as they do now. This is a particular problem for California, where agriculture, industry, a burgeoning population and environmental needs already clash over limited water supplies.

Observations back up the models. Minton points out that an increasing percentage of California's precipitation over recent decades is falling as rain rather than snow.

Iris Stewart, a climate researcher at the University of California, San Diego, has found that in the last 50 years, runoff peaks in the western U.S. and Canada have been happening earlier and earlier. The cause seems to be a region wide trend towards warmer winters and springs.

The research appears in the December 22 issue of the British journal "New Scientist."