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000789 MOUNT BACHELOR, OREGONo-Under the dome of a concrete-gray sky, Stan Fox assembles four pieces of aluminum tubing into a 3- meter-long hollow pipe. After standing it on end, he plunges it through more than 2 me- ters of snow at Dutchman Flat, an alpine meadow perched on the shoulder of this 3000-meter mountain. Fox, who heads the Oregon snow-survey program for the U.S. Department of Agriculture's Natural Re- sources Conservation Service (NRCS), re- moves the .tube and reads the snowpack depth, a measurement that has been tracked at nearby sites monthly since the 1930s. To- day the snow is 250 centimeters deep, and by comparing the weights of the tube both filled and empty, Fox and a colleague deter- mine that the snow contains about 30% liq- uid water. If all the snow were instantly liq- uefied, the water would be nearly 1 meter deep. Not too bad. In a region prone to spikes in precipitation, Dutchman Flat is more than 15% above its 30-year average. "The snow in these mountains is a virtual reservoir," Fox says. As the snow melts in the spring and summer, it will slowly release that water, filling streams and reservoirs, which provide lifeblood to the region during the normally bone-dry smnmer months. But indications are that this age-old cycle is beginning to change. New assessments of decades' worth of snowpack measurements show that snowpack levels have dropped considerably throughout the American West in response to a 0.80C warming since the 1950s. Even more sobering, new studies re- 1124 veal that if even the most moderate regional wanning predictions over the next 50 years come true, this will reduce western snow- packs by up to 60% in some regions, such as the Cascade Mountains of Oregon and Washington. That in turn is expected to re- duce summertime stream flows by 20% to 50%. "Snow is our water storage in the West," says Philip Mote, a climatologist at the University of Washington (UW), Seattle, who leads a team that has produced much of the new work. "When you remove that much storage, there is simply no way to make up for it." The impacts could be profound. In the parched summer months, less water will likely be available for everything from agri- culture and hydropower production to sus- taining fish habitats. Combined with rising temperatures, the dwindling summertime water could also spell a sharp increase in catastrophic fires in forests throughout the West. With much of the current precipitation headed downstream earlier in the winter and spring, the change is also likely to exacer- bate the risk of floods. For resource managers already struggling to apportion limited water supplies through- out the West, the predictions are grave. "If that's true, it would have a huge impact," says Christopher Furey, a policy analyst with the Bonneville Power Administration in Portland, Oregon, which markets electricity from over a dozen power-generating dams in the Columbia River Basin that provide power to millions of people. In a region where farmers, fishers, recreationalists, and municipalities already compete for water, climate change may be setting the stage for an entirely new round of conflicts. "We think of the water wars in the past," says Fox, referring to the epic battles over rerout- ing western waters in the early 20th century. "In the future they will probably be more peaceful but much more prevalent." Too wet. too soon The root of the problem is easy to state: The semiarid West has too little water, spread too unevenly throughout the year. Most ofMon- tana sees less than 46 centimeters of precipi- tation a year. Even rainy Portland receives only about one-tenth of its annual 91 cen- timeters of precipitation during the summer. For most of California the fraction is even smaller. Philadelphia, by contrast, typically receives 102 centimeters of annual precipita- tion. 30% of which comes in the sununer. Thanks to massive dam-building in the first half of the 20th century, more than 60 million people-roughly one-fifth of the U.S. population----now live in the Pacific and Intermountain West. Those tens of mil- lions of people are dependent not just on water, but on snow. Snowmelt makes up 75% of all water in streams throughout the West. If that snow falls as rain or melts too early, there will be little water left in the virtual reservoir come late summer and fall. Unfortunately, that is just what appears to be happening. Back down the mountain in a conference 20 FEBRUARY 2004 VOL 303 SCIENCE www.sciencemag.org