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state's agriculture economy would be meas- ured in the billions of dollars. What is more, Fisher says, because ac- cess to irrigation water in California de- pends on the historical system of first-come, first-served water rights, those losses will likely be absorbed primarily by the farmers lowest on the water-rights totem pole, driv- ing many out of business. That same pattern is likely to hold true in the Northwest, par- ticularly in the dry lands east of the Cas- cades. "It's not going to be feasible to have the irrigated acreage we have now," Mote says-fighting words in a region long wed- ded to an agricultural way oflife. Forests are also likely to suffer, accord- ing to Anthony WesterIing, a climate re- searcher at Scripps. Westerling recently fed data from Cayan and Knowles's climate and hydrology models of the Sierras into a model of his own that attempts to forecast changes in wildfires. WesterIing says his preliminary results show that fire danger will soar. "The mean area burned more than doubled by 2090" relative to the present, Westerling says. Although less easily quantified, low sum- mertime stream flows are also expected to exacerbate problems with declining. fish runs, crimp water supplies for recreation and cities, and increase the likelihood of winter and springtime flooding throughout the Northwest and Califomia. But not all the im- pacts are sure to be bad. Last year, John Fazio, a river flow an- alyst with the Northwest Power and Conservation Council in Portland, plugged some of the UWgroup's hydrology forecasts into his Columbia River flow models and found that a warmer Northwest may actually benefit Northwest electricity consumers. Warmer winters, Fazio says, will likely lower the need for electric- ity during the region's peak de- mand period, and an expected small increase in wintertime pre- cipitation could churn generators ~ to the tune of an extra 1900 megawatts of ~ power-nearly enough to power two cities ~ the size of Seattle. Of course, if precipitation ~ swings toward the dry side, it could wind up ~ costing rate payers hundreds of millions of ~ dollars, he says. ~ No matter how the climate evolves, water '3 ~ managers will face uncomfortable tradeoffs ~ between providing water for agriculture, hy- a dropower, and recreation, and keeping it in : streams to support fish runs. In their current ~ Climatic Change paper, for ef{ample, Letten- g maier and colleagues show that to keep sum- ~ mertime flow levels in the Columbia River ~ high enough to support endangered-fish re- u covery plans, water managers will likely 000792 have to sacrifice 10% to 20% of the river's wintertime hydropower generating capacity, because it will force water managers to draw down their reservoirs in the summer. "Even with these reductions in power, late-summer minimum flows would still be lower than at present," the authors write. More big dams? In a region prone to water shortages, talk of such tradeoffs doesn't go down easy. "We already have a problem with shortages," says Maury Roos, chief hydrologist for the state of California. And coming up with the water to deal with population growth throughout the region is already an acute problem, he adds. ''This will certainly make the problem worse." In hopes of head- ing off some of those problems, Roos and other water officials are beginning to in- corporate climate change into their re- gional water plans. California's latest draft water plan, for example, discusses climate change, al- though it doesn't yet recommend changing California's infra- structure. Portland, Seattle, and other cities have begun studying the issue in detail to see whether they need to change their water- management plans. Initial rumblings are also being heard among advocates for building new dams throughout the West. That comes as some- thing of a surprise to many, because during the Clinton Administration, then-Secretary of the Interior Bruce Babbitt claimed that the era of big dam building was over, due to their adverse impacts on fish and wildlife. Already, for example, California is considering building several new dams as part of a joint state and federal effort to provide water for threatened ecosystems NEWS Focus while keeping water available for farmers. Washington too is flirting with building a dam at a cost of more than $ I billion in the eastern part of the state to provide irriga- tion water for farmers near Yakima. And Idaho water managers say that climate change may force them to build new reser- voirs to prevent winter floods along the Boise River, where one-third of the state's inhabitants currently live. But due to their high dollar and environ- mental costs, many water experts doubt whether such projects will go forward. "Dams are tough fights and so expensive," says Hal Anderson, planning chief for the Idaho Department of Water Resources. And even jf built, they will only soften the blow. Dangerous consequences. Over the next cen- tury, larger winter and spring runoffs from melting snow are expected to increase flood- ing and catastrophic wildfires. With the amount of spring snow expected to be lost due to climate change, ''there is no way we're going to build that many dams to capture it all," Mote says. Other strategies may help. Most water officials agree that there is much that can be done to conserve water, particularly by lin- ing irrigation canals and making other im- provements to irrigation. As well, a handful of new programs have sprung up recently to buy or lease water rights from fanners and then keep the water in stream during the low-flow months to improve habitat for fish. Last year, for example, one umbrella effort called the Columbia Basin Water Transac- tions Program sponsored 32 such deals to keep 28.4 million cubic meters of water in tributaries where it's needed most. That amount of water pales in comparison to what stands to be lost. But for now, water planners still have some time to act before climate change alters the American West in a way humans have never witnessed. -ROBERT F. SElMa www.sciencemag.org SCIENCE VOL 303 20 FEBRUARY 2004 1127