By Patrick O'Driscoll, USA TODAY
DENVER The fast-growing states of the arid Southwest must plan for more severe droughts because of a regional warming trend that shows no signs of dissipating, says a new assessment of the Colorado River's water supply.
The report released Wednesday by the National Research Council says agriculture, which uses 80% of the West's water, is the likeliest target for shifting water supplies to growing urban areas. But the council, an agency of the National Academy of Sciences, cautions that "the availability of agricultural water is finite."
Rising population "will inevitably result in increasingly costly, controversial and unavoidable trade-off choices" in sharing the Southwest's most precious natural resource, the report says.
The Colorado River Basin includes seven states: parts of California, the nation's biggest farm producer; Wyoming, and five of the 12 fastest-growing states: Nevada, Arizona, Colorado, Utah and New Mexico.
Until now, water needs have been met by selling or leasing water rights from farms to cities. As population growth demands more of a shrinking water supply, battles could erupt over dwindling farm land and rural landscapes drying up. Some farm production might have to shift elsewhere because of urban growth.
The report says climate reconstructions using tree-ring data and projections with computer models show extended droughts were common in the past and will be longer, more severe and more frequent in the future. "That's not a happy picture," says Ernest Smerdon, a former University of Arizona engineering dean and one of the report's authors.
"The preponderance of scientific evidence suggests that warmer future temperatures will reduce future Colorado River stream flow and water supplies," the report says. Technological measures such as water conservation, de-salting plants and underground storage can help but are not a long-term "panacea for coping" with less water and more people.
"If people think they can save enough water to meet all the future demands, our judgment (is) that it's not going to be that easy," Smerdon says. "(We) are not predicting doom. We are just saying that there are critical issues to be addressed."
The panel does not recommend specific steps except a regionwide study by federal agencies and the states of urban water use. An issue certain to arise is how much agricultural water could be shifted to cities. The report says farm water may be "the most important, and perhaps final, large reservoir of available water for urban use in the arid U.S. West."
Smerdon says the report aims "in plain language" to emphasize the need to act.
The states share the Colorado River under a compact adopted in 1922, an extraordinarily wet period of mountain snows and plentiful river flows. In drier decades since, demand has exceeded supply. A drought since 2000 has shrunk some reservoirs to 50% or less of normal.