'Currently scheduled depletions are simply not sustainable,' scientists warn

By DAVE WILKINS

Capital Press

While skeptics continue to challenge the notion of human-caused global warming, scientists have begun to assess its potential impacts on the West's water supplies.

In a report released last year, researchers at the University of California-Davis projected that a lack of water brought on by climate change would result in reductions in irrigated crop acres and the loss of farmland in the Central Valley.

Reduced water availability and lower crop yields could result in gross revenue losses of up to $3 billion by the year 2050, the researchers estimated.

California farmers have more immediate water concerns -- most of them linked to the Endangered Species Act and the Delta smelt. Court-ordered restrictions on irrigation deliveries have already resulted in more than 500,000 acres of farmland in the San Joaquin Valley being temporarily idled.

Water will remain a major concern even if solutions are found to fish survival, researchers say.

In 2008, scientists Tim Barnett and David Pierce of the Scripps Institution of Oceanography at UC-San Diego released a report predicting a 50 percent chance that Lake Mead will run dry by 2021 if climate change occurs as expected and water use isn't curtailed.

Water from Lake Mead flows down the Colorado River and through a system of aqueducts to Los Angeles, San Diego and other communities in the Southwest. The system has been running far below capacity in recent years because of drought.

"When expected changes due to global warming are included as well, currently scheduled depletions are simply not sustainable," Barnett and Pierce wrote in their paper, "When will Lake Mead go dry?"

They noted that several other recent studies have estimated that climate change will lead to reductions in runoff to the Colorado River system. Those studies consistently forecast runoff reductions of between 10 and 30 percent over the next 30 to 50 years.

In November 2008, the U.S. Bureau of Reclamation released a report outlining the potential effects of climate change on the operation of the Boise River reservoir system in Western Idaho. The most significant impact will be an increase in flooding along the Boise River during January through March, the agency concluded.

Runoff that arrives too early for agricultural diversion may be stored, leading to a reduction in diverters' reliance on natural flow and an increase in reliance on stored water, the study found.

However, that conclusion is built on the assumption that diverters will behave as they have historically, "and little research has been performed to quantify how agricultural diversions will be altered by climate change," authors of the report said.

More information is required to understand how irrigators would actually respond to climate change, they said.

Preliminary indications suggest that climate change will lead to an increase in dryland farming, changes in cropping patterns and timing of water diversions, the report found.

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