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State to consider climate change in forecasting water supplies

LOS ANGELES (AP) – State water officials, faced with predictions that the Sierra snowpack could shrink drastically in coming decades, will consider including climate change in California’s long-range water forecast.

It would be the first time the effects of global warming became part of the California Water Plan. Officials working on an update to the document will discuss the issue today in Los Angeles.

Any reduction of the winter snowpack – which now covers on average 13,000 square miles early each spring – would weigh heavily on California, which depends on it for half the water required for agricultural, industrial and residential use.



Rising temperatures could remove the snowpack from two-thirds of the Sierra Nevada and other major California mountain ranges by 2060, said Michael Dettinger, a research hydrologist with the Scripps Institution of Oceanography and the U.S. Geological Survey.

”By the time our kids are looking at retirement, the snowpack over a large part of the Sierra would effectively be removed,” he said.




A jump of 2 to 4 degrees Celsius, which scientists generally believe is likely over the next half century, could leave overall precipitation levels unchanged in California. But how that precipitation falls, especially during winter, would change dramatically, skewing the delicate balance of the state’s hydrological system.

Modeling done by Scripps scientists shows rain would become the main form of winter precipitation in the Sierra.

While the water dumped by a winter rain storm runs off comparatively quickly, snow piles up, only to melt much later in the season when temperatures and the state’s thirst for water rise.

”It’s a particularly nice reservoir, the Sierra Nevada is, because it accumulates water in the form of snow and then slowly releases it through the year,” said Jonas Minton, deputy director of California’s Department of Water Resources.

Should more rain fall, it would boost the state’s water supply at a time when demand is lowest but the risk of flooding is highest.

That would force California to allow more runoff to flow directly to the Pacific Ocean so its reservoirs could accommodate any surge from increased rainfall later.

”It’s a double whammy: You’re left needing more reservoir space in the winter to handle the increased supply, but you have less runoff in the dry season to recharge them,” said Noah Knowles, a postgraduate researcher at Scripps.

State officials have taken note of the predictions and likely will include them in the 2003 California Water Plan, a document updated every five years.

”My estimate is for every degree Celsius increase, you’re lifting the snow level 500 feet. With 3 degrees, you’ve lifted it 1,500 feet,” said Maurice Roos, the state’s chief hydrologist. ”For a 1,500 feet movement of the snow line, you would lose one-third of the April to July runoff, even with the same amount of precipitation.”

Despite such dire forecasts, how global warming will affect California is not a given, said William Patzert, a research oceanographer at the National Aeronautics and Space Administration’s Jet Propulsion Laboratory.

”That’s one scenario, but be careful you don’t say more than you know,” said Patzert. ”Mother Nature, just when you think you’ve got her figured out, will come back and bite you.”

Water experts say one answer to any loss of the state’s snowpack would be to compensate with increased artificial storage. But many of the logical spots for dams already have been taken in California, which already strains to store less water than it typically needs in a year, Roos said.

In contrast, the Colorado River system and its network of huge dams can store four years’ worth of demand.


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