California: Global warming to affect water supply -
More rainfall means smaller Sierra snowpack
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Source: SF Chronicle
Global warming to affect water supply
More rainfall means smaller Sierra snowpack
David Perlman, Chronicle Science Editor
Friday, June 15, 2001
California water planners face a problem they never thought they'd encounter: global warming is hitting the High Sierra snowpack. And just how the planners cope with it could affect every city-dweller, every farmer and every water-using industry in the state for years to come.
Scientists are in broad agreement that the world's climate is steadily warming -- whether due to "greenhouse gas" emissions from industry and automobiles, or to natural variability. And there is evidence that it is already altering the annual ebb and flow of the state's water supplies.
It's a matter of "more rain, less snow," says Dan Cayan, director of the climate research division at the Scripps Institution of Oceanography in La Jolla (San Diego County). And that's bad, he says, because California's water supply largely depends on the winter snowpack in the high mountains that must feed the state's lowlands the rest of the year.
A major change is already evident in the decreasing depths of the mountain snows that pile up each winter, in the unseasonal winter rainfalls that drench the mountains instead of snow, and in the speed of the snowmelt during spring.
Total precipitation over California hasn't changed significantly on average over the years, but seasonal variations between rain and snow show that a significant warming trend is under way, according to Cayan.
Annual surveys of mountain snow depths and water levels of California's major rivers show that before the 1960s runoff in the late spring and early summer amounted to a good 40 percent of the total runoff each year, Cayan said.
But since the mid-1970s, runoff during the late spring and early summer has dropped to barely 30 percent of the annual total, he said.
Peter Glieck, a hydrologist and climate specialist who heads the Oakland- based Pacific Institute for Studies in Development, Environment and Security, a nonprofit research organization, has tracked California's changing climate record for many years. He says his findings add powerful evidence that the warming trend is real.
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"The problem of managing the state's water resources more rationally in view of the changing climate is urgent now," Glieck says. "We need detailed studies to decide what to do. Studies are a lot cheaper than floods."
Officials of the California Department of Water Resources are starting to look at the effects of climate change as they develop the 2003 California Water Plan that state law requires the department to produce every five years.
"I can look at the Sierra summit right now, and there's no snowpack at all up there, while the major reservoirs downstream are full," said Jonas Minton, deputy director of the California Department of Water Resources, speaking from his office in a Sacramento office tower. "The warming problem is just beginning, but it's certainly focusing our attention."
As Minton sees it, the warming trend poses at least three increasing dangers:
-- Severe lowland flooding as rains in the winter replace mountain snowfalls;
-- Rising sea levels that reach into the Sacramento-San Joaquin River Delta and threaten century-old levees that must protect the rich croplands;
-- The intrusion of salt into Delta waterways that disturbs both fisheries and the natural delta ecology on which farmlands depend.
How the Department of Water Resources hedges against these changes are what Minton and the department's experts must contend with over the next two years as they develop the state water plan.
The last such document in 1998 included forecasts for the state's water supply and demand over the coming 20 years, and provided recommendations for dam building, flood control, water management and conservation measures. Now, the department is gearing up to draft the plan for 2003.
On Wednesday in Los Angeles, Cayan, Glieck and other experts will offer the department's 60-member advisory committee the latest evidence that the warming problem could grow steadily worse.
The Water Department has a 60-member advisory committee made up of "stakeholders" -- the people most affected by water policies like agricultural water districts, urban water departments, food processing industries and public utilities. All provide input for the state's water planners. The committee meets every two months or so for the next two years until the final plan is released.
E-mail David Perlman at [email protected].
California Department of Water Resources
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