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Monday, April 30, 2007 | San Diego’s two largest water sources — the Colorado River and the Sierra Nevada range — are at their lowest levels in decades, raising concerns that the arid region may face water shortages as soon as next year.
The Colorado River is enduring its eighth year of drought, and the winter snow that blanketed the Sierras contains just 40 percent of the water content it typically does. San Diego County relied on the two sources for 78 percent of its fresh drinking water last year. The region, in recent years, has had to import up to 95 percent of its water a year from those two sources.
The prolonged drought on the Colorado — the worst in a century — is not news to water agencies. But the state Department of Water Resources is now reporting that the water stored in the Sierras is at its lowest level since 1988. If next year’s winter is similarly dry, water shortages could follow.
The Sierra Nevada range serves as a large reservoir of California’s drinking water. But less snow fell across the Sierras this winter, said Arthur Hinojosa, chief of the hydrology branch in the state Department of Water Resources’ flood management division. And what little snow did fall melted earlier, at a time when flooding concerns prevented dams and reservoirs from catching it.
“Usually one year is not an issue in this state,” Hinojosa said. “So many regions are built to handle it. The southern water agencies have lots of storage. They can weather a dry year. [But they] would be hard-pressed to survive two years like this, especially with the Colorado on short supply.”
Southern California’s water supply is designed to be diverse, relying on two mountain ranges separated by hundreds of miles. Even though the Colorado River has run low, the Sierras have been more reliable. Until this year.
“It is a double whammy,” Hinojosa said. “The Colorado system is still suffering. To have two of the big imported supplies running on the dry side is reason enough to be cautious with conservation plans.”
The reservoirs fed by Sierra snowmelt are now full, which will provide a stable water supply through this year, Hinojosa said. Neither the state Department of Water Resources nor the Los Angeles-based Metropolitan Water District have trimmed their water allotments. The San Diego County Water Authority receives most of its water from the district.
But as a precaution, wide-reaching requests for voluntary water conservation should be expected this summer, said John Liarakos, a water authority spokesman.
Adding to the problem, an Alameda County Superior Court judge has ruled that water cannot be pumped south from Northern California reservoirs, until the state receives proper permits to kill the endangered fish that the pumps trap and grind up. While a brief shutdown wouldn’t affect San Diego’s water supply, a long-term closure could force the Metropolitan Water District to draw down its reserves — a potentially valuable water source if the Sierras and Colorado River continue running low.
“We’re kind of in the perfect storm here,” Liarakos said. Asked whether the situation is as dire as the drought that hit San Diego between 1987-1992, he answered: “It is on par. Some are saying it’s more severe.”
Drought is not an unusual phenomenon in California, but it is a significant policy-shaping force. The legendary 1987-1992 drought brought severe water shortages. In 1991, the Metropolitan Water District cut its water delivery to San Diego by 31 percent and threatened a 50 percent reduction. The calamity helped reform the way Californians considered their water reliability, just as the 2000-2001 energy crisis similarly reshaped the electricity industry.
In the years since, cities throughout California have begun considering desalination plants as drought-proof water supplies. The water authority diversified its supplies and launched conservation efforts, though 78 percent of the San Diego County’s water still came from the Sierra Nevada and Colorado River last year.
Widespread drought simultaneously striking the Sierra Nevada range and Colorado basin is not unprecedented, said Dan Cayan, director of the Climate Research Division at Scripps Institution of Oceanography.
“There’s more than a random chance that when we get drought in the Southwest it tends to have a broad footprint,” Cayan said, “so it covers part of the Sierras and a good part of the Colorado basin at the same time.”
The threat of those infrequent but far-reaching droughts highlights our water reliability’s precariousness, as well as the stress that residential development is putting on the Colorado River. The federal Bureau of Reclamation, which manages the Colorado and supplies water to 20 million people in the lower river basin — Southern California, Nevada and Arizona — boasts that it has never declared a shortage. Today it is developing contingency plans for water deficiencies.
Rampant development in desert metropolises such as Las Vegas and Phoenix is taxing a water supply once considered inexhaustible. At the same time, the upper Colorado basin — states such as Colorado, Wyoming and Utah — is rapidly growing and using more of the water it is entitled to. The southern states have historically relied on that excess water.
“At some point in the future, the extra water we used to get from the upper basin into the lower basin isn’t going to be available,” said Bob Walsh, a Bureau of Reclamation spokesman. “Even without a drought there may not be as much water as there has historically been.”
Eight years ago, the Colorado River was so full the bureau was drafting guidelines to address surpluses. Today, it is contemplating the opposite — how to address shortages. The river is expected this year to get 70 percent of the snowmelt it typically receives. Lake Mead, the massive Colorado River reservoir formed by the Hoover Dam, is at its lowest level since 1965.
But Colorado River shortages don’t appear imminent. While Lake Mead and Lake Powell are at half-capacity, they still have massive amounts of water stored, giving at least a two-year cushion before shortages are declared, said Michael Cohen, senior associate at the Pacific Institute, an Oakland-based think tank.
“San Diego and California in general have pretty senior rights to the Colorado River,” Cohen said. “There can be shortages on the Colorado for years and California would continue to receive its rights, while Phoenix and Central Arizona takes the largest hit.”
The threat of climate change also complicates the future of our water supply, though scientists are quick to point out that there’s no provable connection between the current situation and human-fueled climate change.
“There are a lot of things we don’t understand — and one is the decadal swings of climate,” said Brad Udall, director of the Western Water Assessment at the University of Colorado. “In the long run, in the 25- to 50-year timeframe, it’s got to get drier if you believe these [climate] models.”
Simultaneous drought in the Sierras and Colorado basin “may be unlucky,” Udall said. “On the other hand it may be the future.”
In a warmer world, more snow is expected to fall as rain, while spring melts are projected to begin earlier, at a time when reservoirs must be kept low for flood control. The unanswered question for scientists is whether rainfall will increase and offset the lost snowmelt.
“I think the lesson here is that drought is a part of our climate, regardless of climate change,” said Dan Cayan, the Scripps researcher. “Climate change could exacerbate it. The warmer world that’s developing will make water demand by humans and plants and ecosystems even more intense. But drought is part of the climate, and we should expect that we’re going to see it now and again.”