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Monday, July 17, 2006 | Each spring, Rick Van Schoik suits up earlier and earlier for his white-water rafting trips.

In search of the most dramatic rides – the frothy rapids that make trips to Yosemite and Idaho worthwhile – Van Schoik copes with icy water and frigid weather. A wetsuit, splash protector and neoprene boots are common. Sometimes, Van Schoik said, he rushes down water that was frozen just a day earlier.

Climate experts point to one reason that Van Schoik, a professor of environmental security at San Diego State University, rafts in 30-degree water early each spring: Global warming.

Scientists say the planet’s slowly warming temperature is already causing snow packs to melt about a week earlier than in the 1950s. By 2050, they say, those melts will happen three weeks earlier. By 2100, they project it will be a full month.

Scientists disagree on many predictions related to global warming. But they agree on this: A warmer world means more precipitation will fall as rain, not snow.

The trend could have serious implications in San Diego – an arid region that gets more than 80 percent of its water supply from rivers fed by melting snow packs in the Sierras and the Rockies.

Scientists’ least-dire warming scenario projects a 1-degree Celsius increase in the world’s average annual temperature by 2050. As that rises, mountainous snow packs will be smaller. Spring-time streams will gurgle to life much sooner, melting at a time when dams and levees can’t store the water because levels are kept low to control flooding.

Instead of a long, steady flow of water through the middle of July, the resulting runoff would come in a shorter, faster burst. The snow melt, which is normally stored to supply water for drinking and agriculture, would simply be lost. A new state report says California could lose 1.6 trillion gallons of water each year. That’s 10 times more water than San Diego County residents used in 2005.

“California agriculture should be scared to death,” Van Schoik said. “California insurers should be scared to death. The firefighters should be scared to death. I don’t mean it’s going to happen this summer, but climatologists and scientists know it’s going to happen this century.”

The unanswered question for scientists is whether rainfall will increase here and offset the lost snowmelt. A few climate models predict California will see a boost in rain from an El Nino-fed pattern. But a majority of models agree that two regions of the world will get drier: the northern Mediterranean and the American Southwest.

If that happens, it could expand the globe’s belt of deserts, said Michael Dettinger, a U.S. Geological Survey research hydrologist. That dry belt stretches around the globe from the Sahara to the Australian outback to desolate stretches of Mexico. It could expand north, Dettinger said.

“We’re sitting on the edge of it, with Mexico being the middle of it in North America,” Dettinger said. “That’s probably not good news for us in San Diego.”

The area has already felt the effects of earlier snowmelt, according to a Scripps Institution of Oceanography research team. In a recently released report, they pointed to global warming – not fire-suppression policies – as the reason for an increase in major Western wildfires. An earlier snowmelt, their report said, brings an earlier and longer fire season.

As snow melts earlier, water shortages will become more frequent and more pronounced, said Tim Barnett, a Scripps marine physicist and climate specialist. He did not contribute to the report.

“You won’t wake up one morning and say: ‘Global warming is here,’” Barnett said. “It’ll be a slow, aggravating death of 1,000 cuts.”

Barnett paints a dreary picture of the future when he describes draconian measures he imagines may one day be used to reduce water consumption – perhaps as soon as 2020. No swimming pools. No green lawns. Water police.

“I believe the environment will eat it first,” Barnett said. “Do you want to go thirsty or kill off the last salmon in the Sacramento River?”

Some scientists point to the current long-term Southwestern drought as a possible preview of a warmer age. Lake Mead’s water level is steadily dropping. As it has declined, the Hoover Dam’s hydroelectric production capacity has waned, too. The massive Nevada dam has lost almost a small power plant’s worth of energy capacity.

If the lake drops another 80 feet, the dam’s turbines will be shut off, closing a facility that provides electricity to 1.3 million people. The lake’s elevation is expected to drop about 20 feet by May.

Water providers throughout the west are beginning to consider the long-term effects of more frequent droughts prompted by global climate change.

In a report released last week, the state Department of Water Resources said deliveries from the State Water Project, a major source of San Diego’s water, could drop 10 percent under one scenario. A best-case scenario projects its reserves boosted by one percent.

“We’re in the early stages of understanding what the implications are going to be statewide and regionally,” said Sue Sims, a water resources department spokeswoman. “We know it’s coming, it’s just a matter of what we need to be doing.”

The Bureau of Reclamation, the federal agency that manages water use of the Colorado River, aims to have a plan in place by the end of 2007 to determine who gets water if climate change prompts a long-term shortage, spokeswoman Colleen Dwyer said. The bureau, which supplies water to 31 million people, has never reduced its supplies to users.

SDSU’s Van Schoik said climate projections should shake the nerves of the San Diego County Water Authority, which distributes water to three million residents locally.

Barnett concurred: “What scares the hell out of me is that San Diego has no control over its water – it’s the Metropolitan Water District. Doesn’t that make you a bit nervous if someone else is holding the keys to your water supply?”

The Los Angeles-based MWD, which provides nearly 80 percent of San Diego’s water, isn’t specifically addressing climate change in its long-term plans, spokesman Bob Muir said, though it is developing projects to increase storage.

County water authority spokesman Bill Jacoby acknowledged a “real challenge” posed by climate change, but said the agency is establishing emergency reserves and a more diverse water supply.

“What we’ve seen is that there will probably be some changes in the type of precipitation and how much we get,” Jacoby said. “It’s not quite clear what all of that means. The best thing we can do is build our local supply and build local reserves.”

Not everyone is concerned about the potential effects of the earth’s warming. Eric Larson, executive director of the San Diego County Farm Bureau, said the farming community isn’t yet talking about the long-term effects that water shortages could have on agriculture.

“We’re not scientists,” he said. “We’re somewhat on the sidelines right now, watching the debate. That’s about as much as I can say we’re doing right now.”

Please contact Rob Davis directly with your thoughts, ideas, personal stories or tips. Or send a letter to the editor.

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