August 3, 2008

Yosemite Weather May Become More Severe

YOSEMITE NATIONAL PARK, Calif. _ Scientists predict that climate change will mean more rainfall and less snow in Yosemite in the next 50 years. If that happens, they say, one of the nation's premier outdoor destinations could experience problems _ including severe floods in winter and spring, plus dry wells in the summer.

Farmers in the San Joaquin Valley also could be hurt because reservoirs might not be able to handle large winter runoffs, and water needed for irrigation or groundwater recharge would wind up in the Pacific Ocean.

One of the keys to understanding the future is locked in the traces of minerals and salts contained in water flowing through Yosemite Valley today.

So researchers from the University of California at Merced are collecting data to build an information base with which to compare future research on climate change.

"You can tell the history of the environment from what's in the water," said Dannique Aalbu, a 23-year-old student at UC Merced and one of the researchers.

As she made her rounds of Yosemite Valley in a white Chevrolet Cavalier recently, Aalbu looked like a tourist except for her small bag of equipment. Her stops include Bridalveil Falls, Lower Yosemite Falls, Tenaya Creek and several spots on the Merced River and the streams that feed it.

Aalbu opened the bag near a stream close to the river's Happy Isles Bridge and tossed a probe into the trickling water. A passing tourist wearing a red visor and holding a child's hand talked of scaring off bears with pots and pans, and didn't appear to notice Aalbu.

The probe sent data measuring the water's ability to conduct electricity to her gray hand-held meter. The reading would help researchers know how much of the river water came from snowmelt and how much came from groundwater that had been stored in the soil and fractured bedrock before draining into the river system. Groundwater has more dissolved minerals and salts and is better able to conduct electricity.

Researchers expect that global warming will increase the proportion of the river originating from groundwater.

Yosemite is a good place to conduct research because its watershed hasn't been altered by logging or mining, scientists say.

Overall precipitation in the central Sierra that encompasses Yosemite hasn't changed significantly over the past 50 years. But its form is expected to change between 4,900 feet and 8,200 feet _ which is 70 percent of the park, said Yosemite hydrologist Jim Roche.

If more falls as rain, the mountains' natural role as a reservoir would be disrupted. Snow typically covers the mountains for months and gradually melts, flowing to the dry flatlands as spring and summer temperatures increase. Rain, on the other hand, flows off quickly into rivers. And when it falls atop the snow pack, there is potential for trouble.

With global warming, "the magnitude and frequency of floodings may increase because springtime flooding is usually caused by rain on snow," Fengjing Liu, a research scientist at UC Merced, said in an e-mail.

Flooding could be of the magnitude of the crippling January 1997 deluge, which caused more than $178 million of damage in Yosemite, Roche said.

Slowly-melting snow offers another environmental advantage, Roche said. It's able to infiltrate the soil and build up groundwater supplies that feed wells in the mountains year-round as well as creeks, streams and rivers in the late summer and fall.

Yosemite Valley gets most of its water from wells and its meadows and wetlands also depend on groundwater for their vitality, Roche said.

Could wells start drying up in Yosemite Valley? "It's certainly a possibility," Roche said, adding that mandatory conservation might be necessary, as happened last summer at campgrounds and the hotel at Wawona in the south end of the park.

In a worst-case scenario, visits to Yosemite could be limited, he said: "But that's a long way down the road. We have a lot to learn in the interim to plan for that."

San Joaquin Valley farmers saw the worst happen during the early snowmelt in 1997, said Randy McFarland, a consultant with the Kings River Water Association and Friant Water Authority.

So much water gushed into Millerton Lake so quickly that reservoir managers had to release flood waters from Friant Dam, and much of it flowed down the San Joaquin River to the ocean, McFarland said.

Farmers and water managers believe new reservoirs should be built to help capture high runoffs and store them for dry years, McFarland said.

Others oppose such construction. "The No. 1 priority should be conservation," said Walter A. Shubin, a Kerman farmer.

On one point, however, the researchers, farmers and environmentalists agree.

"Water is more precious than gold, oil or gas," Shubin said. "You can't live without it."


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