California snowpack melt stirs water worries

By Leonard Anderson

SAN FRANCISCO (Reuters) - Water content in the Sierra Nevada snowpack in California continues to drop toward its lowest level since 1990, raising concerns about the availability of water for generating hydroelectricity and irrigating the state's vast farmlands.

Longer term, scientists have projected that 25 percent of the California snowpack could disappear by 2050 due to global warming and climate change.

State water officials say reservoir storage levels are at or above normal after a very wet 2006 -- the fifth wettest on record in the northern half of the state -- but warn that two consecutive dry years could trigger water shortages.

California's last major statewide drought was 1987-1992.

A survey showed the snowpack in California was only 46 percent of normal in March, down from 64 percent in February, and the water content fell further to 39 percent on Thursday, according to the state's Department of Water Resources.

A big reduction of the snowpack and earlier snowmelt would require more reservoirs to prevent flooding and ensure reliable water supplies, while higher water temperatures would affect the Delta ecosystem in California's farming heartland, reducing water quality and threatening wildlife, according to DWR.

"A warming climate means more water will fall in the form of rain rather than snow, challenging the capacities of existing water reservoirs in parts of the world reliant on snowmelt," a study of climate change effects by the San Francisco-based Global Business Network consulting company said.

"The Western United States and Central Asia are especially vulnerable to this effect," it said.

In the Pacific Northwest, which relies on hydroelectric power for 65 percent of electricity deliveries, rainfall has been hearty in Washington and British Columbia, boosting water runoff in the past few weeks.

But rains at lower elevations of the Cascades mountains have melted snow that otherwise would have helped boost Columbia River flows later this spring, according to the Northwest River Forecast Center.

California expects to have enough water in storage to meet peak demand for hydroelectricity this summer but a prolonged heat wave could tighten supplies.

"Reservoir levels are way above normal, so we should be okay," said Gregg Fishman, spokesman for the California Independent System Operator, manager of most of the state's transmission grid.

Gov. Arnold Schwarzenegger has proposed a $5.95 billion program to add more surface and groundwater storage in the Central Valley and make other improvements in the state water system.

"With California's booming population, and with the impact that global warming will cause to our snowpacks, we need more infrastructure, a wide-ranging water storage and delivery system, including above-ground facilities," Schwarzenegger said.