New report predicts severe climate impacts on Lake Tahoe area

Iconic Lake Tahoe could see its regional snowpack decline by as much as 60 percent over the next century, with increased floods more likely around 2050 and prolonged droughts closer to 2100, according to a new report from scientists who have studied the lake for decades.

The study, written for the U.S. Forest Service's Pacific Southwest Research Station, said the lake and its surrounding region could be headed for something of a winter tourism and water supply disaster over the next century as snowpack melts even under the rosiest scenarios.

The average snowpack in the northern Sierra Nevada mountains that ring the lake on the California-Nevada border will decline by 40 to 60 percent by 2100 "under the most optimistic projections," says the report from three researchers at the University of California, Davis.

Under less optimistic models, the melt-off could be accelerated. By the end of the century, precipitation in the region "could be all rain and no snow," and peak snowmelt in the Upper Truckee River -- which is the largest tributary flowing into Lake Tahoe -- could occur four to six weeks earlier by 2100, the report says.

Such predictions could mean bankruptcy for ski destinations that surround the lake, including the home of the 1960 Winter Olympics, Squaw Valley USA. Squaw Valley and other resorts are an accessible stop for skiers throughout the West and the heavily populated California coast.

Rain and more runoff

"Hydrology output from the downscaled climate modeling suggests a significant reduction in the amount of precipitation falling as snow in the Tahoe basin," the report says. "This could have consequences for water supply as well as winter recreational sports."

More crucially perhaps, the basin -- which is warming faster than the rest of California and Nevada -- is a key source of water for Reno, Nev., and other downstream water users. And the lake's famous clarity, which has recently improved after years of decreased visibility, is likely to reverse and worsen as more runoff finds its way into the lake.


"It is clear that by 2100, the Tahoe Basin will be different from the one we know today," said Robert Coats, a researcher at UC Davis and consulting hydrologist.

Warmer temperatures could also lead to unprecedented runoff, erosion problems and stormwater basins overflowing, though the authors of the report said "best management practices" will be able to accommodate most of the increase, causing only a 10 percent decline in urban stormwater containment.

All that said, the authors of the report went to great lengths to describe their findings as projections that are based on untested computer models.

The report was written by Coats, John Reuter, associate director of the UC Davis Tahoe Environmental Research Center, and Geoff Schladow, the center's director. They said the study drew on 100 years of data in an attempt to describe temperature and precipitation changes that have already started reshaping the Tahoe region.

'First detailed glimpse' of impacts

The data were combined with new computer models to produce detailed local projections out to the year 2100. The researchers used two carbon emission scenarios -- a "business as usual" case followed by an "optimistic" model -- with the latter assuming slower growth in emissions and aggressive curtailment.

"While there is always some uncertainty when projecting this far into the future, the results appear reasonable," Reuter said. "They provide environmental managers and scientists with our first detailed glimpse of the potential impact of climate change."

The intent of the report is to give resource managers a better shot at adapting to reduce the risks of climate change. The authors seemed particularly concerned with the effects of prolonged drought toward the end of the century, which could reduce water levels and cause wildfires in a region already prone to them.

Schladow said the report also highlights the need for Lake Tahoe to restore its water quality in the short term, while the region still has control. The report describes a potential "internal loading of nutrients" that could lead to fundamental change and algal growth.

"Reducing the load of external nutrients entering the lake in the coming decades may be the only possible mitigation measure to reduce the impact of climate change on lake clarity and trophic status," the report says.

Others who collaborated on the report include Goloka Sahoo at UC Davis, Mike Dettinger at the U.S. Geological Survey and Scripps Institution of Oceanography, Brent Wolfe of Northwest Hydraulic Consultants, John Riverson of Tetra Tech Inc., and Mariza Costa-Cabral of Hydrology Futures LLC.

Click here to see the report.

Sullivan reported from San Francisco.

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