Mountain News: Tahoe gets dumped on, but there will be far less by 2100 

click to enlarge UNSPLASH

TRUCKEE, Calif.—Ski resorts of the Tahoe-Truckee area of the Sierra Nevada have been getting the kind of dumps for which they’ve long been known. One recent storm alone delivered more than 1.8 metres of snow, with another such storm over the weekend predicted to deliver 1.5 to two metres to areas above 2,134 metres.

Oh so different from the drought of recent years, when it was possible to walk into meadows in ordinary street shoes to record the snow depths.

It’s also likely to be different again in the future. Not because of drought. But because the warming climate will produce less snow.

That was the conclusion of a study released by the Department of Energy’s Lawrence Berkeley National Laboratory in November. The study, published in Geophysical Research Letters, predicted a 79 per cent drop in peak snowpack water volume by 2100 in headwaters for 10 major reservoirs in California.

Alan Rhoades, a Berkeley Lab post-doctoral fellow and lead author of the study, said a community of models was analyzed. The models tend to disagree about mid-century climatic conditions. By 2100, they cohere that a dramatic decline in the snowpack of the Sierra Nevada will occur if greenhouse gas emissions continue to increase as they have. Carbon dioxide levels last year reached 410 parts per million. Researchers talked to water managers in advance about what metrics would be most useful for resource planning.

“Water managers are constantly competing between how much flood risk can they handle with reservoir storage and how much supply they can provide for urban and agricultural users,” Rhoades said.

California, like Colorado and most other Western states, depends to a great extent upon its mountain snowpack for water. That snow arrives in a very narrow window. “We basically get 50 per cent of our annual precipitation in five to 15 days, or one to two weeks,” Rhoades said in a press release from Berkley Lab issued in December. California’s storms, perhaps unlike those of the Rocky Mountains, tend toward relative warmth.

“So as the world continues to warm, these storms will get even warmer and won’t readily get to freezing, whereby you could have snowfall or snow accumulation and the persistence of snow on the surface,” he said.

The study also found that peak snowpacks will occur, on average, four weeks earlier.

Declines will not be equal across the Sierra Nevada, however. Lower elevations, such as in the Tahoe-Truckee area, will see more rain, less snow. Lake Tahoe when full has an elevation of 1.900 metres. This compares with Colorado resorts, where most base areas are at 2,440 metres to 2,740 metres, with several ski areas topping out above3,660 metres.

The study also found that snow season—both the accumulating time and the melting—will decrease by 20 days by mid-century and by 30 days by century’s end. Is there any way around this? Reducing emissions will slow but not stop warming, as much of the future warming is already locked in, such as the carbon dioxide temporarily in the oceans.

Holding the temperature increase to 1.5 degrees Celsius would require unprecedented social changes, Dr. Kristie Ebi, a lead author on a recent special report for the Intergovernmental Panel on Climate Change, told an audience in Tahoe recently.

If temperatures rise two degrees, the impacts will be much bigger, she said. The California water research was conducted as part of the Hyperion Project. The Colorado River Basin will also be studied in similar fashion.

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