The average snowpack in the Tahoe Basin could decline 40 to 60% by 2100 and some years could see all rain and no snow. That’s according to climate change forecasts released this week by the UC Davis Tahoe Environmental Research Center.
The decrease in snowpack would be driven by two processes, according to study author Geoffrey Schladow. With warmer temperatures, more precipitation will fall as rain during the winter, instead of snow. And as any skier knows, when rain falls on snow, it melts the snowpack in what scientists call “rain-on-snow” events.
These findings are a concern since the Sierra Nevada snowpack is often called California’s “frozen reservoir.” That reservoir is critical to the state’s water supply — and it’s free. “What the snowpack affords us is a way to very economically store water,” said Schladow. “If the water is falling as rain, rather than snow, then we have to build more dams and reservoirs to catch it, which is expensive.”
The study also forecasts several climate change impacts on Lake Tahoe itself. Prolonged droughts in California could cause the lake level to fall below out-take valves, which feed the Truckee River. The Truckee supplies water to Pyramid Lake and the city of Reno, Nevada. Output levels have fallen in the past, but under the worst case climate change scenario, those periods could stretch 10 to 20 years.
That would also change the face of the iconic lake. “Suddenly lakefront homes would be hundreds and hundreds of feet from the water. It’s going to be a very different looking lake,” said Schladow.
Lake Tahoe’s unique ecology could also change. Mixing of water from different depths is a critical process for any lake, since it takes oxygen from the surface and makes it available for fish and other species living throughout the water column. Because Lake Tahoe is so deep, today it only mixes fully every three to four years. By the second half of the century, that mixing period will become longer. “At some point, it may not mix for decades at a time,” said Schladow.
Schladow says the study focused on Lake Tahoe as an important case study for changes happening throughout the Sierra Nevada. “These same processes are happening everywhere across the West. Tahoe is the canary in the coal mine.”
Forecasting climate change impacts like these at the regional level has become a Holy Grail for climate scientists. Historically, computer climate models could only scale down to sections of land hundreds of miles across, which made it difficult to predict changes in a landscape as varied as California.
Schladow says newer climate models allow them to see changes at a much more granular level. “What we were able to do is to use grids that were more like one or two miles. That way we could distinguish between effects at the mountain peaks and effects down at the lake level.”
Schladow is hopeful that this study can give land and water managers an early indication of what the future may hold.