Study: Sierra Nevada ‘snow line’ is moving uphill
December 2, 2017
Anthony Cupaiuolo has been skiing the Sierra Nevada backcountry near Lake Tahoe since 1997. But over the last decade, he's noticed some changes.
"Outside of last year, which really sticks out as an anomaly, we haven't seen [snow] coverage down at lower elevations nearly as much as we would in the late '90s and early 2000s," said Cupaiuolo, who usually skis at least 80 days every winter, with a majority of them spent in the backcountry.
It's something he pays attention to since some of his favorite runs descend down to lake level, which sits at 6,225 feet.
"Whether that's terrain out by Emerald Bay or Mount Tallac or Flagpole Peak out in Meyers, a lot of that needs low elevation snow, so snow below 7,000 feet to fill in the rocks and Manzanita bushes," explained Cupaiuolo.
But Cupaiuolo is not the only one keeping his eye on the "snow line," the elevation at which precipitation either turns to rain or snow.
In a recent study published in the journal "Water," scientists at the Desert Research Institute reported that warmer temperatures have pushed the snow line in the northern Sierra Nevada 1,200 to 1,500 feet uphill.
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The study used data collected from remote sensors to monitor the snow line from 2008 – 2017. To expand their data set, the researchers used temperature data from other weather stations to estimate the portion of the precipitation that fell as snow in the Sierra dating back to 1951.
"The concerning thing is that the last 10 years have the steepest decline in precipitation falling as snow of any 10-year period in the 67-year station record," said Ben Hatchett, coauthor of the study.
Randall Osterhuber, a researcher at UC Berkeley's Central Sierra Snow Laboratory on Donner Summit, said the study reflects observations he's been seeing in the Sierra as well.
"On average snow lines are rising, and we're certainly seeing that at our station here on Donner Summit," said Osterhuber. "Bottom line we are seeing an ever-increasing amount of our precipitation falling as rain versus snow."
Hatchett and his team attribute the trend to warmer sea surface temperatures and a rise in winter storms called "atmospheric rivers," which they found result in a higher snow line.
But Hatchett says more research is needed.
"One of the main limitations of the study is, of course, the short period of record that we looked at in the paper," he explained. "But we think it's important to identify this potential trend and continue to monitor it because if it continues or stays higher like it's been for the last five years, that's concerning for ski resorts, water resource management and mountain ecosystems."
The Sierra's snowpack stores a third of California's water supply, which will gradually melt off in the spring into the state's managed reservoirs.
"If during the wintertime we're getting more rain and less snow and we're not building that snowpack, instead of managing that precipitation as a future resource we have to manage it immediately as a potential hazard in terms of flooding," added Hatchett.