Climate-driven snow drought set stage for deadly California avalanche, experts say | California

The many weeks of worrying snow drought in the western United States are driven by the climate crisis and helped set the stage for this week’s deadly avalanche in northern California’s Sierra Nevada mountains, experts say.

Perilous avalanches are not uncommon in the region, according to the National Avalanche Center, which maintains a map of where avalanche danger is highest, and the risk is now particularly high in the Lake Tahoe area.

The death toll of eight backcountry skiers so far in Tuesday’s avalanche makes it one of the deadliest in U.S. history. One skier is still missing while six others were rescued after being stranded for some time. The avalanche is now the deadliest event of its type in the United States in 45 years.

The avalanche risk became serious after several meters of fresh snow fell since Sunday, when the group of skiers began their trip, settling on an earlier layer that had hardened, making it unstable and easily triggered.

The new snow didn’t have time to bond with the previous layer before the avalanche fell, according to Craig Clements, a meteorology professor at San Jose State University in northern California.

When the weather is dry and clear, as it has been in the Sierra Nevada since January, snow crystals change and can become angular or round over time, Clements said. The new heavy snow is different and does not bind to the snowpack, forming what is called a “storm slab” on the weaker snow layer.

“Because it’s on a mountain, it’s going to slide” when triggered by any change in voltage above or below, sometimes naturally, but also from people passing through the area, Clements said.

Authorities have not said what triggered Tuesday’s avalanche.

If there had been more consistent snowfall throughout the winter, the different layers might have bonded together more easily, Clements said. But even when a patch of snow forms, the danger often lasts only a few days while the new snow stabilizes, he explains.

The climate crisis may lead to extreme weather events, including droughts and heavier precipitation. Clements said he didn’t think this individual avalanche could be directly linked to the climate crisis, and that it was “a weather phenomenon, not a climate phenomenon.”

However, the record snowpack in the West this season is mainly due to heat in the region linked to the climate crisis from the burning of coal, oil and natural gas, several scientists said.

Since December 1, more than 8,500 daily high temperature records have been broken or tied across the western United States, according to data from the National Oceanic and Atmospheric Administration (Noaa).

Much of the precipitation that would normally fall as snow and stay in the mountains for months falls as rain, which drains more quickly, said Daniel Swain, a climatologist at the University of California Water Resources Institute.

It’s a problem that scientists have been warning about with the climate crisis.

“It was so hot, especially in December, that snow was only falling in the highest parts of the mountains. And then we got into January and it was very dry almost everywhere for the last three to four weeks and stayed warm,” said Daniel McEvoy, a researcher at the Western Regional Climate Center.

The Associated Press contributed to this report