CLOVIS, Calif. – A partial collapse of a glacier was likely the trigger of a devastating flash flood in Nepal that has so far left over 1,000 dead and another 4,000 missing.
The disaster a world away from California has raised a question for people who live along the state’s Sierra Nevada mountain range, where glaciers still populate its highest peaks: Could something like that happen here?
Andy Jones, a paleoclimatologist at the University of Wisconsin-Madison who has spent years studying California’s glaciers, said a catastrophic event such as the one in Nepal is extremely unlikely in California – mainly because glaciers here are smaller and the region is generally drier.
“It doesn’t seem like a similar event could happen in the Sierra Nevada,” Jones said.
But the range is not out of the clear from severe flooding risks. A potentially warm winter being brought on by El Niño isn’t leaving floods out of the question. But flooding in this case, experts say, would be driven by different natural forces.
“If we were to experience an above-normal winter, then we would have concern that most of our precipitation is liquid instead of snow,” meteorologist Nick Daer said. “So then, there would be more concern for flooding in the Sierra Nevada and the foothills.”
Glaciers in the Sierra Nevada aren’t what they used to be
200 years ago, Jones said, researchers identified nearly 100 glaciers that were tucked into many shady head walls of the Sierra Nevada mountains at elevations above 10,000 feet.
Glaciers are large bodies of ice that remain frozen year-round. They may look stationary, but are actually flowing downhill at a very slow pace and deforming under their own weight.
“If you put a stick in the ice and came back the next year, it’ll be at a different place,” Jones said, “like it actually moved.”
Once the ice stops moving, it’s considered a “dead” glacier.
Jones has been examining the history of glaciers in the Sierra with data from over tens of thousands of years – documenting current glacier loss and exploring their ecological impacts.
One finding is that these massive sheets of ice indeed seem to be disappearing.
Jones and a handful of other researchers published a peer-reviewed research journal last year in Science Advances, where they write that fewer glaciers remain in the Sierra today.
Those that remain are small remnants of the glaciers that once were active and flowing in the region.
Lyell Glacier near the John Muir Trail, and Maclure Glacier near the Pacific Crest Trail near Donohue Pass are among the handful of active glaciers in the Sierra.
Even the largest remaining glacier in the Sierra – the Palisade Glacier on the eastern edge of the Sierra – is only about a tenth the size of the glacier that collapsed last month in Nepal, according to Jones.
The disaster that happened in Nepal on Aug. 26 was primarily due to a rock landslide that took ice with it. It sent debris and water racing through the Bhote Koshi and Trishuli River valleys within minutes.
Climatologists believe that human-driven warming had melted part of a glacier upstream of the river, which removed the ice “buttress” that helped to hold up the slopes. On top of that, meltwater had been working its way into the rock fractures, causing the mountain to become weaker over time.
“The Sierra Nevada does not have this,” Jones said. “Yosemite National Park is famous for just big, exposed bedrock slabs where you’re not going to have water accumulating in the soil. The Sierra Nevada is a much drier system than Nepal.”
But Jones said the state is facing a different consequence of global warming: the loss of its glaciers entirely.
He said the Sierra glaciers are disappearing for the first time in at least 30,000 years. This past spring, record-high temperatures left no measurable snow in the last Sierra snow survey.
“What is unprecedented and probably unpredictable is the ecological impact of losing that sort of base meltwater when you have no ice in the mountains anymore, and you lose your snowpack,” Jones said.
A glacier acts as a backup reservoir that keeps rivers flowing after the seasonal snow is gone. As they vanish, streams could run dry in late summer.
El Niño could bring floods this winter
Many forecasters are warning that central California could face above-average rain this winter due to a stronger-than-normal El Niño climate pattern.
Nick Daer, a meteorologist with the National Weather Service office in Hanford, said it’s still not clear how El Niño will affect our area.
“When we're talking about an El Niño year, that means that yes, we are concerned about above-average precipitation here in California, but that doesn't necessarily guarantee that we're going to see above-average precipitation and a higher occurrence of these flood events,” Daer said.
Central California has a 40 to 50% chance of above-average winter precipitation, as of the latest winter seasonal outlook by the National Weather Service’s Climate Prediction Center. But Daer argues that the forecast is not final.
“They're currently saying that we have equal chances of being either above or below normal,” Daer said. “So it doesn't look like they have particularly strong confidence whether we're going to be experiencing a warmer winter or a cooler winter.”
The potential flooding that could come as a result of a warmer winter is something the National Weather Service and Climate Prediction Center is keeping an eye on – not just because of the additional rain, but because warm storms during the winter can melt snow earlier than normal and overwhelm the state’s water storage infrastructure.
“In California, we have very well managed and controlled waterways. We have dams and reservoirs all across the Sierra Nevada,” Daer said. “But really the concern there would be if those reservoirs are approaching full capacity, then more water than usual would have to be released, and then that's when we'd see flooding concerns in the foothills and in the valley.”
That’s the backdrop that contributed to the reemergence of Tulare Lake in 2023.
The Climate Prediction Center will come out with its next seasonal outlook in late September.
