Record-breaking California bomb cyclone linked to climate change

The record-breaking bomb cyclone that barreled into the West Coast with the force of a hurricane over the weekend is just the latest example this year of extreme weather that scientists are linking to climate change.

As the deluge of rain accompanying the “atmospheric river” that took aim at central California unfolded, UCLA climate scientist Daniel Swain, who studies weather patterns and their relationship to rising global temperatures, made clear that the whiplash of years of extreme drought being broken by an unprecedented rain event was, in fact, predicted.

As the storm system pushed on land, its barometric pressure dropped to 945.2 millibars, making it the strongest storm ever recorded to hit the West Coast of the United States. Hurricane-force winds were recorded in multiple locations in the state, downing trees and leaving tens of thousands of people without power. With 4.02 inches of rain, San Francisco set a record for the most rain on an October day in the city’s recorded history. Sacramento received 5.44 inches, an all-time single-day record that came on the heels of another notable milestone: 212 days with no measurable precipitation.

A pedestrian walks on a flooded street in the rain next to two partially submerged cars.
A pedestrian on a flooded street Sunday in Kentfield, Calif. (Justin Sullivan/Getty Images)

In a paper published in 2019 in the journal Nature Climate Change, Swain examined how global warming made such dramatic shifts possible.

“Mediterranean climate regimes are particularly susceptible to rapid shifts between drought and flood — of which, California’s rapid transition from record multi-year dryness between 2012 and 2016 to extreme wetness during the 2016–2017 winter provides a dramatic example,” the summary of the paper states.

While much of the Western U.S. continues to suffer from extreme drought, the weekend’s deluge across the northern half of California proved a jarring contrast. Rainfall records were broken in multiple locations, while multiple feet of snow piled up in the Sierra Nevada mountains above elevations of 8,000 feet.

On the bright side, the deluge, which followed several days of rain the week before, brought a swift end to California’s brutal fire season, which will almost certainly mean 2021 will not break the record set in 2020 for the most acres burned by wildfires in the state’s history.

The storm also gave badly depleted California lakes and reservoirs a much-needed reprieve.

While Northern California is now cleaning up from the historic storm, the southern half of the state is forecast to get far less rain, and the drought is expected to persist, as are conditions favorable for wildfires.

Even in the areas that saw record rainfall, erasing a drought that has lasted for years is not so easily accomplished.

“Even with 5 inches of rain in Sacramento, our deficits are immense,” Jeffrey Mount, a geologist and water expert at the Public Policy Institute of California, told the Sacramento Bee. “We’re basically missing two years of ‘precip’ in this basin.”


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