California is at risk of disaster from the ‘second big one’, scientists warn

Californians are already living with an increased risk of wildfires and droughts linked to the climate crisis, not to mention the threat of large earthquakes on the San Andreas Fault. But now scientists are warning against potential catastrophe from the “second big one”.

New research, led by researchers at the University of California, Los Angeles (UCLA) and the National Center for Atmospheric Research, has found that the state faces a catastrophic flood that could inundate large regions with water currents hundreds of miles long and tens of miles across. .

“Every major population center in California would be hit right away — probably parts of Nevada and other adjacent states as well,” Daniel Swain, a UCLA climate scientist and co-author of the paper, said in a press release.

About a decade ago, researchers began examining modern flood risk in the state after a major disaster in 1862. During the “Great Flood”—when no flood management practices were in place—water inundated the state’s Central Valley up to 300 miles long and nearly 60 miles wide.

About half a million people lived in California then, compared to 40 million today. A similar event today would leave major cities like Los Angeles and Sacramento under water, even with flood control measures. The damage estimate is $1 trillion, the costliest ever.

The findings of the ongoing research project – dubbed “ArkStorm 2.0” to reflect the biblical scale – explain how the climate crisis will exacerbate flooding.

“In the future scenario, the storm sequence is larger in almost every way,” Dr Swain said. “There is more rain overall, more intense precipitation on an hourly basis and stronger winds.”

The study predicts that storms later in the century will create 200-400 percent more runoff in the Sierra Nevada mountain range, which runs through California and up into the western United States.

The climate crisis is likely to bring more precipitation to California, and increased temperatures mean more rain than snow will fall in the Sierras.

More runoff can lead to devastating landslides and debris flows, especially in steep areas that have previously been burned by wildfires.

The study, published Monday in the journal Science Advances, compared two extreme scenarios: one that would occur about once per century from the recent historical record, and another in 2081-2100 with projected impacts of the climate crisis.

Both scenarios would involve several storms within a month, driven by atmospheric rivers, so-called “rivers in the sky” that carry heavy rain loads.

The paper also simulated how the storms would affect parts of California at the local level.

“There are local spots that are getting over 100 fluid-equivalent inches of water a month,” Dr Swain said, referring to the future scenario.

“At 10,000-foot peaks, which are still slightly below freezing even with warming, you get 20-foot-plus snow accumulations. But once you get down to South Lake Tahoe level and lower in elevation, it’s just rain. That would be a lot more runoff.”

This article will be updated

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