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Study: Climate change doubles risk of ‘megaflood’ across California

When you think of natural disasters in California, wildfires, earthquakes and drought often come to mind. But KPBS reporter Jacob Aere takes a look at a new study that says the risk has increased for a different natural disaster — a megaflood washing across parts of the Golden state.

The likelihood of a “megaflood” occurring in California has doubled due to climate change, according to a new study in Science Advances.

Marty Ralph is the director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography.

He helped lay the groundwork for some of the research and projections on mega-flooding events in California.


“The chance of bigger floods is very real. They’re rare, but not as rare as they were before the climate has been warming,” Ralph said. “They're looking at 200-year storms being something more plausible every 50 years.”

The study said it’s possible parts of major cities such as Los Angeles and Sacramento would be underwater if the state endured the kind of winter flooding that took place during the state’s Great Flood of 1862.

“Since that time, there’s been a major array of large flood control and water supply dams in the Sierra Nevada that have the capacity to hold back a lot of water,” Ralph said. “They’re designed partly to help offset flooding.”

Even with the many technological advancements over the last 160 years, Ralph said more preventative measures are needed.

That's because each additional degree of global warming increases the likelihood of a megaflood.


“The storms will be warmer and larger areas of the mountains will receive rain instead of snow in these storms,” he said. “When it comes to generating runoff in real time, in short term from the storms, it'll be that much more coming down the rivers quickly than would have been the case when the storms were colder.”

The study estimates that a flood like the one that happened in 1862 could be a $1 trillion disaster in today’s world, which would be the largest in U.S. history.

Study: Climate change doubles risk of ‘megaflood’ across California

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