Risk of catastrophic mega-floods doubled in California, study finds | Climate crisis in the American West

Driven by the climate crisis, extremely rare mega-floods will become more common – and more catastrophic – according to a new study that found their likelihood had already doubled in California.

The unexpected threat lingers even as the browned hills, fallow fields, and tub-filled reservoirs are a constant reminder of the state’s drought catastrophe, which can be horribly ill-prepared when play inevitably falls.

“Socially, from a public policy perspective and building climate adaptation infrastructure, we are falling behind,” said Dr. Daniel Swain, study author, ARkStorm 2.0: Climate Change Is Increasing the risk of a mega-flood in California, and a climatologist at the Institute for Environment and Sustainable Development at the University of California, Los Angeles.

“Our goal in doing this work is to get as far ahead of the curve as possible in terms of megaflood risk,” he said. “We know it will eventually happen and that climate change increases the odds.”

By combining high-resolution climate and weather models, scientists were able to analyze two distinct scenarios – the current danger and a future where risks are amplified by the climate crisis. The approach provides an accurate picture of what is to come. The researchers found that with a high emission trajectory, the annual probability of a 200-year event would increase by 683% by 2060.

They relied on the results of a 2010 analysis called “ARkStorm”, led by the US Geological Survey with an interdisciplinary team, which concluded that a series of severe storms had the potential to bombard the state with enough of rainfall to displace millions of people, damage critical infrastructure and transportation corridors and cause nearly $1,000,000,000 in economic losses.

brown muddy river flowing through a charred landscape
The Klamath River is brown with mud after flash floods hit the McKinney Fire. Photograph: David McNew/AFP/Getty Images

The hypothetical event has been dubbed California’s “other big” in reference to a large-magnitude earthquake expected to strike in the future. But this mega-flood would rival even earth tremors, exceeding the damage “by a considerable margin”, according to the study. Flooding is worsened by wildfires and drought, which alter landscapes and make debris flows more likely when water levels rise.

Floods in California differ from other parts of the world and are usually caused by atmospheric rivers – strong storms that release large amounts of water at once. A long sequence of them, where severe storms follow each other in quick succession, could quickly overwhelm landscapes and infrastructure. And, while wetting storms were once welcome in the parched state, “atmospheric river storms in a warming climate are likely to go from mostly beneficial to mostly dangerous — that’s a big shift,” said Swain.

Already, the state has had to deal with whiplash when it comes to extreme weather conditions and it is not alone.

In the past two weeks alone, there have been at least four extreme floods in the United States, events once considered 1,000-year storms with a 0.1% chance of occurring in a year. given. Extreme precipitation events have increased 55% in the northeast since the 1950s, according to the federal government’s National Climate Assessment, 42% in the Midwest and 27% in the Southeast.

But in the west, where the focus is on drought, states like California may be even less prepared for rising waters.

“[Warming] is both expelling winter storms, making them more extreme and amplifying flood risk, but also supercharging the atmosphere’s ability to suck this water from the landscape and also worsening droughts said Swain, calling the problems two sides of the same thermodynamic coin.

Testing the resilience of the country

California typically has a rainy season during its winter months, and the state depends on the accumulation of snow generated during this time as a saving account of water, which slowly drains into rivers and streams. But warming has brought less snow and more rain, a problem that both increases the risk of flooding and leaves less water to use during dry spells. The water also doesn’t go as far as it used to. Thirsty landscapes need more to survive the heat while the atmosphere is more adept at quickly sucking moisture from the ground.

Compounding disasters, or the layering of overlapping disasters such as drought, floods and fires, are already testing the country’s resilience and straining its resources. As they become more likely, agencies are struggling to keep up, both in California and beyond.

“The field of emergency management is at a pivotal moment in its history,” Fema Administrator Deanne Criswell said during a House Homeland Security Subcommittee hearing on preparedness, emergency response and recovery. The agency is handling more than triple the number of disasters this year than a decade ago.

fire burning in a forest with black smoke swirling around
Flames creep uphill in Klamath National Forest. Photograph: David McNew/AFP/Getty Images

Last year, the United States spent an alarming $145 billion on natural disasters – the third highest amount on record – and faced 20 extreme events that cost more than $1 billion. dollars each, almost triple the average since 1980. The Federal Emergency Management Agency (Fema) is already preparing for an escalation in needs this year and beyond, requesting $19.7 billion for its 2023 disaster relief fund.

“Climate change is the greatest crisis facing our nation and is making natural disasters more frequent and more destructive,” Criswell said. “Although our mission itself has not changed, our operating environment has changed.”

Swain said he hopes officials will heed the call from the findings of his work and other climate scientists who have described the threats.

“This has major implications for public policy and disaster preparedness,” he said. While this approach was tailored specifically to California and its unique weather conditions, he hopes the work can help frame research on megaflood risk in other regions as well.

“No one could argue that we didn’t see it coming if and when it did,” Swain said. “There is still potentially time to do something before things get messy.”

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