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A deluge so extreme hit Northern California in late February 2019 that a news photographer spotted a man rowing through town in a garbage dumpster.

This type of common winter storm is TV Movie Archivescalled an atmospheric river, a formidable band of moisture (sometimes dubbed a "river in the sky") that streams over the Pacific Ocean and into the Western U.S., often dousing California.

Atmospheric rivers can pack a damaging punch. New research published Wednesday in the journal Science Advancesfound the largest of these winter phenomena cause billion-dollar flooding disasters. And they're getting worse.

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"They are becoming more intense with climate change," said Tom Corringham, a postdoctoral research economist at the Scripps Institution of Oceanography and a lead author of the study.

Critically, just small increases in an atmospheric river's intensity drive big increases in damages. "As we see more superstorms, we're going to see really big impacts on the economy," Corringham said.

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The key factor driving more intense atmospheric rivers is the physics of a warming globe. "When we trap more heat, there's more moisture in the atmosphere," explained Corringham. "Now more moisture falls as rain and snow, and we get more flooding."

The deluges are especially amplified in the case of already strong atmospheric rivers, which deliver a colossal amount of water, many times the average flow of water through the vast mouth of the Mississippi River.

"You're raising the ceiling on precipitation potential," said Daniel Swain, a climate scientist at the National Center for Atmospheric Research who had no role in the new study. "Atmospheric rivers will be more intense, delivering more water."

"It's not subtle."

According to NASA, for every 1 degree Celsius (1.8 degrees Fahrenheit) of warming, the air can hold 7 percent more water. "It's not subtle," said Swain. "The cumulative effect of global or regional warming is actually quite dramatic."

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The second part of the story is when this enhanced rainfall hits the ground. The deluges soak into the soil, but the soil can only absorb so much water. The rest of the water inevitably collects on the surface. "That ends up being floodwater," said Paul Ullrich, a climate scientist at the University of California, Davis, who had no role in the new research.

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Using 40 years of data from the National Flood Insurance Program (between 1978 and 2017), Corringham and his team found 11 atmospheric river events that resulted in over $1 billion in damages — nine of which have occurred since 1995.

Of course, not all atmospheric rivers are bad. Not nearly. Lower-intensity storms supply the Golden State with bounties of water, filling the state's colossal reservoirs and nourishing the region's famously productive farms. "We depend on them for our water supply," noted Corringham.

"Some atmospheric rivers are good, and some are disastrous," said Ullrich. "Too much of good thing, per se." (Of the 609 atmospheric rivers observed over 40 years, 110 were Category 4 and 5 storms — the two highest-rated intensities.)

Corringham expects the future to bring worsening flood damage when climate-enhanced atmospheric rivers are combined with both a rising population in the Western U.S., and consequently, more development.

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But, with today's vastly improved and often excellent weather forecasting, California can also brace for extreme storms and avoid some catastrophic flooding — specifically when they fill the state's massive dams and reservoirs.

Acknowledging that "more frequent and greater extremes in floods and droughts are likely," federal and state agencies are now testing ways to release water from California's reservoirs ahead of powerful atmospheric rivers (or other weather events) called Forecast Informed Reservoir Operations, or FIRO. A major goal is to avoid an overflowing, or damaged dam, similar to the Oroville Dam's (the tallest dam in the U.S.) failure and near catastrophe in 2017. With a deluge of water, the dam's channel for overflowing water, called a spillway, crumbled.

"The storm might be bigger than the dam can handle," said Cary Talbot, chief of the Flood and Storm Protection Division at the US Army Engineer Research and Development Center's Coastal and Hydraulics Laboratory. Talbot is a coauthor of the study.

"It gives us extra space to handle super-large events," Talbot added. "We can look ahead of it."

Mudslides in Northern California on February 14, 2019. Credit: Michael Short / AP / Shutterstock

When an extreme, potentially historic atmospheric river hits, there will almost certainly be chaotic flooding and mudslides, but at least the dams can be controlled.

Overall, the total amount of annual rainfall in California isn't expected to change much — but climate scientists project more intense deluges when it does rain. "The flood risk during the core rainy months will likely go up a lot," said Swain. "We're expecting the same amount of water, but coming in short bursts."

"It's a reminder that weather and climate matter in a big way to our communities," said Corringham. "If we don't act now to stabilize the global climate system, we risk significant damage to our economy."