Why flash floods in the U.S. are becoming more common

Data: NCEI; Map: Erin Davis/Axios VisualsStorms sweeping through the U.S. this summer have dumped intense rain on cities across the country, left towns flood-ravaged and forced water rescues. The big picture: Scientists who spoke to Axios say the deadly floods in Texas that killed more than 130 people underscores the risk that climate change can worsen extreme rainfall events.By the early hours of the Fourth of July, storms over Texas had dumped some 12 inches of rain in certain parts of the region, according to National Weather Service radar estimates cited by The Texas Tribune. But the threat didn't stop that day, with more rain falling and hindering desperate search efforts throughout the following week.Driving the news: Meanwhile, on the East Coast, Tropical Storm Chantal rapidly formed — and slowly drenched North Carolina with flooding rains.Last week, storms sparked floods in New Mexico that killed three in the Village of Ruidoso.Widespread rainfall along the I-95 corridor in the Mid-Atlantic Monday set off flash flood warnings, grounded flights and sent torrents rushing through New York City subway stations.In New Jersey, two people died after the vehicle they were in was swept away by floodwaters.Context: Climate change "is supercharging the water cycle," sparking heavier precipitation extremes and related flood risks, according to Climate Central, a climate research group.Among 144 U.S. cities analyzed by the group in a report from earlier this year, 88% experienced an increase in hourly rainfall intensity between 1970 and 2024.The summer months already provide the weather patterns for higher rainfall rates in some regions, and climate change makes that risk worse.The latest: A National Weather Service discussion warned the risk wasn't over, noting that a "[p]otent summer storm system" will bring the threat of flash flooding and severe weather "to the Midwest and northern/central Plains Wednesday."It also noted "storms will continue ahead of the cold front across the interior Northeast/northern Mid-Atlantic/Upper Ohio Valley Thursday."In Louisiana, New Orleans and Jefferson Parish is bracing for up to 10 inches of rainfall as a tropical system moves through the region.Friction point: The Washington Post reported Wednesday that the development of a tool aiming to predict how rising temperatures will impact extreme rainfall frequency had been delayed amid a Commerce Department review. A NWS spokesperson confirmed to the Post the move to delay the forward-looking part of the Atlas 15 project.But a National Oceanic & Atmospheric Administration spokesperson told Axios the administration "has not stopped the production of Atlas-15." The Commerce Department did not immediately respond to Axios' request for comment.What they're saying: "With all these events, what they have in common is that in a warmer world, our atmosphere can hold more moisture," said meteorologist Shel Winkley, the weather and climate engagement specialist at Climate Central.In Texas, he said, the remnants of a tropical system primed the area for a heavy rain event over a part of the state prone for flash floods. In a stable climate, it still would have been a significant weather event. But with climate change, "we're essentially just loading up" systems, he said. Winkley continued, "We're adding a little bit more moisture, so that allows for higher rainfall intensity. It allows for a little more heavier rain to come down, and it allows for these weather systems to become more likely and ... more frequent."By the numbers: For every 1°F of warming, the air can hold an extra 4% of moisture, per Climate Central.With climate change, the atmosphere becomes "greedier," Winkley said, meaning it can release more moisture — but it can also take more from the ground.Zoom in: In New Mexico, rain fell over an area that had been previously hit by wildfires, increasing its risk of flash floods.Similarly, the ground in areas hit by drought — like Kerr County, Texas — may not be able to handle downpours, exacerbating flash flood risk.The bottom line: With 2°C of global warming, a large majority of U.S. counties are likely to experience a 10% or higher increase in precipitation falling on the heaviest days, Winkley noted."We understand that there's an even bigger increase ... where we're headed versus where we are now," he said.Go deeper: How the Texas floods compare to the deadliest floods of the past decadeEditor's note: This article has been updated with comments from the NOAA.

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