The science behind Texas’ catastrophic floods todayheadline

Rescue crews are scrambling to find survivors of catastrophic flooding that tore through Central Texas on the Fourth of July. It’s already one of the deadliest flood events in modern American history, leaving at least 95 people dead, 27 of whom were girls and counselors at a Christian summer camp in Kerr County, which was inundated when the nearby Guadalupe River surged 26 feet in just 45 minutes. 

“It’s the worst-case scenario for a very extreme, very sudden, literal wall of water,” said Daniel Swain, a climate scientist at the University of California, Los Angeles, during a livestream Monday morning. “I don’t think that’s an exaggeration in this case, based on the eyewitness accounts and the science involved.”

It will take some time for scientists to do proper “attribution” studies here, to say for instance how much extra rain they can blame on climate change. But generally speaking, this disaster has climate change’s marks all over it — a perfect storm of conspiring phenomena, both in the atmosphere and on the ground. “To people who are still skeptical that the climate crisis is real, there’s such a clear signal and fingerprint of climate change in this type of event,” said Jennifer Francis, senior scientist at the Woodwell Climate Research Center.

This tragedy actually started hundreds of miles to the southeast, out at sea. As the planet has warmed, the gulf has gotten several degrees Fahrenheit hotter. That’s turned it into a giant puddle of fuel for hurricanes barreling toward the Gulf Coast, since those storms feed on warm seawater. 

Even when a hurricane isn’t brewing, the gulf is sending more moisture into the atmosphere — think about how your bathroom mirror fogs up when you draw a hot bath. This pushes wet, unstable air higher and higher into the atmosphere, condensing into clouds. As these systems release heat, they grow even more unstable, creating a towering thundercloud that can drop extreme amounts of rainfall. Indeed, preceding the floods, the amount of moisture above Texas was at or above the all-time record for July, according to Swain. “That is fairly extraordinary, in the sense that this is a place that experiences very moist air this time of year,” Swain said. 

That meant the system both had the requisite moisture for torrential rainfall, plus the instability that creates the thunderstorms that make that rain fall very quickly. This storm was dumping 2 to 4 inches of rain an hour, and it was moving very slowly, so it essentially stalled over the landscape — a gigantic atmospheric fire hose soaking Central Texas.

Making matters worse, the ground in this part of Texas is loaded with limestone, which doesn’t readily absorb rainwater compared to places with thick layers of soil at the surface. Rainwater rapidly flowed down hills and valleys and gathered in rivers, which is why the Guadalupe rose so fast. “That means that not very much of the rain is going to soak into the ground, partly because the soil is shallow and partly because there’s steep slopes in the terrain, so that water is able to run off fairly quickly,” said John Nielsen-Gammon, Texas’ state climatologist and director of the Southern Regional Climate Center at Texas A&M University.

This is exactly the kind of precipitation event that’s increasing fastest in a warming climate, Swain added. In California, for instance, alternating periods of extremely wet conditions and extremely dry ones are creating “weather whiplash.” As the world’s bodies of water heat up, more moisture can evaporate into the atmosphere. And due to some basic physics, the warmer it gets, the more moisture the atmosphere can hold, so there’s more potential for heavier rainfall. 

“The Gulf of Mexico has been going through several marine heat waves recently, and so it’s just adding that much more heat to the atmosphere, loading it up for more extreme rainfall events,” said Brett Anderson, senior meteorologist at AccuWeather. “A lot of these places, 1-in-100-year floods may be becoming more like 1-in-50, even 1-in-10.” AccuWeather’s preliminary estimate puts the economic damage of the flooding at between $18 billion and $22 billion.

The Trump administration did make deep staffing cuts to the National Oceanic and Atmospheric Administration earlier this year, but it’s too early to tell why some people didn’t get warnings in time. The National Weather Service did indeed provide multiple flood warnings, and some people are reporting they got alerts on their cell phones, prompting them to escape. Still, with so many people dead or missing, they either didn’t get the alerts or didn’t adequately understand the danger they were in. Officials in Kerr County previously considered a more robust warning system for Guadalupe River floods, but rejected it as too expensive.

For the girls and staff at the summer camp, the deluge arrived at the worst possible time, in the early hours of the morning while they slept. “In my view — and this seems to be the consensus view of meteorologists — this is not really a failure of meteorology here,” Swain said. “To my eye, the Weather Service predictions, they certainly weren’t perfect, but they were as good as could have been expected given the state of the science.”

Swain warns that if the administration follows through on its promises of further more cuts to NOAA, forecasts of flooding could well suffer. “That really could be catastrophic,” he said. “That will 100 percent be responsible for costing lives.” 

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