One of the shocking things about the storms that hit Texas this week is that rainfall of similar devastating strength struck almost exactly a year ago in many of the same places.
That tragic repetition may be less of a surprise to those who follow climate science.
While it is tricky to attribute specific rain events to climate change, experts say they know enough about how the warming atmosphere and warming oceans affect precipitation to recognize trends.
"We're not saying that our warming climate caused these floods this year, last year" Shel Winkley, chief meteorologist at Climate Central, told Texas Public Radio's The Source. "But we understand how it's making it more likely, more frequent."
A warming atmosphere, for example, increases extreme rainfall risk because warm air holds more moisture that can lead to about 4% more rainfall for every one degree warmer the air becomes, Winkley said.
In a 2024 report, the Office of the State Climatologist of Texas noted that Texas had already seen up to a 15% increase in extreme rainstorms this century from the latter part of last century.
That report predicted a 20% increase in the frequency of those storms by 2036 that would more than double the previous odds of extreme rainfall happening.
The same report found that increased rainfall will contribute to a 10% to 15% increase in flooding in urban areas, potentially doubling the risk of floods from last century.
Ocean temperatures, made warmer through heat-trapping pollution, also contribute to stronger storms.
"Right now the Gulf of Mexico, even by July standards, is above average," Winkley said. "A warmer ocean can allow for more evaporation, more rain making moisture."
None of those ingredients assure greater rainfall, but when they run into the right weather conditions, they do make the rainfall worse.
Those weather conditions were in place last week.
Typically heavy rains are kept at bay in Texas summers by an area of warmer air in the upper atmosphere sometimes called a "cap."
Bob Fogarty, a meteorologist with the National Weather Service in New Braunfels, said that cap stops the warmer, humid air blowing in from the gulf to rise up and create rain.
But, Fogarty said, ahead of this week's storms, a disturbance in the upper atmosphere "took the cap away."
"Because the air was so moist it produced very heavy rainfall," he said. "The moisture levels were unusually high for this time of year, and when it rained it rained a lot."
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