What’s driving the massive, destructive rainfalls in U.S.
At one weather station in Fairbanks, Alaska, each hour of rainfall is about 50 percent more intense, on average, than it was a half-century ago. The Wichita area is experiencing rains about 40 percent more fierce these days. Huntington, W.Va., and Sioux City, Iowa, are seeing deluges roughly 30 percent more extreme than in 1970.
Places around the nation are facing more frequent, more extreme precipitation over time — a reality laid bare once again by the record-shattering rains and catastrophic flooding in eastern Kentucky and St. Louis last week.
The warming atmosphere is supercharging any number of weatherrelated disasters — wildfires, hurricanes, crippling heat waves. But as it also fuels once-unthinkable amounts of rain in single bursts, the problem of so much water arriving so quickly is posing serious challenges in a nation where the built environment is not only outdated but increasingly outmatched.
“The infrastructure we have is really built for a climate we are not living in anymore,” said Andreas Prein, a scientist at the National Center for Atmospheric Research who studies extreme precipitation.
The record-crushing rain in St. Louis inundated storm drains and creeks. Sewage backed up into homes. The River des Peres swelled beyond its banks. The area’s sprawling drainage systems, parts of which date to the 19th century, were quickly overwhelmed.
“What happened was way more than the system — any system — can handle,” Sean Hadley, spokesman for the Metropolitan St. Louis Sewer District, said of the recent storms that dumped more than 9 inches of rain there in a matter of hours, shattering the previous daily record from 1915.
“It was just too much water,” Hadley said.
An analysis of weather data by the nonprofit group Climate Central found that nearly threequarters of locations the group examined around the country have experienced an increase in the amount of rain falling on their annual wettest day since 1950 — particularly along the Gulf Coast and Mid-Atlantic. The numbers show that 2021 was a record-setting year for extreme rainfall events, with dozens of places logging their wettest day in generations.
Jen Brady, a data analyst for Climate Central, said many places around the country are getting roughly the same, or in some cases, less rain annually than in the past. But it is the sudden, relentless rainfalls that are contributing to flash floods and other problems.
“The damage that’s happening doesn’t show up when you just look at (annual) precipitation records. It matters if you get 2 inches a day, versus 2 inches an hour,” Brady said. “Our infrastructure is not designed to hold that much water in that much time.”
Scientists say there is little doubt about what is driving the shift toward more frequent, more devastating rains: climate change.
“Individual events happen all the time and have happened all the time in our historical record. We need to be aware that just because we have an event doesn’t mean it represents something unusual,” said Kenneth Kunkel, an atmospheric sciences professor at North Carolina State University.
But while it remains difficult for researchers to outline the precise climate fingerprint on specific summer thunderstorms and other heavy-rain events, they are increasingly able to detail the climate impact on massive tropical cyclones such as Hurricane Harvey.
“There’s no doubt that the frequency and intensity of the extreme rainfall events is increasing,” Kunkel said.
The explanation boils down to what Kunkel calls “basic physics.” For every degree that the air temperature increases, the atmosphere can hold about 4 percent more water.
The world already has warmed more than 1.8 degrees since preindustrial times. That increased heat means more moisture in the air — in the United States, much of which comes off the Gulf of Mexico — and more fuel for more intense rainstorms.
“We’ve had an increase in the amount of atmospheric water vapor … so we are seeing more of these heavy rainfall events,” said David Easterling, a scientist at the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. “This is all very consistent with the notion of a warming atmosphere.”