Three separate downpours across three states over a span of eight days this summer swept away homes, destroyed crops and left at least 39 people dead.
The intense rainfall, in Missouri, Kentucky and Illinois, broke century-old records and destroyed swaths of communities, prompting warnings from climate experts, who said the intensity and frequency of heavy rain was likely to increase as Earth continued to warm.
No one storm can be directly attributed to climate change without further analysis, but the intensity of these downpours is consistent with how global warming has led to an increase in the frequency of extreme rainfall. A warmer Earth has more water in the atmosphere, resulting in heavier rainstorms.
“We anticipate that these type of events might become even more frequent in the future or even more extreme in the future as the earth continues to warm, which means that this is kind of a call to action that climate change is here,” said Kevin Reed, an associate professor at the School of Marine and Atmospheric Sciences at Stony Brook University in New York. “It’s not a problem for 50 years from now. It’s a problem now.”
In four days, between 14 and 16 inches of rain fell in a narrow swath in the eastern part of the state, according to radar-based estimates from the Weather Service. It said that this is “historically unheard-of” and that there was a less than 1 in 1,000 chance of that much rain falling in a given year.
Earlier that week in east-central Missouri, the Weather Service said that 7.68 inches of rain fell in a six-hour period, an event that also had a 0.1 percent chance of occurring in a given year.
The deluge on July 25 and 26 was the most prolific rainfall event in St. Louis since records began in 1874, according to the Weather Service. Roughly 25 percent of the area’s normal yearly rainfall came down in about 12 hours.
Neil Fox, a professor of atmospheric science at the University of Missouri, said the heavy rain in Missouri was caused by thunderstorms developing over and over again in the same area, known by meteorologists as training. Training is a common cause of heavy rainfall and drove the downpours in Illinois and Kentucky as well.
“The amount the records were broken by, it’s like someone beating the 100 meter world record by a second or something,” Professor Fox said. “It’s an incredible increase over the previous record.”
The Illinois rainfall this week was less severe, and there were no reported deaths, but the deluge caused flash flooding and damaged crops. The Weather Service said that the highest measured rainfall in that storm was seven inches, which has a 1 percent to 2 percent chance of occurring in a given year.
“We typically get a little over three inches in the month of August, and we got five to seven inches just in the first two days here of August,” said Nicole Albano, a meteorologist at the National Weather Service office in Lincoln, Ill. “That’s pretty substantial.”
The United States and other parts of the world have seen an increase in the frequency of extreme rainstorms as a result of climate change, caused by the burning of fossil fuels like oil and gas. The frequency of these heavy downpours is likely to increase as warming continues.
“We also expect the heaviest possible precipitation events at any given location to get heavier as temperature increases,” said Angeline Pendergrass, an assistant professor at Cornell University in Ithaca, N.Y., who studies extreme precipitation. “That means we should expect more precipitation records to get broken than we would without global warming.”