Hurricane Harvey made landfall in Texas on Aug. 26, 2017, and lingered in the region for nearly a week. As much as 60 inches of rain fell in the storm, setting a U.S. rainfall record. More than 20 inches of rain fell across about 29,000 square miles. No storm rivals Harvey, said Shane Hubbard, a researcher at the University of Wisconsin who made and mapped that calculation.
“In looking at many of these events [in the United States], I’ve never seen anything of this magnitude or size,” Hubbard said. “This is something that hasn’t happened in our modern era of observations.”
In total, about 33 trillion gallons of rain fell during Hurricane Harvey.
“Our research suggests that future hurricanes could drop significantly more rain,” said Ethan Gutmann, an NCAR scientist who led the study. “Hurricane Harvey demonstrated last year just how dangerous that can be.”
The extra rain can be explained by basic atmospheric principles — warmer air can “hold” more water vapor, which is converted to rain in storms. But the storms of the future also moved more slowly, which would lead to more rainfall.
Figuring out how hurricanes will change as the planet warms has been difficult for researchers because climate change models aren’t high-resolution, and they can’t “see” hurricanes. So NCAR scientists used a research weather model and ran it to simulate 13 years of weather — twice. The first time they ran it with today’s conditions. The second time they added nine degrees to the background climate, which is what scientists expect by the end of the century if greenhouse gas emissions continue as is.
When they looked at the results, they found several hurricanes that would be different in a warmer environment — and they were all very different storms. But there was one common theme across all of the storms in the climate-change future: They all produced more rain.