The research offers confirmation of what atmospheric scientists have been warning of for years: a warmer world is, on balance, a wetter world. And as global temperatures continue to rise, an uptick in precipitation extremes is expected.
What the study finds is consistent with a basic tenet of atmospheric physics: For every degree Fahrenheit that air temperature rises, the atmosphere can hold 4 percent more water; this is known as the Clausius-Clapeyron relationship. Where storm clouds develop and the atmosphere is sufficiently moist, it means a warmer climate will support more intense rainfall.
“I think during that process we were a little surprised that this paper hasn’t been written before,” said Daniel Horton, a study co-author and a professor at Northwestern University, in an interview. “We know that precipitation should be increasing … but we just wanted to do a very straightforward paper that says, ‘Yep, we’re seeing it.’ ”
In the study, the authors examined daily data from more than 1,700 weather stations distributed in the Lower 48. Each had to have a continuous record dating back to at least 1951 to be included in the study.
“That doesn’t necessarily give us the whole story,” Harp said. “There may be places where precipitation intensity is increasing but frequency is decreasing. We might not know if there’s an overall increase or decrease. That’s one thing that we’re working on.”
“Overall, the area covered by the count of 1-inch rainfall days was lower than in recent years across large parts of the central and eastern U.S.,” Carbin wrote in an email. “In fact, moderate to severe drought has plagued areas of the Northeast, and extreme to exceptional drought is now expanding across part of the central U.S. Nonetheless, we have had extreme rainfall events occur in St. Louis, Dallas, eastern Kentucky, and, most recently, with Hurricane Ian in Florida.”
Despite strong trends in the central and eastern United States, the authors noted that there were a few places where rainfall did not appear to be growing more intense. The paper does detail “mixed signals in the western U.S.,” but for reasons the authors are still trying to identify.
“That [trend] didn’t hold true for the western U.S.,” said Harp, especially in the Pacific Northwest. He explained that changes in the overall placement of weather systems are “suppressing” any tendency for heavier precipitation in the West. A slight change in the location at which high and low pressure systems are anchored can have an enormous bearing on steering currents, and subsequently on how much precipitation falls in a given location.
