Extensive long-term study links increasing temps with heavier rainfall
By Summit Voice
FRISCO — Heavy rains are becoming more common in the upper Midwest, and the trend in precipitation is linked with increasing temperatures in the region, according to University of Iowa researchers who studied daily measurements at 447 rain gauge stations in the central and southern United States.
Each site in the study has a record of at least 50 years. The data cover much of the 20th century and the first decade of this century. The states included in the study are: Minnesota, Wisconsin Michigan, Iowa, Illinois, Indiana, Missouri, Kentucky, Tennessee, Arkansas, Louisiana, Alabama, and Mississippi.
The scientists made it clear that global warming may be a significant factor in trend, but acknowledged that regional changes in land use patterns and irrigation may also play a role.
But it’s clear that warmer air can hold more water vapor. The more moisture available for precipitation means a greater chance for heavy rains, said Gabriele Villarini, assistant professor in engineering at the University of Iowa and lead author of the paper, published in the Journal of Climate, the official publication of the American Meteorological Society.
“We found that there is a tendency toward increasing trends in heavy rainfall in the northern part of the study region, roughly the upper Mississippi River basin,” Villarini, said. “We tried to explain these results in light of changes in temperature. We found that the northern part of the study region—including Minnesota, Wisconsin, Iowa, and Illinois—is also the area experiencing large increasing trends in temperature, resulting in an increase in atmospheric water vapor.“
Villarini said the current Midwest drought is not included in the study period.
“I’m not looking at the average annual rainfall. I’m studying heavy rainfall events,” he says. “We may currently be in deficit for overall rainfall, but we may also be in the normal range when it comes to the number of heavy rainfall days.”
The research was funded by NASA and the Willis Research Network.