U.S. Clean Air Act increased Atlanta rainfall

Jeremy Diem, an associate professor in the Department of Geosciences, analyzed summer rainfall data from nine weather stations in the Atlanta metropolitan area from 1948 to 2009. He discovered that precipitation increased markedly in the late 1970s as pollution decreased following passage of the Clean Air Act of 1970.

Diem also noted that pollution in the 1950s and 1960s caused rainfall to drop in the Atlanta area.

Previous studies have found a general link between air pollution and rainfall, with higher concentrations of particulates in the air suppressing rainfall.

Diem's research shows, for the first time, that a substantial decrease in pollution in a specific metropolitan area caused an increase in rainfall, Diem said, noting the findings are likely to apply to other urban areas across the United States that saw similar pollution decreases.

"Really, the only plausible reason for this increased rainfall is the reduced pollution due to the passage of the Clean Air Act," Diem said. "This probably happened in many cities other than Atlanta."

The study may also have implications for other urban areas around the world that may be experiencing drop-offs in rainfall due to pollution, Diem said.