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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

Atlanta's Changing Storm Climate (JUNE 1999)

Item #d99jun45

In the summer, the Southeast regularly experiences afternoon thunderstorms. Atlanta, however, has also had predawn or early morning showers that continue until noon. At the annual meeting of the Association of American Geographers in Honolulu, Hawaii, on Mar. 24, 1999, Robert Bornstein and Qing Lu Lin from San Jose State University in California attributed this anomalous pattern to urban heat islands that heat the air 5 to 8 degrees (Fahrenheit) higher than in outlying areas, causing it to rise. The cooler, outlying air is then sucked in to replace the rising air mass. As the warm air ascends, the water in it cools and condenses, producing intense and localized rainstorms with thunder and lightning. The early morning rain results because the urban heat islands retain their high temperature long after nightfall. Indeed, aircraft data indicate that the pavement of parking lots can reach 120°F during the day; tree-shaded areas in the same locale only reach 89°F. Planting trees and installing highly reflective roofing materials are recommended ways to ameliorate the effects of such heat islands.