Does urban sprawl affect the weather?

• Position: Meteorology

Previously rare big city storms--like the Aug. 19 tornado that downed trees and ripped off roofs in downtown Minneapolis and the powerful thunderstorms that destroyed scores of shade tress in New York City's Central Park a day earlier---may not be so unusual anymore. As large urban areas continue to expand, they appear to influence tornadoes and other severe weather, research suggests.

Cities could be even more at risk if located in a region experiencing a wet fall or winter, according to researchers from the Midwest and Southeast. One study---by Dev Niyogi, the Indiana state climatologist, and Marshall Shepherd, associate professor in the Department of Geography at the University of Georgia, Athens--found that drought in the fall and winter appears to decrease the number of spring and summer tornadoes in the Southeast. It is possible that particularly wet fall and winter seasons may lead to more tornado activity.

The research eventually could contribute to a system for predicting the severity of tornado season in the same way meteorologists and climatologists project hurricane season. The drought study stemmed from an earlier NASA-backed examination of a rare tornado in Atlanta on March 14, 2008. The tornado study also was done jointly by Niyogi and Shepherd, whose research focuses on understanding relationships between urbanization and land cover in general, as well as weather and climate patterns.

[ILLUSTRATION OMITTED]

The 2008 study found Atlanta's sprawling urban landscape, a prolonged drought in the region, and scattered rainfall just before the storm combined to intensify and pinpoint the tornado. The twister...