WEDNESDAY, June 23 (HealthDay News) -- If global warming does drive temperatures upward, cities with urban sprawl may be more prone to extreme heat than less spread-out centers, new research suggests.

That means that sprawling metro-regions such as Tampa, Grand Rapids and Atlanta may be experiencing very hot days at more than double the rate of more dense cityscapes such as Chicago, Boston and Baltimore, said study lead author and urban planner Brian Stone of the Georgia Institute of Technology.

The difference may be caused in large part by deforestation, according to Stone. Between 1992 and 2001, such clearing of the "green" cover of trees and other vegetation -- previously shown to contribute to rising temperatures in cities -- was underway at more than twice the rate in sprawling regions than in dense urban centers.

Stone and his colleagues -- who report their findings online in the June 22nd issue of Environmental Health Perspectives -- base their observations on an analysis of the number of very hot days that occurred between 1956 and 2005 in 53 U.S. metropolitan regions. "Very hot days" were defined as being higher than 85 percent of the heat stress index, which combines temperature and humidity.

"Factors that affect whether an area remains compact include, among others, local land-use regulations and the timing of a city's growth," Stone noted in a journal news release. "Boston grew when streetcars were popular, and Atlanta developed during the era of the automobile."

The authors found that while the annual number of very hot days went up by 5.6 days a year in dense urban centers, it shot up to 14.8 days annually in the nation's most sprawling cities.

"These findings show that the pace of climate change is greater in sprawling cities than in others, which has not been shown before," Stone said. "Because severe heat kills more people on average per year than any other type of dangerous weather, residents of sprawling cities may be more vulnerable to this significant health threat posed by climate change."

The research team's analysis was based on data gleaned from the 2000 census, which documented population density, closeness of commercial and residential buildings, and street patterns. The National Climate Data Center also provided information on weather patterns.

More information

There's tips on protecting yourself during extreme heat at the U.S. Centers for Disease Control and Prevention.