Atlanta's urban expansion and its heating effects actually can influence the area's weather, according to a study led by scientists at NASA's Marshall Space Flight Center in Huntsville, Ala. The three-year analysis of Atlanta's land-use temperature and air-quality found that large urban areas like Atlanta are warmed to create their own "heat islands." The heat islands are created by removal of trees, addition of tall buildings and paving of land. During the day, dark materials like asphalt and roofing absorb heat and hold it long after the Sun sets, maintaining higher temperatures than rural areas.
During the study, researchers examined a one-month period in July 1996 when temperatures averaged 8-10 degrees Fahrenheit higher in the urban Atlanta area than in the outlying rural areas. According to researchers, that temperature difference created localized weather effects, causing at least six thunderstorms during that month.
Led by Marshall Center's Dr. Dale Quattrochi and Dr. Jeffrey Luvall, the study found when Atlanta heats up during the day, a surface thermal low air pressure dome is created, then the low pressure causes cool air to be pulled in from surrounding areas. The resulting wind convergence creates an upward flow motion, pushing up the hot air to trigger thunderstorms.
The scientists also found the higher temperatures double the occurrence of the chemical reaction that creates ozone, a major contributor to smog. Atlanta has the longest average commute of any metropolitan area, 34 miles.
The complete study findings were presented by team members Wednesday, March 24, at a meeting of the Association of American Geographers in Honolulu, Hawaii.
Researchers from four major universities assisted NASA Earth scientists in the Atlanta study. The weather patterns were discovered by team members Robert Bornstein and Qing Lu Lin, both meteorologists at San Jose State University in San Jose, Calif.
Robert Gillies, a geographer at Utah State University in Logan City, used satellite data from an instrument aboard a National Oceanic and Atmospheric Administration satellite to map the heat coming off Atlanta's urban area. The study included a 17-square mile intense hot zone in Atlanta's central business district.
The Atlanta area's population growth was investigated by geographers Chor-Pang Lo and Xiojun Yang of the University of Georgia in Athens. By studying aerial and satellite photos, they tracked vegetation loss and construction increases since 1973.
Between 1973 and 1998, 350,000 acres of forest have been replaced mainly by suburbs, according to their findings. Low-density residential areas -- mainly single-family homes -- have doubled to almost 670,000 acres.
Meteorologists Stanley Kidder and Jan Hafner, of Colorado State University in Fort Collins, are using Geostationary Operational Environmental Satellite and Landsat data to study how cloud cover tends to decrease ozone production by blocking sunlight and cooling the ground surface.
The researchers have used their findings to make recommendations for lowering the city's temperature, combating the urban heat island and its potentially harmful side effects.
Quattrochi recommends light colored roads, roofs and parking lots, which would reflect instead of absorbing heat. Replacing trees and vegetation also could significantly lower temperatures.
The study findings have been submitted to the Georgia state legislature for consideration.
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