Image of summer rain and downwind in Texas

NASA Satellite Confirms Urban Heat Islands Increase Rainfall All Around Cities

NASA researchers have for the first time used a rainfall-measuring satellite to confirm that "urban heat-islands" create more summer rain over and downwind of major cities, including Atlanta, Dallas, San Antonio and Nashville.

Dr. J. Marshall Shepherd and colleagues at Goddard found that urban areas with high concentrations of buildings, roads and other artificial surfaces retain heat and lead to warmer surrounding temperatures, and create urban heat-islands. This increased heat may promote rising air and alter the weather around cities.

"Cities tend to be one to 10 degrees Fahrenheit [.56 to 5.6 Celsius] warmer than surrounding suburbs and rural areas and the added heat can destabilize and change the way air circulates around cities," said Shepherd. Rising warm air may help produce clouds that result in more rainfall around urban areas.

Using the world's first space-based rain radar aboard NASA's Tropical Rainfall Measuring Mission (TRMM) satellite, Shepherd and colleagues found that mean monthly rainfall rates within 30-60 kilometers (18 to 36 miles) downwind of the cities were, on average, about 28 percent greater than the upwind region. In some cities, the downwind area exhibited increases as high as 51 percent.

For the complete article and images, go to: http://www.gsfc.nasa.gov/topstory/20020613urbanrain.html