Volume 5, Number 4     July/August 1997

Advanced Technologies

Hot Cities Turn to Cool Mother Nature

ASA RESEARCHERS ARE USING SPACE AGE technology to study how "urban forests" may allow cities to continuously grow whil maintainging air quality and the environment and lower colling costs during sweltering summer months.

Global Hydrology and Climate Center researchers at Marshall Space Flight Center are studying Atlanta to learn how rapid urbanization affects temperature and air quality to find out what can be done to lessen the impact.

Thermal views of Atlanta are helping researchers determine the effects of urbanization on a city's climate.

Dr. Jeff Luvall and Dr. Dale Quattrochi are studying urban heat islands, bubble-like accumulations of hot air, that have developed as Atlanta has grown during the past 20 years. "Urban heat islands result when naturally vegetated surfaces are replaced with asphalt, concrete, rooftops and other man-made materials," said Quattrochi.

They are studying the effect of tree cover on Atlanta's temperature and air quality. Atlanta's urban planners can use the findings to determine the benefits of developing and maintaining urban forests. Power requirements could be reduced with building plans that incorporate trees to shade roofs which reduce the heat load on houses and buildings.

Organized planning of "urban forests" in cities like Atlanta may counteract temperature rises caused by overdevelopment.

Quattrochi said the artificial surfaces temperatures can be 20° to 40° higher than vegetated surfaces temperatures. "Materials, such as asphalt, store much of the sun's energy and remain hot long after sunset. This produces a dome over the city of temperatures 5° to 10° higher than air temperatures over adjacent rural areas," Quattrochi said.

"The more a city grows— replacing trees and grass with buildings and roads— the warmer it becomes, increasing peak power demands. To meet these demands, power plants must utilize fossil fuels to a greater extent, which ulimately have a negative impact on air quality," said Luvall.

In findings from similar studies, the two researchers found that city parks and other urban areas with trees and grass were cooler than parking lots and areas with a high concentration of buildings.

"These 'green areas' are cooler because they dissipate solar energy by absorbing surrounding heat and using it to evaporate water from leaves, thereby cooling the air," said Luvall. Urban forests also help cool cities by shading surfaces like asphalt, roofs and concrete parking lots, preventing the initial heating and heat storage.

Atlanta's hot spots were determined by a Lear Jet equipped with thermal imaging equipment which flew over the metropolitan area May 11th and 12th taking heat images at mid-day at peak heat and again 12 hours later when surfaces began to cool.

For more information, contact Dr. Dale Quattrochi at Marshall Space Flight Center.
Call 205/922-5887 E-mail: dale.quattrochi@msfc.nasa.gov
Please mention you read about it in Innovation.