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Here Comes Urban HeatNASA scientists are using space age technology to understand how characteristics of the urban environment create "urban heat islands." |
March
16, 2000: As sweltering summer days linger just around the
corner, scientists are working to demonstrate the verity of Atlanta's
popular epithet - "Hotlanta."
Quattrochi says that two major goals of their studies are to "understand how the characteristics of the urban landscape drive this urban heat island effect and how urbanization and growth shape the dynamics of the effect." One concern is the ability of urban heat islands to create or alter weather patterns - specifically to cause thunderstorm activity.
The 1996 Olympics in Atlanta afforded scientists a chance to scrutinize data collected by the National Weather Service's ground-based meter used to predict weather for the athletes. Urban meteorologists Robert Bornstein and Qing Lu Lin of San Jose State University found that 5 of 9 days of precipitation were caused by the urban heat island effect. By analyzing Landsat 7 images from the 1970s to the present, scientists can determine trends in urbanization and rising temperatures. They found that suburban development in Atlanta gobbled up 380,000 acres of trees from 1973 to 1992. Right: Heat builds in a city when forests are cut down to build roads. Not only do paved roads hold in heat, cars also compound the problem by generating smog and more heat (inset). Photo credits: Department of Energy, Warren Gretz. "If you believe in averages," says Quattrochi, "that's 55 acres of trees per day." While much of the growth in Atlanta has been residential in nature, Quattrochi cautions that commercial and residential development often go hand-in-hand. As Atlanta expands, more trees are cleared to accommodate the growth. Trees are replaced with paved roads that retain heat and host the deluge of traffic -- traffic that now must travel the longest average daily commute in the nation. Vehicle emissions and rising temperatures also contribute to an increase in ozone, a pollutant detrimental to the environment and human health. During last year's ozone season in Atlanta, which runs from the end of April to the end of September, the city suffered through 62 straight days of ozone alerts. Quattrochi says that, based on models, there is potential for a temperature decrease of 2 degrees Celsius in Atlanta to lower the ozone by 10 to 14 percent, a significant drop. With no indication that urban sprawl will slow in the near future scientists are searching for ways to curb urban heat islands. "Why do rooftops and asphalt have to be black?" asks Quattrochi. Left: A worker installs white roofing on an Atlanta school. Photo credit: Department of Energy. Quattrochi and other team members hope that state and local governments will use their findings as a springboard to adopt "cool community measures." These alternatives include planting trees and using reflective roofing materials that can reflect 60-80 percent of incoming sunlight, more politically viable options than air quality restrictions.
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High in the Sky, NASA 'Heat Hunters' Combat Urban Phenomenon - - NASA Press Release Welcome to the Thunder Dome - Scientists will use Landsat-7 data for further research on Urban Heat Islands. (April 26, 1999 story) Stepping back to get a closer view - Scientists will use Landsat-7 data for further research on Urban Heat Islands. (April 21, 1999 story) Salt Lake City shows hot and cold spots - Mountains to east provide cool refuge. (July 21, 1998 story) Sacramento glows with Urban Heat - More data from further west. (July 1, 1998 story) NASA Climate News - research on urban heat islands. Global Hydrology and Climate Center - NASA Earth science Heat Island Group - definitions and developments of urban heat islands. |
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