WRITERS: Phil Williams, 706/542-8501, [email protected]
Victoria Bruce, 301/441-4217, [email protected]
CONTACT: C. P. Lo, 706/542-2330,
ATLANTA AN "URBAN HEAT ISLAND," WITH HIGHER TEMPERATURES
THAN SURROUNDING AREA, ACCORDING TO NEW NASA-SPONSORED
STUDY
ATHENS, Ga. -- Atlanta, Georgia, is an island unto itself -- an "urban heat island" -- that can
have temperatures up to 10 degrees Fahrenheit higher than surrounding areas, creating its own
weather and causing thunderstorms.
That's the conclusion of a new NASA-sponsored study whose results were reported recently in
Honolulu, Hawaii, at the annual meeting of the Association of American Geographers.
"We used geographic information system technology to see how land use has changed over the
past two decades," said C. P. Lo, a geographer from the University of Georgia. "It's a very
useful technique to see how land cover has changed." Lo and graduate student Xiaojun Yang
presented their data at the meeting.
All large urban areas are warmed by their own urban heat islands as a result of the removal of
trees and the paving of land, according to Dale Quattrochi and Jeffrey Luvall of NASA's
Marshall Space Flight Center, who lead the Atlanta Land-use Analysis: Temperature and
Air-quality (ATLANTA) project. Dark, heat-absorbing materials for roofs and roads create the
problem. During the day, dark materials absorb heat and hold it long after the sun sets, keeping
cities hot hours longer than outlying rural areas.
According to Luvall, the added heat intensifies Atlanta's air quality problem. The city is
plagued with serious ozone pollution. Smog levels are intensified by the urban heat island
because with a 10-degree rise in temperature, the chemical reaction that creates ozone, the
molecule responsible for smog-doubles. Ozone, only produced in warm summer months, is a
health hazard regulated by the Environmental Protection Agency (EPA).
The ATLANTA project began in 1996 to help solve the problems created and enhanced by
urban heat islands. With funding through NASA's Earth Observing System, investigators from
a variety of disciplines and institutions are looking at how land use changes since the 1970s
have intensified the urban heat island effect. New results of these studies will be presented in a
session at the AAG meeting.
"NASA had already done a study like this with Huntsville, Ala., and when it was finished, I
suggested that we do Atlanta," said Lo. "It fit well into NASA's project examining urban
environments and global change. And that's when we realized we needed many other experts if
we were to understand the effects of development on Atlanta."
To understand the distribution of increasing populations over the Atlanta metropolitan area, Lo
and Yang use aerial photos and Landsat satellite data to study the area's growth since 1973. By
interpreting these images, they can see where the vegetation is disappearing and being replaced
by roads and suburbs.
Lo and Yang reported that between 1973 and 1998, nearly 350,000 acres of forest area have
been cleared for Atlanta's 13 metropolitan counties. Replacing the forests are mainly suburbs,
according to Lo. Since 1973 the area of developed suburbs "low density residential area" has
doubled to nearly 670,000 acres. Commercial development also doubled. The expanding
population and loss of vegetated land leads to a larger urban heat island, according to Lo.
Robert Gillies, a Utah State University geographer, uses satellite data to map the heat coming
off Atlanta's urban area. When land is covered by plants or soil containing water, heat
absorbed during the day is quickly removed by evaporation and plant transpiration-the way that
plants lose water through their leaves.
From an instrument aboard a National Oceanographic and Atmospheric Administration
(NOAA) satellite that detects radiated heat from the earth, Gillies can map what parts of the city
are hotter than others, based on which areas are losing heat more quickly. Gillies will report on
the heat distribution around the city including the fact that in Atlanta's central business district
there is an intense hot zone encompassing 17 square miles (45 square kilometers).
Robert Bornstein and Qing Lu Lin, meteorologists from San Jose State University use data
from meteorological stations set up during the 1996 summer Olympics and discovered that the
urban heat island in Atlanta creates thunderstorms south of the city. When the city heats up,
low air pressure is created. Cold dense air rushes in from surrounding areas and causes the
warm air to rise. The city creates its own wind, and hot air rushes upward, triggering
convective thunderstorms, said Bornstein.
Increasing thunderstorms could cause urban flooding, said Bornstein, especially because large
areas of ground are paved and rainwater can't be absorbed into soil. One benefit of increased
thunderstorms is that the precipitation cleans the atmosphere of pollutants and cools the city.
Colorado State University meteorologists Stanley Kidder and Jan Hafner are using
Geostationary Environmental Satellite (GOES) and Landsat data to study how clouds interact
with Atlanta's urban heat island. They are experts on new research on understanding how large
urban areas effect cloud cover, which tends to decrease ozone production by blocking sunlight
and cooling ground surfaces.
"The presence of forest has a large modification effect on local climate," said Lo, "but we can't
really tell exactly where it begins or how much it changes local climate generally. What we can
say is that there is a huge increase in urban heat, making Atlanta an island in this regard."
The project team now hopes to gain funding to extend the project to include the modeling of
numerous events and land-use practices affecting the area.
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Editors note: C. P. Lo will be available for comment at the above phone number at the University of Georgia this week. After Saturday, March 20, he can be contacted at the AAG meeting in Honolulu at 808/949-4321.
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