The ATLANTA project finds Atlanta's "urban heat island" increases
pollution and changes the local weather.
The sprawling metropolis of Atlanta, Georgia is an island unto itself-an
"urban heat island". A new study reports that with temperatures up
to 10 degrees hotter than surrounding areas, the metropolitan area can create
its own weather by making clouds, stirring up thunderstorms, and magnifying the
area's already severe smog problem. The research is sponsored by NASA's
Earth Observing System Program and was presented March 24, 1999 at the
meeting of the Association of American Geographers in Honolulu, HI.
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.
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, according to Luvall. Ozone is only produced in warm summer
months. Ozone is a health hazard regulated by the Environmental Protection
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.
To understand the distribution of increasing populations over the Atlanta
metropolitan area, University of Georgia geographers Chor-Pang Lo and
Xiaojun 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 will report 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 the added thunderstorms is that the
precipitation cleans the atmosphere of pollutants and cools down 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 will
report on new research to understand how large urban areas effect cloud
cover and how the clouds tend to decrease the amount of ozone production by
blocking sunlight and cooling the ground surface.
ATLANTA researchers have several ideas to combat the urban heat island and
its potentially harmful side effects. Luvall and Quattrochi offer a basic
strategy for the city to help bring down the temperature. Light color
materials could make roads, roofs and parking lots more reflective. And
planting trees and vegetation will offer shade and cool the air more
quickly when plants lose water to the atmosphere. Lowering the air
temperature by just one degree could significantly lower the ozone levels,
Quattrochi and Luvall said that the ATLANTA team is now working with state
and local government agencies to try and mitigate the effects of the urban
Atlanta Heat Island story provided couresty of Victoria Bruce, EOS Science