Cities May Make Their Own Weather
By ERIN McCLAM
Associated Press Writer
12:02 PM ET 07/09/00
ATLANTA (AP) - Forecasters have known for decades that big
cities trap the sun's rays, holding the heat in asphalt and
concrete and staying consistently warmer than their suburbs. But new research suggests that the ``urban heat islands'' of
sprawling metropolises can actually create weather, churning out
thunderstorms that dump rain hundreds of miles away. National Aeronautics and Space Administration scientists
discovered the pattern in Atlanta, a sprawling metro area
increasingly choked by traffic and smog. They were interested in
Atlanta, in part, because it has few natural boundaries to contain
the sprawl.
``The island is getting bigger, and it's causing changes in the
climate all over the region,'' said C.P. Lo, a University of
Georgia geography professor who worked on the NASA project. ``There
are other cities developing similar trends, but Atlanta is the
worst-case scenario.''
Major cities soak up heat all day in asphalt, concrete and
buildings. In Atlanta, for example, the NASA team found that
95-degree days could cook rooftops to temperatures higher than 170
degrees.
When the sun sets, the cities release what they've stored in a
sweltering sigh, giving off heat in a column of low pressure. The
low pressure sucks in cooler air, and the collision creates clouds
and thunderstorms.
Scientists are certain the storms are manmade because they occur
at different times and on different days from naturally occurring
summer storms, which can happen just about anywhere as the daytime
air cools.
``The storms are occurring in Atlanta at very strange times, as
opposed to your typical garden-variety storm,'' said Dale
Quattrochi of NASA's Marshall Space Flight Center in Huntsville,
Ala. ``These are occurring at 2 o'clock in the morning.'' The manmade storms plod eastward, just as other storms do.
Scientists said they watched storms created by the heat of downtown
Atlanta soak towns on the Georgia-South Carolina line, nearly 150
miles away.
Such rain may seem like a blessing for states like Georgia,
where farmers have been wracked by drought for three years. But
researchers say the manmade storms are a sign of a dangerous trend
- an increasing number of cities with stifling, unhealthy air. The scientists' study of Atlanta was paid for by a NASA grant.
They also have studied Salt Lake City, Baton Rouge, La., and
Sacramento, Calif., using money from the federal Environmental
Protection Agency.
Scientists have studied urban heat islands for decades. In New
York, researchers noticed years ago that oncoming thunderstorms
were splitting around the city, sheared off by the patch of
hovering heat. But in Atlanta, the new research showed storms popping up around
the city on otherwise clear days.
A major contributing factor is that developers recklessly chop
down trees to make room for suburbs, the scientists said. Trees
provide shade from the heat and absorb many of the sun's harmful
rays. Without them, the effect is a sort of urban desert. ``There's a slash-and-burn mentality of building suburbia,''
Quattrochi said. ``Just kind of knock them down because it's
cheaper.''
For the past 25 years, Lo said, Atlanta has lost about 55 acres
of trees - the equivalent of 45 football fields - every day. ``You get a bigger piece of land, and you get a lawn, but
there's a downside of this,'' he said. ``The development is very
fast, and that has brought along monumental changes in quality of
air, in driving and congestion. Quite a few people are very
concerned about this.''
Those people include Georgia Gov. Roy Barnes, who wrote a letter
to NASA Administrator Dan Goldin praising the Atlanta study. Barnes
said its lessons would be critical to a future of ``sustainable
development and environmental protection'' in Georgia. In addition to traditional smog-fighting suggestions like mass
transit and urban revitalization, Quattrochi urges ``cool
community'' planning.
He says there's no reason why rooftops must be black, a color
that traps heat. He urges cities to plant trees in strategic
places. And he points out that concrete, while more expensive,
absorbs much less heat than asphalt pavement.
The scientists hope to learn more this summer about how cities
make weather - specifically, about how heat islands might affect
regional weather and tornado activity. They plan to study Los
Angeles - the nation's famous smog capital - as well as Phoenix,
Chicago and Houston.
And they want to look at cities that haven't yet developed into
large metropolises - like Nashville, Tenn., whose leaders want to
make sure their city learns from others' mistakes.
``They're really scared,'' Quattrochi said. ``They don't want to
turn into another Atlanta.''
Related Links:
www.ghcc.msfc.nasa.gov
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