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Science Forum Index » Environment Forum » Urban heat, pollution found to mess up weather
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| David Naugler |
 Posted: Mon Dec 22, 2003 10:23 am |
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From:
http://www.cnn.com/2003/TECH/science/12/16/urban.climate.ap/index.html
Urban heat, pollution found to mess up weather
SAN FRANCISCO, California (AP) --The massive amounts of heat and
pollution that rise from the world's cities both delay and stimulate
the fall of precipitation, cheating some areas of much-needed rain and
snow while dousing others, scientists said.
The findings support growing evidence that urbanization has a sharp
and alarming effect on the climate, and those changes can wreak havoc
with precipitation patterns that supply life's most precious resource:
water.
"These are going to become big issues," said Steve Burian of the
University of Utah.
Details were presented Thursday and Friday at the fall meeting of the
American Geophysical Union.
In California, eastward-blowing pollution induces a precipitation
deficit across the Sierra Nevada mountain range equal to about 1
trillion gallons of water a year, said Daniel Rosenfeld of Hebrew
University in Jerusalem.
The Sierra Nevada is a major source of water for much of California,
which relies on it to supply its cities and farms.
"It amounts to significantly less amounts of water," said Rosenfeld,
who has noted similar pollution-linked deficits in Israel.
The warmth and grit generated in urban areas can have the opposite
effect on local precipitation and actually boost rainfall levels in
large cities.
During the past 60 years, while Houston has grown to become the United
States' fourth-largest city, scientists have measured increased
amounts of rain in areas downwind of the urban core during hot, humid
summer months, Burian said.
"The majority of evidence is pointing to some sort of urban
modification," he said, adding that more research is needed.
Cities produce large amounts of a class of pollutants called aerosols,
which include tiny particles of dust and the byproducts of the
combustion of diesel and other fossil fuels.
Atmospheric levels of the pollutant are closely tied to levels of
human activity. In New York City, measurements made between June and
September 2001 showed that aerosol levels regularly grew during the
work week, with a noticeable spike on Wednesdays, then decreased on
the weekend, said Menglin Jin of the University of Maryland at College
Park. She attributes the midweek spike to a sharp increase in diesel
truck traffic.
When hoisted skyward, the microscopic pollutants act as multiple
surfaces on which the moisture in clouds can condense to form tiny
droplets. That can prevent or delay the formation of larger raindrops
that more readily fall from the sky as rain.
In southern California, a 24 percent decrease in the amount of
rainfall measured since 1890 in the town of Cuyamaca appears linked to
aerosol pollution wafting from San Diego, roughly 40 miles ( 64
kilometers) to the southwest, Rosenfeld said.
Cities also generate and trap tremendous amounts of heat and are on
average one to 10 degrees warmer than surrounding undeveloped areas.
That heat also changes the dynamics of clouds.
In more humid cities, urbanization appears to invigorate summer storm
activity by allowing clouds to build higher and larger before
unleashing torrential rains, Burian said. That appears to be the case
in Houston.
The relative contributions that urban heat and pollution make to
altering the climate remains unclear, scientists said. It's also
unclear what, if any, effect smaller cities might have.
"How big does a city need to be? We don't know. The answer is still
out there," said Marshall Shepherd, a NASA research meteorologist. |
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| Roger Coppock |
| Posted: Mon Dec 22, 2003 3:06 pm |
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David posts pro environmental articles, too.
Probably because he/she/it/they doesn't/don't
read before they post.
--
"One who joyfully guards his mind
And fears his own confusion
Can not fall.
He has found his way to peace."
-- Buddha, in the "Pali Dhammapada,"
~5th century BCE
-.-. --.- Roger Coppock (rcoppock@adnc.com)
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
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