Study Suggests Amazon Deforestation Could Affect Climate in U.S.

New mathematical simulations of climate behavior by Duke University
researchers indicate that deforestation in the Amazon can cause a
reduction of rainfall in the Midwestern United States and the Dakotas in
the summer, when precipitation is most needed for agriculture.

"What this suggests is that if you mess up the planet at one point, the
impact could have far-reaching effects," said Roni Avissar, chairman of
the Department of Civil and Environmental Engineering at Duke's Pratt
School of Engineering. "You have to be careful not to look at only one
area."

Avissar and research associate David Werth report their findings in the
Oct. 27 issue of the "Journal of Geophysical Research-Atmospheres." The
study was supported by grants from the National Aeronautics and Space
Administration.

They conducted their research by using as a climate simulator a set of
mathematical equations that describe the behavior of Earth's
atmosphere. Each simulation uses a variety of data such as heat release,
humidity, evaporation, precipitation, sea surface temperatures, soil
moisture transfer and the like that would exist under different scenarios
ranging from current conditions to a completely deforested Amazon basin.
It has been estimated that 15 percent of the Amazon rain forest already
has been cut and turned into pasture, but the researchers looked at what
might happen if the entire Amazon were converted to pasture land.

"Basically, what we see is a reduction of rainfall over the Amazon," Avissar
said in an interview. "This reduction of precipitation occurs most of the
year but is most significant -- on the order of 15 percent to 20 percent --
during the summer, from February to March. Of particular interest is that
we see a correlation with climate changes, primarily reduced
precipitation, in other parts of the world."

Avissar said the simulation showed a noticeable reduction of precipitation
-- 10 percent to 15 percent -- during the summer in the Dakotas of the
United States and in the Midwest Triangle of Oklahoma, Arkansas and
Missouri. Central America and the Gulf of Mexico also had reduced rainfall
in the simulation, as did an area over the western Pacific Ocean and a
region over the Indian Ocean.

Just what is happening in such simulations is not clear, Avissar said, but
the climatic mechanisms may be similar to altered wind circulation that
suppress Atlantic Ocean hurricanes during the Pacific Ocean warming
phenomenon called El Nino.

Avissar said he could not blame recent drought conditions in the United
States on deforestation in the Amazon because the Duke simulations
looked at a hypothetical situation that is much more severe than what
currently exists in the Amazon, which covers nine times as much land as
Texas.

"What we say here is that if you modify the landscape of the Amazon, it
affects other parts of the world. It is not enough for a country to make
national decisions about land use because it does not just affect the
water resources of your own country."

He and Werth are now looking for similar effects of deforestation in other
parts of the globe. They also are developing a more refined mathematical
model that may be able to predict the results of partial deforestation,
Avissar said.