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.