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NEWS RELEASE

10-09-01

Contacts:
Tsing-Chang (Mike) Chen, Geological and Atmospheric Sciences
(515) 294-9874
Eugene Takle, Geological and Atmospheric Sciences, (515) 294-9871
Skip Derra, News Service, (515) 294-4917

ISU RESEARCHERS SEE IMPACT OF GLOBAL
CLIMATE PATTERNS ON DEFORESTATION

AMES, Iowa -- Global climate patterns apparently are muting the effects of deforestation. As a result, the true effects of deforestation might be far worse than what is currently detected, according to a team of Iowa State University researchers.

Massive deforestation, like what is taking place in the Amazon Basin of South America, is predicted to result in a general warming and drying of that land mass. But over a recent 40-year period what actually has happened is a 20 percent increase in rainfall, which appears to be the result of global climate patterns.

Understanding the effects of long-term global climate patterns on areas like the Amazon Basin could have important implications ranging from determining the true effects of deforestation and reforestation efforts in parts of those areas, to altering soil erosion and the ability of species to re-emerge in altered areas.

The researchers -- ISU geological and atmospheric science professors Tsing-Chang "Mike" Chen and Eugene Takle, and graduate students Jin-ho Yoon and Kathryn St. Croix -- describe their research in the October issue of the Bulletin of the American Meteorological Society. The work, described in the paper "Suppressing Impacts of the Amazonian Deforestation by Global Circulation Change," is the first study to consider "interdecadal" changes in deforestation data.

They have found that interdecadal changes, changes that happen over decades of time, are in fact having a profound effect on the Amazon Basin. One manifestation is the 20 percent increase in rainfall, which appears to be caused by worldwide shifts in rainfall patterns. These large-scale forces, Chen says, have not been incorporated in previous deforestation studies but their role could be significant.

"Many scientists have studied the effects of deforestation, but no one has paid much attention to interdecadal change," Chen said. "That is a very important component missing from the studies. It needs to be considered to get a true reading of the effects of deforestation."

"We believe that deforestation by itself will cause warming and drying of the Amazon region," added Takle. "But over the past 40 years, global circulation patterns have been pumping extra moisture into this region from the outside.

"We expect in coming decades that this pattern may reverse," he explained. "If and when that happens, then the deforestation drying that everyone expected will be made even worse by the drying due to the reversal of the global circulation. There may be drought never before experienced in this region. We likely will see effects much worse than those described by current deforestation-impact models."

Several sources estimate that most of the Amazon forest will disappear in less than 100 years. Numerous computer simulations predict that when the rain forest is cut down, it effectively will turn that land into pastureland, and higher surface temperatures, less evaporation and less rainfall will result.

The ISU researchers looked at existing data covering the period of 1950 to 1990. Most data used in predicting the effects of deforestation only cover a period of a few years.

The ISU researchers analyzed data from the Global Historical Climatology Network, data gathered on outgoing long-wave radiation (satellite data to estimate precipitation) and of NCEP-NCAR re-analysis data (surface- and balloon-based measurements) over the Amazon Basin.

The team found that in addition to other forces at work in the Amazon Basin, water vapor converging globally in tropical South America was an over-riding force. This convergence caused the increase in rainfall during the 40-year period, a time of significant deforestation of the area.

"This outside moisture swamped what everyone expected might happen and actually caused rainfall to increase," Takle said.

Because of this effect, Chen added, efforts to measure reforestation during this period would not be accurate.

"The increased precipitation has suppressed the full, positive or negative, impact of deforestation," he said. For example, increased precipitation could have aided reforestation of the area, but it also may have hastened soil erosion.

"We learned that studies assessing the impact of deforestation in the Amazon Basin must take into account changes in global circulation patterns in order to really tell you what to expect due to deforestation," Chen explained.

While the ISU study focused on the Amazon Basin, Chen said other areas experiencing large scale deforestation should also be studied in the future. Southeast Asia, Malaysia and Africa are experiencing massive deforestation. He added that a better understanding of global climate patterns would be helpful because what happens in South American might not hold for Africa.

"Changes in global circulation is like studying a wave," he said. "There maybe water vapor convergence in the Amazon, but there may be divergence in other places."

All of which points to the need for a better understanding the major forces at work.

"There are millions of dollars being spent and many national and international research projects studying the effects of deforestation in the Amazon," added Takle. "Unless they take into account this outside influence, they may draw erroneous conclusions about what happens after deforestation."

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