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World's Climate MapNovember 17, 1999 — Parts of the central United States will likely experience more frequent drought conditions because of increasing greenhouse gases, according to a computer model run by NOAA.

Scientists at the Geophysical Fluid Dynamics Laboratory in Princeton, N.J., one of NOAA's laboratories across the nation, published their findings in the November issue of Climatic Change.

"The central U.S., which includes agricultural states such as Nebraska, Iowa, Kansas, Missouri, and Illinois, along with central Asia, and areas surrounding the Mediterranean Sea will likely experience substantial percentage reductions in soil moisture during the summer season by the middle of the next century. This means that these regions will be particularly vulnerable to more frequent drought conditions and associated reduction in crop yield," said Richard Wetherald, a meteorologist at GFDL and one of the study's authors. The other author is Syukuro Manabe, former GFDL scientist now affiliated with the Institute for Global Change Research in Tokyo, Japan.

In the study, the NOAA scientists used their computer model of the Earth's climate. Such models, which simulate the interactions among the atmosphere, oceans, land surface, and sea ice, are the primary tools used in the study of climate change and make use of the latest generation of supercomputers.

The scientists used their model to simulate change over the period 1765-2065 by incorporating the effect of increasing greenhouse gases and sulfate particles. "This is a robust result; most other models also show the same impacts on the central U.S.," said Wetherald.

However, while model-projected increases of global-mean temperature are consistent with observations, Wetherald said that "corresponding increases in drought frequency are unlikely to be statistically confirmed in the near future. Our study suggests that because of the large natural variability inherent in hydrologic processes, such as precipitation, soil moisture, and runoff, confirmation of the projected decrease in soil moisture will be difficult to detect, at least during the first few decades of the twenty-first century."

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