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Winter 2001

Science Bits

Does deforestation trigger regional drying?

According to most numerical models, large-scale deforestation in the Amazon Basin should end up producing a warmer, drier climate across the region. However, a new study of Amazonian climate since 1950 contradicts that picture. A team from Iowa State University examined data from three sources: the National Centers for Environmental Prediction/NCAR reanalysis, the Global Historical Climatological Network, and NOAA satellite images of outgoing long-wave radiation. The team found that, while temperatures have risen slightly, so has precipitation. Rainfall amounts across the basin were roughly 20% higher in 1990 than in 1950, and satellite images show a rise in shower and thunderstorm activity from 1970 to 1999. At the same time, average sea-surface temperatures rose across the tropical Pacific and Atlantic off equatorial South America. An interdecadal analysis of the entire tropics shows an increase in moisture converging on Amazonia. The Iowa State team is now investigating whether the rise in nearby sea-surface temperatures might be driving the warmer, wetter regime across the Amazon. If so, they say, this trend could be suppressing or obscuring the true impact of deforestation on regional climate. The group suggests a closer look at the chain of physical and biological mechanisms within the land-atmosphere interface in Amazonia. They also recommend that climatic simulations of land-use impacts be lengthy enough so that interdecadal climate trends can be detected (many deforestation simulations only span a few years). Iowa State 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.

Iowa State University

Air-quality monitor from UC-Davis deployed at World Trade Center site

The massive cleanup effort at the wreckage of the World Trade Center in New York City has been assisted by air-quality experts from the University of California, Davis. The university's DELTA Group (for Detection and Evaluation of Long- Range Transport of Aerosols) specializes in round-the-clock measurement of aerosol size and composition. The WTC data are being used to monitor potential health threats such as inhalable particles, toxic metals, asbestos, and byproducts of burning plastic. On the roof of a building about a mile north of ground zero, a sampler has been taking measurements in eight size ranges, from more than 5.0 micrometers down to 0.09–0.24 micrometers. Particulates in the smallest range are most likely to go far into the lungs, according to UC-Davis professor emeritus Thomas Cahill. Early data showed strong evidence of particulates in this size range, says Cahill. The DELTA data have been helping the cleanup managers to choose appropriate safety measures at the site, such as what workers should wear (face masks, respirators, specific filters, body suits) and how long people can safely work. Analyses have been conducted by UC-Davis assistant research engineer Steven Cliff, chemistry professor Peter Kelly, engineering professor James Shackelford, and (from Lawrence Livermore National Laboratory) project investigator Graham Bench. The sampler is expected to be on site for about six months. Before it came to New York, the sampler was in Korea as part of the most recent Aerosol Characterization Experiment (ACE-Asia).

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Edited by Bob Henson, bhenson@ucar.edu
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Last revised: Thu Dec 20 16:42:17 MST 2001