Shift from forest to crops lowers te...( r highest level theMidwest had caught...)

r highest level, the Midwest had caught up to match the Northeast with 50% of its land area cultivated. Cropland area steadily declined in the Northeast as forests returned; the spread of midwestern fields continued for the next 100 years, peaking at about 80% in the 1980s. Cropland in the Northeast is now less than 20% of the region.

To make sure that the results he was seeing were not happening in only one decade of the temperature/land-use measurements, Bonan also analyzed a 100-year record of U.S. temperatures. Before 1940, when the two regions had more similar amounts of cropland, the difference in regional daily highs was much smaller than it is today. Since 1940, as agriculture continued to spread across the Midwest and northeastern farm lands returned to forests, the temperature difference steadily increased. The Northeast became warmer in the spring and summer as forests returned.

Bonan is currently using a computerized model of the climate to further investigate the impact of historical deforestation on the eastern United States. This project is funded by NASA's Earth Observing System.

The paper, "Observational Evidence for Reduction of Daily Maximum Temperature by Croplands in the Midwest United States," appears in the June 1 issue of the American Meteorological Society's Journal of Climate.

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Contact: Anatta
anatta@ucar.edu
303-497-8604
National Center for Atmospheric Research/University Corporation for Atmospheric Research
31-May-2001

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