August 14, 2007 -- By Sonal Noticewala, The New York Times
A fence built to prevent rabbits from entering the Australian outback has unintentionally allowed scientists to study the effects of land use on regional climates.
The rabbit-proof fence — or bunny fence — in Western Australia was completed in 1907 and stretches about 2,000 miles. It acts as a boundary separating native vegetation from farmland. Within the fence area, scientists have observed a strange phenomenon: above the native vegetation, the sky is rich in rain-producing clouds. But the sky on the farmland side is clear.
Researchers led by Tom Lyons of Murdoch University in Australia and Udaysankar S. Nair of the University of Alabama in Huntsville have come up with three possible explanations for this difference in cloudiness.
One theory is that the dark native vegetation absorbs and releases more heat into the atmosphere than the light-colored crops. These native plants release heat that combines with water vapor from the lower atmosphere, resulting in cloud formation.
Another hypothesis is that the warmer air on the native scrubland rises, creating a vacuum in the lower atmosphere that is then filled by cooler air from cropland across the fence. As a result, clouds form on the scrubland side.
A third idea is that a high concentration of aerosols — particles suspended in the atmosphere — on the agricultural side results in small water droplets and a decrease in the probability of rainfall. On the native landscape, the concentration of aerosols is lower, translating into larger droplets and more rainfall.
Within the last few decades, about 32 million acres of native vegetation have been converted to croplands west of the bunny fence. On the agricultural side of the fence, rainfall has been reduced by 20 percent since the 1970s.
Dr. Nair speculates that increases in the world’s population will prompt the clearing of more land to increase food production. But he wonders whether, in the long run, “we will reach a point of land clearing that will diminish food production,” because rainfall has decreased.
Dr. Lyons said he hoped the research would help scientists “understand the relationships between the land surface and atmosphere and to provide ideas for sustainable agricultural practices.”
The bunny fence, as it turns out, failed to prevent rabbits from entering the farmland, but it has successfully blocked kangaroos and emus.
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