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Urban sprawl curbs food production, study shows
Urban sprawl limits the ability of the land to take carbon dioxide out of the atmosphere and convert it to biomass, researchers conclude from an analysis of satellite imagery.
"Humans tend to congregate where the best resources are," said Marc Imhoff, a researcher at the Goddard Space Flight Center in Greenbelt, Maryland. "Is it wise to take the best soils and turn them into parking lots?"
To find out, Imhoff and his colleagues took satellite imagery of city lights, which serve as a measure of urban sprawl, and combined it with data from another satellite that records the photosynthetic potential of the landscape.
"By merging the satellite data we could examine how urbanization affects the potential of the land surface to carry out photosynthesis by looking at the 'greenness' index inside and outside the urbanized area," he said.
It turns out that urban sprawl can reduce the photosynthetic ability of land by as much as 20 days in areas where construction is particularly dense. Put another way, said Imhoff, the effect is like turning out the lights in a greenhouse for 20 days.
With only 3 percent of the land in the United States covered by urban development and ample arable land yet untapped, urban sprawl does not yet pose a significant threat to the nation's food supply.
"In countries like Egypt, where there is not much arable land and all the urbanization is taking place along the Nile River, in terms of local food supply it is a serious issue," said Imhoff.
However, the study also showed that human activity could increase productivity by altering the environment. "For example, this was the case for arid and semi-arid areas where lawn irrigation and planting changed the ecosystems from shrub lands and desert to deciduous forests," said Imhoff.
Since human survival depends on photosynthesis, the researchers hope urban planners will find the study useful. Imhoff suggests that cities should be built on poorer soils, even though construction costs might be bit higher.
"As population increases we are going to have to rely on our soil resources more and more," said Imhoff. "Because of their style of consumption, in Europe the amount of land needed to support urban areas is 100 times larger than the urban area itself."
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Satellite images show effects of urban sprawl
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