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July
2, 2007 For the first
time, scientists have used
satellite images to demonstrate a link between "The exciting thing is really for the first time, using a time series of satellite images, we can monitor Earth in a way that we haven't been able to," Seto said. "It's not just about urban growth or wetlands—it could be about desertification or deforestation—but it's really just this issue of human modification of the Earth." In one study, published in the July online issue of the
journal Global
Environmental Change, Seto and her colleagues showed that
inclusion in an
international environmental agreement did not significantly improve the
health
of a coastal mangrove habitat in a wetland preserve in Both findings are based on an analysis of satellite images of Urban growth in The Journal of Climate study focused on
the People's Republic of In a previous paper, Seto and her colleagues analyzed satellite imagery and found that urban areas in the Pearl River Delta increased more than 300 percent from 1988 to 1996. In the Journal of Climate study, the researchers compared this rapid urban growth with monthly temperature and precipitation data from 16 meteorological stations. Their analysis revealed a direct correlation between the rapid growth of cities and a decrease in rainfall during the winter dry seasons from 1988 to 1996. "We found that as the cities get bigger, there is a negative impact on precipitation patterns, such that in the winter season there is a reduction in rainfall as an effect of urbanization," Seto explained. "Primarily it is caused by the conversion of vegetated land to asphalt, roads and buildings. As a result, the soils have significantly less ability to absorb water, so in the winter months there is less moisture in the atmosphere and therefore a reduction in precipitation. We don't see the same impact in summer months, in part because the effect of the Asian monsoon masks the effect of urbanization." "When cities are still relatively small, we don't see this
pattern
emerging," she added. "It happens when cities get very large. But
that's the part that I think is alarming, because we see large-scale
city
development all over Coastal changes in In the Global Environmental Change study,
the researchers focused on The growth of aquaculture in recent years has threatened coastal mangrove forest habitats in the Red River Delta. In response, the Vietnamese government has established protected areas, such as the Xuan Thuy Natural Wetland Reserve, which was designated a Ramsar site in 1988. For the study, Seto and her colleagues concentrated on Xuan Thuy and a nearby reserve that is not included in the Ramsar treaty. The researchers analyzed a series of Landsat images taken between 1975 and 2002. Analysis revealed that both reserves experienced increased fragmentation of mangrove forest habitat with increased aquaculture. Contrary to expectations, the scientists found that aquaculture developed at a faster rate at the Xuan Thuy treaty site than at its non-Ramsar neighbor. These findings mirrored statements by local residents in 2001, when Seto and her co-workers interviewed one-third of the households living and farming within the boundaries of both reserves. The researchers were told that aquaculture had been ongoing in the region since the early 1980s. These results showed that satellite technology is a cost-effective means of assessing wetland health, Seto said, noting that the cost of acquiring the satellite images and conducting the interviews in the field totaled less than $5,000. This technique could be used to verify compliance with other
environmental
agreements, added Ron Mitchell, professor of public policy at the Other co-authors of the Journal of Climate
study are Robert Kaufmann
of The Global Environmental Change study was co-authored by Michail Fragkias of the International Human Dimensions Programme on Global Environmental Change and was supported by NASA, NSF and a National Geographic Research Grant. ## Recommend this Article to a Friend Back to: News |
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