Satellite Imaging -Urban Growth is Changing the World’s Rainfall Patterns

“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,” say Karen Seto, assistant professor of geological and environmental sciences and a fellow at the Woods Institute for the Environment at Stanford University 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.”

These new findings are based on an analysis of satellite images of Vietnam and China, which NASA has been collecting through its Land Remote-Sensing Satellite (Landsat) Program for more than 30 years.

“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 China and throughout the developing world.”

These discoveries also suggest that satellite imaging could help verify regional compliance (or noncompliance) with environmental agreements. Ron Mitchell, professor of public policy at the University of Oregon and an expert on multi-national environmental treaties, believes that remote sensing will be a valuable tool in evaluating climate change agreements.

“Too often in the past policymakers have been at a loss as to how to evaluate progress,” he said. “Remote sensing could be used to evaluate many international environmental agreements, particularly habitat-based conventions…deforestation, desertification and carbon sequestration projects under a climate change agreement.”

Posted by Rebecca Sato

Stanford University Link

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