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September 20th, 2009

World’s river deltas sinking due to human activity

James Syvitski, Albert Kettner, Irina Overeem, Eric Hutton and Mark Hannon, along with colleagues from six other institutions, have shown that most of the world's low-lying river deltas are sinking from human activity, making them increasingly vulnerable to flooding from rivers and ocean storms and putting tens of millions of people at risk. The authors first chose 33 major deltas to represent those of the world. For each delta, the team then carefully examined high-resolution satellite images, Shuttle radar topopography, historical maps, river sediment load records, and sea level data. They found that 24 out of the world's 33 major deltas are sinking and that 85 percent experienced severe flooding in recent years.

While the 2007 Intergovernmental Panel on Climate Change report concluded many river deltas are at risk from sea level rise, the new study indicates other human factors are causing deltas to sink significantly. The researchers discovered that the sinking of deltas from Asia and India to the Americas is exacerbated by the upstream trapping of sediments by reservoirs and dams, man-made channels and levees that whisk sediment into the oceans beyond coastal floodplains, and the accelerated compacting of floodplain sediment caused by the extraction of groundwater and natural gas.

Published in the Sept. 20 issue of Nature Geoscience, the study was led by James Syvitski, who is directing a $4.2 million effort funded by the National Science Foundation to model large-scale global processes on Earth like erosion and flooding. Known as the Community Surface Dynamic Modeling System, or CSDMS, the effort involves hundreds of scientists from dozens of federal labs and universities around the nation.

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