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January 22nd, 2020

Shaped by humans, river deltas are gaining land worldwide—for now

A new study of nearly every delta on the planet shows how river delta shapes and sizes around the world are changing due to human activity. The study, carried out by a team of Dutch and American researchers that includes INSTAAR Albert Kettner, finds that increased soil erosion from deforestation has been building land in deltas over the past 30 years, despite extensive river damming. This trend is likely to reverse as sea-level rise accelerates and other human impacts take effect.

Populated by hundreds of millions of people, river deltas are among the most economically and ecologically valuable environments on Earth. People living on deltas, however, are increasingly vulnerable to sea-level rise and coastal hazards such as major storms, extremely high tides, and tsunamis. Many deltas experience a decline in sediment supply due to upstream damming, making them even more vulnerable. However, large scale upstream deforestation resulting in soil erosion has increased the amount of sediment that is transported to many deltas, including many in Southeast Asia.

The new paper, published today in Nature, considers about 11,000 deltas worldwide and takes advantage of the wealth of information available from global datasets on river drainage basins, sediment fluxes, and tidal range, among others. The authors developed a model to predict how the shapes of deltas change as factors like waves, tides, river flow, damming, and deforestation affect how much sediment travels down rivers to the deltas.

Authors of the study are from Utrecht University, Woods Hole Oceanographic Institution, Indiana University, Wageningen University, CU Boulder, Los Alamos National Laboratory, and Tulane University. The study was funded through the National Science Foundation (NSF-EAR-GLD).

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