How much water is stored in the world’s river systems and how much is discharged to oceans? Data from stream-gauge monitors were combined with computer models of about 3 million river segments to assess such water cycle trends.

Stream gauge measurements reflecting runoff flowing into and through a river system were used as input to model runoff through rivers on a high-resolution global map developed using land-elevation data and imagery from space. The resulting discharge rates were then used to estimate average and monthly storage for individual rivers and the Earth’s rivers in total.

The total volume of water in rivers on average for the 1980 to 2009 period was determined to be equivalent to 539 cubic miles (2,246 cubic kilometers). The most river storage was assigned to the Amazon basin, holding about 204 cubic miles (850 cubic kilometers) of water, or 38% of the global estimate. This basin is also responsible for 18% of global discharge to the ocean: 1,629 cubic miles (6,789 cubic kilometers) per year.

Adverse impacts of intensive water use in some regions were evident in terms of negative discharge trends. Areas depleted by heavy water use include parts of the Colorado, Amazon and Orange river basins, as well as the Murray-Darling basin in southeastern Australia.

Researchers from NASA Jet Propulsion Laboratory, Texas A&M University, Virginia Polytechnic Institute and State University, University of North Carolina, Peking University (China), University of California San Diego, University of Tokyo (Japan) and North Carolina State University contributed to this study, which is published in Nature Geoscience.

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