NASA decodes the flow of Earth’s rivers: new revelations

NASA decodes the flow of Earth’s rivers: new revelations
NASA decodes the flow of Earth’s rivers: new revelations

A NASA-led study combined gauging measurements with computer models of 3 million river segments to create a global picture of how much water Earth’s rivers contain. The Amazon basin is estimated to contain approximately 38% of the world’s river water, the largest portion of all hydrological regions assessed. Credit: NASA

NASA Scientists have developed a new method to accurately measure the volume and flow of water in Earth’s rivers, revealing critical data for water management. Their research shows that rivers contain a small fraction of the planet’s fresh water, with the Amazon basin alone accounting for almost 40% of this volume and leading the oceans’ discharge rates.

For decades, most estimates of total river water on Earth were improvements on a 1974 United Nations figure. It has been difficult to obtain better estimates due to the lack of observations of the world’s rivers, particularly those far from human populations. Now, using a new approach, NASA scientists have made new estimates of how much water flows through Earth’s rivers, how fast it flows into the ocean, and how much of these two figures over time. This information is crucial for understanding the planet’s water cycle and managing its freshwater reserves.

To get a global picture of how much water is held by Earth’s rivers, scientists at NASA’s Jet Propulsion Laboratory (JPL) combined gauging measurements with computer models of about 3 million river segments worldwide. The research was led by Elyssa Collins, who conducted the analysis as JPL intern and doctoral student at North Carolina State University, and was published in the journal Natural geosciences.

Scientists have estimated that the total volume of water in Earth’s rivers, on average, between 1980 and 2009, was 2,246 cubic kilometers (539 cubic miles). This is equivalent to half of Lake Michigan’s water and about 0.006 percent of all fresh water, representing 2.5 percent of the world’s total water volume. Despite their small proportion of the planet’s water, rivers have been vital to humans since the first civilizations.

The NASA-led study estimated the flow of 3 million river segments, identifying locations around the world with intense human water use, including parts of the Colorado River basins, Amazon, Orange and Murray-Darling, shown in gray here. Credit: NASA

The map at the top of this page shows the volume of water stored by hydrological region. The researchers estimated that the Amazon basin (darkest blue) contains about 38 percent of the world’s river water, the largest portion of any hydrological region assessed. The same basin also releases the most water into the ocean (second map): 6,789 cubic kilometers (1,629 cubic miles) per year. This represents 18% of global discharges into the ocean, which averaged 37,411 cubic kilometers (8,975 cubic miles) per year from 1980 to 2009.

Although it is not possible for a river to have negative flow (the study approach does not allow for upstream flow), for accounting reasons it is possible that less water flows out of some segments of river than it enters. This is what the researchers discovered. for parts of the Colorado, Amazon and Orange river basins, as well as the Murray-Darling basin in south-eastern Australia. These negative flows mostly indicate intense human water use.

“These are places,” Collins said, “where we see the fingerprints of water management. »

To learn more about this research, see New global accounting of Earth’s rivers reveals ‘fingerprints’ of intense water use.

NASA Earth Observatory images by Lauren Dauphin, using data from Collins, EL et al. (2024). The text was adapted from material first published on April 24, 2024 by Andrew Wang/JPL.

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