A study led by NASA researchers provides new estimates of the amount of water flowing through Earth’s rivers, the speed at which it flows into the ocean and the fluctuations of both figures over time.
This information is crucial to understanding the planet’s water cycle and managing its freshwater reserves.
The results also highlight regions depleted by intensive water usesuch as the Colorado River Basin in the United States, the Amazon Basin in South America, and the Orange River Basin in southern Africa.
The volume of water that flows through the planet’s rivers
For the study, which has just been published in Nature Geoscienceresearchers at NASA’s Jet Propulsion Laboratory used a novel methodology that combines flowmeter measurements with computer models of some 3 million river segments around the world.
Scientists estimate that the total volume of water in Earth’s rivers between 1980 and 2009 was, on average, 2,246 cubic kilometers. This is equivalent to half the water in Lake Michigan and approximately 0.006% of all freshwater, which is 2.5% of the world’s volume.
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“Fingerprints” of water use
The study identified the Amazon basin as the region with the largest river storage, with about 850 cubic kilometers of water, approximately 38% of the global estimate. The same basin is also the one that discharges the most water into the ocean: 6,789 cubic kilometers per year. This represents 18% of global discharge into the ocean, which reached an average of 37,411 cubic kilometers annually between 1980 and 2009.
Although it is not possible for a river to have a negative discharge (the study’s approach does not take into account upstream flow), It is possible that in some segments of the river less water leaves than enters. That’s what researchers found in parts of the Colorado, Amazon and Orange river basins, as well as the Murray-Darling basin in southeastern Australia. These negative flows indicate, above all, intense human use of water..
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“In these places we see the traces of water management”says lead author Elyssa Collins, who conducted the analysis as a JPL fellow and doctoral student at North Carolina State University in Raleigh.
Knowing how much water there is is essential for everything else
Although researchers have made numerous estimates over the years of the amount of water flowing from rivers to the ocean, estimates of the volume of water that rivers collectively retain (known as storage) have been few and more uncertainsaid Cédric David of JPL, co-author of the study.
David compared the situation to spending money from a checking account without knowing the balance. “We don’t know how much water is in the account, and population growth and climate change complicate things even more”David said. “There are a lot of things we can do to manage how we’re using it and make sure there’s enough water for everyone, but the first question is: How much water is there? That’s critical to everything else.”
News reference:
Collins, EL, David, C.H., Riggs, R. et al. Global patterns in river water storage dependent on residence time. Nat. Geosci. (2024). ttps://doi.org/10.1038/s41561-024-01421-5
