New method combines measurements of river levels with computer models to provide a comprehensive view of the amount of water in rivers and rates of flow to the oceans
A recent study led by NASA researchers provides new estimates of the volume of water flowing in Earth’s rivers, the rates of flow to the oceans, and how this data changes over time.
This information is critical to understanding the planet’s water cycle and managing its freshwater resources.
The study, recently published in the journal Nature Geoscience, also highlights regions where intense human use of water has left its mark, such as the Colorado River basin in the United States, the Amazon basin in South America and the Orange River in Southern Africa.
For the study, researchers at NASA’s Jet Propulsion Laboratory in Southern California used an innovative method that combines measurements of river levels with computer models of about 3 million river segments worldwide.
The results show that the total volume of water in Earth’s rivers, on average from 1980 to 2009, was 539 cubic miles (2,246 cubic kilometers).
This amount is equivalent to half the water volume of Lake Michigan and represents approximately 0.006% of all freshwater, which in turn makes up 2.5% of the global volume.
Despite their small proportion of the planet’s total water, rivers have been vital to humans since the earliest civilizations.
The new method allowed us to estimate that the Amazon basin contains approximately 38% of the world’s river water, the highest percentage of all the hydrological regions examined.
While numerous estimates have been made over the years of the flow of water from rivers to oceans, estimates of the overall volume of water held in rivers, known as “storage,” have been few and more uncertain, according to Cédric David of JPL , co-author of the study.
He likened the situation to spending money from a checking account without knowing the balance. “We don’t know how much water is in the bill, and population growth and climate change are complicating matters further“said David. “There are many things we can do to manage our water use and make sure there is enough for everyone, but the first question is: how much water is there? This is fundamental to everything else“.
The estimates provided in the study could in the future be compared with data from the international Surface Water and Ocean Topography (SWOT) satellite to improve measurements of human impact on the Earth’s water cycle.
Launched in December 2022, SWOT maps water elevations around the world, and changes in river heights offer a way to quantify storage and runoff.
The study identified the Amazon basin as the region with the largest amount of water stored in rivers, at about 204 cubic miles (850 cubic kilometers), or 38% of the global estimate.
The same basin also discharges the largest amount of water into the oceans: 1,629 cubic miles (6,789 cubic kilometers) per year.
This figure represents 18% of global runoff to the oceans, which averaged 8,975 cubic miles (37,411 cubic kilometers) per year from 1980 to 2009.
The study also identified areas where intense human use of water has left a significant footprint, such as parts of the Colorado, Amazon, Orange and Murray-Darling river basins.
In these areas, the amount of water leaving the river segments is less than that entering, which generally indicates intense abstraction by humans. “These are the locations where we are seeing the fingerprints of water management“ said Elyssa Collins, lead author of the study, who conducted the analysis as an intern at JPL and a doctoral student at North Carolina State University in Raleigh.
The new study provides a more complete and accurate view of how much water is in Earth’s rivers and how this vital resource is used and affected by human activities.
The findings could have important implications for water management and future planning in an increasingly thirsty world.
Source and original article: https://go.nasa.gov/3xQO3WY
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