Researchers at NASA's Jet Propulsion Laboratory in Southern California have determined that the average global river water volume from 1980 to 2009 was about 539 cubic miles (2,246 cubic kilometers). This volume is roughly equivalent to half of Lake Michigan's water capacity and represents a mere 0.006% of all freshwater, which totals 2.5% of the Earth's water volume. Despite their small percentage, rivers are critical to human civilization from the earliest times.
JPL's Cedric David, a co-author of the study, discussed the historical challenges in quantifying river storage and flow: "Although researchers have made numerous estimates over the years of how much water flows from rivers into the ocean, estimates of the volume of water rivers collectively hold - known as storage - have been few and more uncertain," David said. He compared the situation to "spending from a checking account without knowing the balance." He added, "We don't know how much water is in the account, and population growth and climate change are further complicating matters. There are many things we can do to manage how we're using it and make sure there is enough water for everyone, but the first question is: How much water is there? That's fundamental to everything else."
The study further anticipates that these estimates could soon be refined and expanded with data from the Surface Water and Ocean Topography (SWOT) satellite, which was launched in December 2022. SWOT is tasked with mapping global water elevations and could significantly enhance the precision of measurements concerning human impacts on the water cycle, including storage and discharge assessments.
The research highlights several key regions with notable water storage and depletion due to human activity. The Amazon basin emerged as the area with the highest river storage, holding approximately 204 cubic miles (850 cubic kilometers) of water, around 38% of the global total. It also discharges the most water into the ocean, averaging 1,629 cubic miles (6,789 cubic kilometers) annually. However, the study also pointed out areas where water outflow is less than the inflow, such as parts of the Colorado, Amazon, and Orange River basins, indicating heavy human water use.
Lead author Elyssa Collins, who conducted the analysis while a JPL intern and doctoral student at North Carolina State University, commented on the methodology and findings. "These are locations where we're seeing fingerprints of water management," she said.
In pursuit of a better understanding of river water dynamics, the researchers combined data from gauge measurements with simulations from three different land surface models to reconcile discrepancies between observed and estimated water flows. This allowed them to create a high-resolution global map of rivers using elevation data and satellite imagery, including from NASA's Shuttle Radar Topography Mission.
Elyssa Collins, now a postdoctoral researcher at the University of North Carolina at Chapel Hill, emphasized the importance of the new approach. "That way we can see where in the world the most amount of river water is stored, or where the most amount of water is being emptied into oceans from rivers," she explained.
Research Report:Global patterns in river water storage dependent on residence time
Related Links
Surface Water and Ocean Topography
Water News - Science, Technology and Politics
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
