New NASA-French Satellite Tracks Global River Fluctuations

SWOT mission finds less dramatic seasonal swings in river volumes than previous estimates

Published on Mar. 4, 2026

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A new study using data from the NASA-CNES Surface Water and Ocean Topography (SWOT) satellite has revealed that the seasonal fluctuations in global river volumes are significantly less dramatic than previously thought. The satellite's precise measurements of river height and width over the course of a year found about 28% less variation in river volumes compared to the lowest previous estimates. The findings also provided new insights into the underwater topography of river channels around the world.

Why it matters

Understanding the seasonal changes in river volumes is crucial for managing water resources, predicting floods and droughts, and modeling the global water cycle. Previous estimates relied on models or indirect measurements, but the SWOT satellite is the first to directly observe these changes across nearly all the world's rivers. The new data challenges assumptions and will help improve hydrological models and forecasting.

The details

The SWOT satellite, a collaboration between NASA and the French space agency CNES, tracked the height, width, and slope of 127,000 river segments over the course of a year from October 2023 to September 2024. In total, the world's rivers varied in volume by about 83 trillion gallons (313 cubic kilometers) during that period, 28% less than the lowest previous estimates. The Amazon River, the world's largest by volume, experienced the greatest seasonal fluctuations, gaining and losing 45 trillion gallons (172 cubic kilometers). In contrast, the Nile River varied by only 2.2 trillion gallons (8.5 cubic kilometers), likely due to upstream damming and drought. The new data also revealed previously unmapped details about the shape and topography of river channels around the world.

  • The SWOT satellite was launched in December 2022 and is now in its operations phase, collecting data.
  • The study analyzed observations from October 2023 to September 2024.

The players

SWOT

The Surface Water and Ocean Topography (SWOT) satellite is a collaboration between NASA and the French space agency CNES, with contributions from the Canadian Space Agency and UK Space Agency. It is the first satellite capable of surveying nearly all the world's lakes and rivers with ultraprecision.

Cedric David

The lead of the SWOT research team that conducted the study at NASA's Jet Propulsion Laboratory.

Arnaud Cerbelaud

A postdoctoral research fellow at JPL who co-led the study on SWOT's river observations.

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What they’re saying

“We're starting to untangle some of the really tough questions SWOT was built for. This is just the beginning.”

— Cedric David, Lead of the SWOT research team (NASA)

“The implications go far beyond hydrology and will help us understand how water moves through the global Earth system.”

— Arnaud Cerbelaud, Postdoctoral research fellow (NASA)

What’s next

The SWOT team plans to continue analyzing the satellite's data to further refine our understanding of global river dynamics and their role in the Earth's water cycle.

The takeaway

The new SWOT satellite data is challenging previous assumptions about the seasonal fluctuations in river volumes, providing a more accurate picture that will help improve water resource management and hydrological modeling around the world.