NASA Reveals Earth's Rivers Change Less Over a Year Than Previously Thought

A space mission led by NASA and France has, for the first time, tracked how Earth's rivers swell and shrink throughout the year. The study found that the changes in river water levels were smaller than scientists had previously estimated using models. Researchers believe a record drought in the Amazon River region likely affected the results recorded by the Surface Water and Ocean Topography (SWOT) satellite, reported NASA.

The SWOT satellite was launched in 2022. This mission is being conducted in partnership with NASA and the French space agency CNES (Centre National d'Etudes Spatiales). It is the first satellite of its kind, designed to provide highly accurate studies of oceans as well as nearly all of the world's lakes and rivers.

Although SWOT does not directly measure the total water volume in rivers, it records changes in their width, surface elevation, and slope over time.

How The Satellite Measures Rivers

Previously, scientists relied primarily on computer-based models to estimate changes in water storage in rivers. They combined elevation data obtained from altimeters with width estimates derived from optical or radar data.

The SWOT satellite measures both river height and width simultaneously using its Ka-band Radar Interferometer instrument. This instrument sends microwave signals to the surface of the water and measures the time it takes for them to return. This provides scientists with detailed information about the state and changes in rivers.

A study published in the journal Nature analysed approximately 1.6 million satellite observations.

Key Findings Of The Study

The research examined approximately 127,000 river segments between October 2023 and September 2024. During this period, the total water volume in the rivers fluctuated by approximately 83 trillion gallons, or about 313 cubic kilometers.

This change was approximately 28 percent lower than previously estimated minimums. Scientists believe that the severe drought in the Amazon region during that period may be responsible for this difference. This region is considered to have the highest water volume in the world.

Despite the drought, the Amazon River recorded its highest fluctuations throughout the year. Its water level was observed to rise and fall by more than 45 trillion gallons. This amount is so great that it could cover the entire state of California with more than a foot of water.

Unexpected Results For The Nile River

The study also revealed a different pattern for the Nile, the world's longest river. Its water reserves changed by only about 2.2 trillion gallons over the course of the year, less than scientists had anticipated.

Researchers believe this may be due to dams built upstream, severe drought conditions, and initial challenges associated with using the new satellite instrument.

Initial Signals From The Mission

Cedric David, who leads the SWOT research team at the NASA Jet Propulsion Laboratory in Southern California, said the study offers an initial glimpse of the satellite's capabilities. He explained that scientists are now moving toward understanding the complex questions the SWOT mission was designed to address, and this research is only the beginning.

He also explained that river monitoring has long been challenging because many areas lack gauges and some river channels are so remote that surveys from boats or land are difficult. Many questions, such as the flow speed of rivers and how much water they receive from rain or melting snow, remain unclear.

Understanding Underwater River Structures

Monitoring river level fluctuations is also helping scientists understand the structure of river banks and river beds, which are often difficult to measure directly.

Study co-leader Arnaud Cerbelaud, a postdoctoral research fellow at the NASA Jet Propulsion Laboratory, explained that these structures impact many processes, from navigation to flood development. However, detailed maps of these underwater structures are still lacking in many parts of the world.