People around the world depend on reservoirs for drinking water, hydropower, irrigation and more. These important sources of fresh water are affected by seasonal and long-term changes; the water in the reservoirs can dip during the hot summer months or due to prolonged drought, or flood after a very strong storm. Despite their importance, there are important gaps in our knowledge of storage structure and dynamics. Two recent papers use Landsat data to help fill in those gaps.
Researchers at the University of Southampton used Landsat data to determine where water levels advanced or receded from 1984 to 2022, creating the world’s first dataset that shows the exact year of permanent water changes—such as when a dam is formed or a stream dries up. The study can track changes in streams as narrow as 30m and lakes as small as 900m.2. In another study, Texas A&M University researchers used Landsat data to create a global bathymetry dataset called ‘3D-LAKES’ that enables water managers to estimate reservoir storage capacity.
The image above shows the Amistad Dam on the Texas-Mexico border. It uses a natural color Landsat image from 1985 overlaid on the Copernicus Digital Elevation Model (DEM) and bathymetric data from the 3D-LAKES dataset. Vertical relief is exaggerated by four points to highlight features of the topography and landscape. The reservoir is jointly managed by the US and Mexico through the International Boundary and Water Commission (IBWC) for flood control, recreation and hydroelectricity. Despite its importance in both countries, the dam is slowly shrinking. A table of surface water changes shows water levels have declined in recent decades, with a significant decrease between 2012 and 2016. The 3D-LAKES data table reveals the underwater structure of the reservoir. Together, these data complement in situ water level and condition data collected throughout the year.
Human settlements are created and shaped by water. We divert rivers, build dams and build artificial islands, while natural forces—hurricanes, raging rivers and rising seas—reshape our waterways and coastlines. With satellite data as an important tool for studying environmental dynamics, researchers have begun to build a more comprehensive global understanding of where water is and how it changes over time. In their studies of water change, the team at the University of Southampton focused on the permanent changes in lakes, rivers, coasts and other water bodies around the world.
Looking at long-term changes in the water surface can help scientists understand the drivers of change, said Gustavo Willy Nagel, lead researcher on the paper. Knowing when the lake began to decline helps water managers to investigate whether drought, irrigation or other forces caused the decline.
Scientists, policymakers, and water managers can explore the integrated data that Nagel and his team have created to visualize changes close to home as well as global impacts such as the drying of the Aral Sea, lakes created by melting glaciers in Tibet, and the construction of the Palm Islands in Dubai.
Assessing long-term changes in surface water presents a major challenge, as surface water is highly dynamic. The changing seasons and weather patterns mean that rivers, lakes and coastlines are constantly changing. To determine permanent water changes without including seasonal fluctuations, the researchers ran two algorithms. The first identified whether the water body is advancing or receding during the study period using the Modified Normalized Difference Water Index (mNDWI), which uses shortwave-infrared (SWIR) instead of near-infrared (NIR). The second algorithm used the Green_Red Normalized Difference Water Index (grNDWI) – an index developed by the research team – to determine the exact year that the body of water changed. A change was considered “permanent” if it did not return to its original level during the study period 1984 to 2022.
“Nagel shows, for each region of the world, the places where water has increased or decreased and the year of that change,” said Nagel.
Landsat can help us monitor surface water. But what about what under surface?
In a study published in Scientific information in October 2025, researchers from Texas A&M University combined Landsat and ICESat-2 data to create bathymetry maps for the world’s half a million lakes and reservoirs. The research team, led by Huilin Gao, used Landsat images to calculate the watershed, define where the water meets the land, and assess how the water level changes over time. Next, they combined laser altimetry from the ICESat-2 satellite to provide underwater bathymetry. With these measurements, scientists have developed spatial elevation relationships, which are an important metric for understanding how water storage changes with water levels.
The resulting dataset, called 3D-LAKES, is stable, as the bathymetry does not change much from year to year. “This data center can support many applications, from monitoring water storage to purifying water types,” said Chi-Hsiang Huang, lead author of the study.
3D-LAKES can be used in conjunction with Landsat-based maps—such as surface change surveys or the popular Global Surface Water dataset—to help water resource managers assess the volume of water held in a reservoir or lake. This allows them to assess flood risk, map habitat, or calculate how much water is available during a drought. Researchers can also track changes in water volume over time, helping to understand long-term water storage patterns.
Measuring groundwater levels in advance is expensive and impractical on a global scale. The 3D-LAKES database now provides researchers and managers with important bathymetry data for lakes and reservoirs around the world. “With this new dataset, we can achieve a comprehensive understanding of the impacts of lakes and reservoirs on regional climate, water security and ecosystem services,” Gao said. Both studies provide water and land managers with unprecedented resources for resource management and planning—from the Amistad Reservoir to the Australian Outback to the Brazilian Amazon.
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