Reservoirs around the world are losing storage capacity at an average rate of 7.3 percent per decade—disproportionately affecting small reservoirs, which together provide water to billions of people.
The data come from a study published in Nature Sustainability on June 5, which offers the clearest global assessment of reservoir sedimentation to date.
In the study, led by Prof. SONG Chunqiao of the Nanjing Institute of Geography and Limnology (NIGLAS) of the Chinese Academy of Sciences, the researchers developed the Global REservoir Inventory (GREI), combining remote sensing, geospatial data, and engineering records to identify more than 550,000 reservoirs worldwide. Over 95 percent of these reservoirs are smaller than one square kilometer—a category largely absent from previous assessments.
"This study provides the first high-resolution global assessment of reservoir sedimentation that fully incorporates small reservoirs," said LIU Kai, first author of the study and a researcher at NIGLAS.
Reservoirs are essential infrastructure for flood control, irrigation, water supply, and hydropower generation. However, sediment trapped behind dams gradually reduces usable storage capacity, weakening reservoir functionality and threatening long-term water security. Reduced downstream sediment transport may also alter river morphology and intensify risks such as delta subsidence, coastal erosion, and ecosystem degradation.
Using field-based sedimentation observations from more than 6,000 reservoirs and a physics-guided machine learning framework, the team found that nearly one in five reservoirs already faces rapid storage loss. Small reservoirs are particularly vulnerable, especially in dryland regions such as the southwestern United States, the Middle East, and western Australia.
The study also identifies 16 global sedimentation hotspots, many of which overlap with major irrigated agricultural regions and water-scarce drylands.
The researchers found that around one-quarter of global irrigated land, affecting more than 2 billion people, is exposed to elevated sedimentation risk, raising concerns for long-term water and food security. Without effective intervention, the study estimates that more than half of global reservoirs could experience functional degradation by 2060.
"Reservoir sedimentation deserves greater attention as a growing challenge to long-term water, food, and energy security," Prof. SONG said. "More sustainable reservoir management will be essential for supporting human well-being and advancing global sustainable development."
