A sweeping new global study finds that reservoir sedimentation is quietly eroding water security for billions of people, with small reservoirs — largely overlooked until now — facing the steepest risks. More than half of all reservoirs worldwide could be functionally degraded by 2060.
Reservoirs are quietly losing their ability to store water — and the problem is far more widespread than scientists previously understood. A study published June 5 in Nature Sustainability offers the most comprehensive global look yet at reservoir sedimentation, revealing that storage capacity is shrinking at an average rate of 7.3% per decade and that smaller reservoirs, which collectively serve billions of people, are bearing the brunt of the damage.
A Database Built From Half a Million Reservoirs
The research was led by Chunqiao Song, a professor at the Nanjing Institute of Geography and Limnology (NIGLAS), part of the Chinese Academy of Sciences. To conduct the study, the team built a new resource called the Global REservoir Inventory (GREI), drawing on satellite remote sensing, geospatial databases and engineering records to catalog more than 550,000 reservoirs around the world. More than 95% of those reservoirs measure smaller than one square kilometer — a class of water infrastructure that has largely been left out of prior large-scale analyses.
That gap matters enormously. Small reservoirs are often the primary or sole water source for rural and semi-arid communities, yet they have historically flown under the radar of global water security assessments.
“This study provides the first high-resolution global assessment of reservoir sedimentation that fully incorporates small reservoirs,” first author Kai Liu, a researcher at NIGLAS, said in a news release.
To estimate sedimentation rates across such a large and diverse dataset, the team combined field-based observations from more than 6,000 reservoirs with a physics-guided machine learning framework. This approach allowed researchers to draw on real-world measurements while extending predictions to reservoirs where direct data are unavailable — a methodological advance that gives the findings much broader scope than earlier studies.
Nearly One in Five Reservoirs Faces Rapid Storage Loss
The results paint a troubling picture. Roughly one in five reservoirs is already experiencing rapid storage loss due to accumulated sediment. When rivers flow into reservoirs, they carry fine particles of sand, silt and clay that gradually settle on the reservoir floor, reducing the volume of water that can be stored. Over time, this process — known as sedimentation — can render a reservoir unable to fulfill its intended purpose, whether that is flood control, irrigation, drinking water supply, or hydropower generation.
Small reservoirs in dryland regions are especially vulnerable. The study singles out the southwestern United States, the Middle East and western Australia as areas of particular concern, where reservoirs already operate under water stress and have less redundancy to absorb losses in storage capacity. The researchers identified 16 global sedimentation hotspots, many of which coincide with heavily irrigated agricultural zones — a worrying overlap that amplifies the threat to food production.
Why It Matters for Water, Food and Energy
The implications extend well beyond water availability. The study estimates that roughly one-quarter of all irrigated farmland worldwide is exposed to elevated sedimentation risk, affecting more than 2 billion people who depend on those crops and water systems. Irrigation is the backbone of global food production, and as reservoir capacity shrinks, farmers face increasingly unreliable water supplies during dry seasons and droughts.
The consequences don’t stop at the reservoir’s edge, either. When dams trap sediment, less of it travels downstream. That reduction can reshape river channels, accelerate coastal erosion, contribute to delta subsidence, and degrade freshwater and coastal ecosystems — a cascade of environmental effects that researchers are only beginning to quantify at a global scale.
Without meaningful intervention, the study projects that more than half of the world’s reservoirs could experience functional degradation by 2060.
“Reservoir sedimentation deserves greater attention as a growing challenge to long-term water, food, and energy security,” added Song. “More sustainable reservoir management will be essential for supporting human well-being and advancing global sustainable development.”
What Can Be Done?
The study does not simply issue a warning — it also serves as a diagnostic tool. By mapping sedimentation risk at high resolution and flagging specific hotspot regions, the GREI database can help governments and water managers prioritize maintenance, sediment flushing operations, and long-term reservoir design improvements. Techniques such as controlled sediment flushing — already practiced at large installations like China’s Xiaolangdi Reservoir — can help preserve storage capacity when applied regularly, though scaling such approaches to hundreds of thousands of small reservoirs worldwide presents a formidable challenge.
For college students studying environmental science, civil engineering, public policy or international development, the findings underscore a critical but underappreciated area of infrastructure risk. Water security is inseparable from food security and energy production, and the physical decay of reservoir infrastructure could become one of the defining resource challenges of the coming decades — particularly in regions already strained by climate variability and population growth.
Source: Chinese Academy of Sciences