Reservoir sedimentation threatens billions with growing water risk

More than half of all global reservoirs could become functionally inoperable by 2060 due to sedimentation, threatening water supplies to over 2 billion people and impacting more than 26 per cent of global irrigated land across 16 global high-sedimentation hotspots, a new study has warned.

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. There is an urgent need for targeted, nature-based sediment management, particularly in dryland regions, where small reservoirs are critical for domestic water access and food production, the study led by professor Song Chunqiao of the Nanjing Institute of Geography and Limnology (NIGLAS) of the Chinese Academy of Sciences, said.

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 per cent of these reservoirs are smaller than one square kilometer – a category largely absent from previous assessments.

Reservoir sedimentation is an escalating threat to global water security, the study noted, adding that of the projected inoperable reservoirs by 2060, 58.6 per cent are small one while 38.1 per cent are large reservoirs.

“This study provides the first high-resolution global assessment of reservoir sedimentation that fully incorporates small reservoirs”, Liu Kai, first author of the study and a researcher at NIGLAS.

“Reservoirs play a key role in daily life. They provide water for farming, drinking, flood control, and electricity. But over time, soil and sand carried by rivers build up behind dams, a process called sedimentation. This buildup reduces the space available for water, making the reservoirs less useful,” Liu explained.

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 identified 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 two 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.”