The loss of reservoir capacity poses significant risks to water supplies for over 2 billion people and threatens more than a quarter of global irrigated land. Sediment build-up also endangers dam safety and disrupts downstream ecosystems. Arid regions, such as Namibia and parts of Australia, face the highest risks, with nearly all reservoirs in these areas projected to become non-functional. The study warns that these challenges will be exacerbated by climate change and population growth, further straining water resources.