Trends in freshwater availability across the globe are reported in a paper published this week in Nature. Understanding trends in water storage on land is crucial for managing human and ecological sustainability.

Freshwater availability is changing worldwide, but assessing these changes on a global scale is exceedingly difficult. Much of our knowledge comes from a limited set of ground-based, on-site observations, which can be expensive, and does not provide a complete evaluation of freshwater availability.

Matthew Rodell and colleagues analyse the 2002-2016 record of terrestrial water storage, provided by the GRACE gravity-measuring satellite. The data reveal areas of both strong increases and decreases in water storage, sometimes in neighbouring regions. The authors find that several of these trends have heretofore lacked thorough investigation and attribution, including those evidencing massive changes in northwestern China and the Okavango Delta in Botswana, whereas others are consistent with climate model predictions. The findings reveal that change in any one area reflects the integrated impacts of natural climate variability and human activities, suggesting the need for a joint approach of water management within and among nations. This observation-based assessment of how the world’s water supply is responding to human impacts and climate variations provides a blueprint for evaluating and predicting emerging threats to water and food security.