Healthy freshwater ecosystems are essential for sustainable development. As human water use increases and hydrological processes change, the water available to ecosystems may become insufficient to meet their basic needs, leading to ecological water scarcity.
Ecological water scarcity occurs when the water available to ecosystems is insufficient in quantity or quality to sustain their structure, functions, and health. For a long time, water scarcity assessments have focused mainly on human water demand, with insufficient attention to whether enough water remains to sustain healthy ecosystems. To address this gap, the research team developed an indicator for assessing ecological water scarcity and applied it to 1,182 river basins worldwide.
In the 2000s, 412 of the 1,182 assessed river basins experienced ecological water scarcity, accounting for 35% of the total. Of all assessed basins, 17% experienced annual EWS and 18% experienced seasonal EWS. The affected areas covered about 37 million km2, equivalent to 29% of the study area, and accounted for nearly half of the global population.
Ecological water scarcity continued to expand over the past 150 years. From the 1850s to the 2000s, the area affected by ecological water scarcity grew by about 16 million km2. The expansion accelerated after the 1950s, when the affected area increased by about 10 million km2, accounting for 63% of the total expansion over the study period.
Human interventions are a major driver of global ecological water scarcity. In the 2000s, human interventions accounted for 53% of seasonal EWS cases and 60% of annual EWS cases. The effects of human intervention became more pronounced during the second half of the 20th century, directly intensifying EWS severity in about 13% of basins worldwide.
EWS risks are expected to persist in the future. By the 2050s, affected basins range from 392 under RCP2.6–SSP1 to 416 under RCP8.5–SSP5, with persistent hotspots in regions of intensive water use. These findings show that climate mitigation can reduce future EWS risk, but environmental flow protection, water-use efficiency, water recycling, ecologically informed infrastructure operation and ecosystem restoration are also needed to safeguard freshwater ecosystems.
The authors of the study include Junguo Liu and Hexin Lai from North China University of Water Resources and Electric Power, Bojie Fu from Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Mengru Wang from Wageningen University & Research, the Netherlands, and Peter H. Gleick from Pacific Institute, United States. The study was supported by the National Natural Science Foundation of China (42361144001), the 111 Project (D25014), the National Foreign Experts Program (Category S; S20240116), the Henan Provincial Key Laboratory of Hydrosphere and Watershed Water Security, the Henan Province Foreign Scientist Studio (GZS2024013), the Henan Provincial Talent Program (254000510004), and the Innovation Fund for doctoral of North China University of Water Resources and Electric Power (BCJJ202404). The work was also performed as part of the UNESCO Chair on Stepwise Ecological Restoration of Watersheds and the IAHS HELPING Working Group on Stepwise Ecological Restoration of Watersheds and on Acceptance of Nature-based Solutions & Their Implementation in Guidelines.
