Global assessment of water storage capacities in gray and green infrastructures across major river basins

Human-engineered “gray” infrastructure (e.g., artificial reservoirs) and ecosystem-based “green” infrastructure (e.g., forests) both provide essential water storage capacities to buffer hydrological variability under rising climate uncertainty. However, a quantitative assessment of gray ( S gray ) and green ( S green ) water storage capacities across global major river basins remains lacking. In this study, we estimate ecosystems’ root zone storage capacity as a proxy for S green using the mass curve technique. Combined with artificial reservoir storage capacities, our results showed that S gray and S green exhibit highly spatial heterogeneity, with the largest volumetric S gray in Yenisei (459 km 3 ) and S green in Amazon (1427 km 3 ). Over the period 1959–2020, S gray experienced a consistent increase, while S green exhibited fluctuations. Notably, in 12 % of the global major river basin area (1.3 × 10 7 km 2 ), including the Colorado, Yenisei, and Yangtze, indicating that human-engineered regulation of hydrology has become more influential than terrestrial ecosystem in these regions. These gray dominated basins are also projected to experience a decline in S green , suggesting the potential need to protect and enhance green infrastructure. This study provides a scientific basis for the integrated management of gray and green infrastructures, offering insights to enhance the resilience and sustainability of water resources at the basin scale.