Green water: Recycling water resources within the ecosystem-atmosphere network [version 2]

Green water, temporarily stored in the unsaturated zone of the soil or on the top of vegetation, plays an important role in the natural water cycle and water resource management. Unlike surface water flows, green water recycling has no obvious boundary restrictions and is characterized by long-distance transport. Thus, green water from specific basins can support precipitation not only within the basin but also in neighboring basins and even distant areas. However, water scarcity is typically viewed as a local problem for which management measures at the basin scale seem sufficient without fully considering the interdependence of green water among basins. Limited knowledge of green water recycling could make hydrological water assessments inaccurate. Here, we quantify the global green water recycling network, which links green water as a moisture supply to precipitation and thus contributes to local and remote freshwater resources. Our results show that large basins such as the Congo (green water recycling ratio: 56.6%) are comparatively independent, but still rely to some extent on moisture supplied by other basins (contributing 21.4% of precipitation for the Congo), contradicting the conventional view of basin independence in water management. This illustration of basin interdependence highlights the need for global water governance in the context of the severe global water crisis, and this global green water recycling network provides the basis for a comprehensive assessment of water resources and scarcity under global change.