How to measure green water scarcity

Joep Schyns, Arjen Hoekstra and Martijn Booij

What is green water? No, it is not water that is green of color. It is normal freshwater, but in a specific part of the hydrological cycle. Green water refers to the precipitation on land that does not run off or recharge the groundwater but is stored in the soil or temporarily stays on top of the soil or vegetation. Eventually, this water returns to the atmosphere through evapotranspiration from the soil and vegetation.

Green water is the major source of water for agriculture, forestry and terrestrial ecosystems. However, research and debate on water scarcity have been mainly focused on water in rivers and underground – so-called blue water – and not on green water.

In a new article Schyns, Hoekstra and Booij (2015) discuss the multiple dimensions of water scarcity and draw attention to the fact that green water is also a scarce resource, because its availability is limited and there are competing demands for green water. The article reviews how green water scarcity can be measured and how it relates to concepts such as aridity and drought.