Shifting water scarcities: irrigation alleviates agricultural green water deficits while increasing blue water scarcity

Abstract

Agricultural areas often experience green water scarcity-the limitation of crop growth by soil moisture supplied through rainfall and snowmelt-due to e.g. unfavourable soil texture, high potential evapotranspiration rates, poor or inefficient crop management, and fluctuations in meteorological conditions. Driven by the growing effects of climate change and the rising water and food demands of an increasing world population, agricultural green water scarcity is becoming an increasingly important phenomenon. In this global modelling study, a plant-physiology based indicator of green water stress is applied, that quantifies the ratio between soil moisture limitation and atmospheric water demand on agricultural areas. Results show that currently (2015–2019 average) 44 % (686 Mha) of the global agricultural area is green water stressed. Hotspots are characterized by a high seasonal variability in stress conditions, and are mainly located in India and Pakistan, northern Sub-Saharan Africa, North Africa and southwestern Asia. Using an analogous blue water stress indicator-which relates human water use for households, industry and agriculture to available blue water resources-current irrigation is shown to alleviate plant water stress in agricultural areas by compensating for green water scarcity on 8 % (140 Mha) of the total agricultural area, but simultaneously increases the share of areas experiencing blue water stress by 6 % (96 Mha). This shift in water stress types highlights the importance of jointly considering the interconnected green and blue water resources and stresses in pathways towards sustainable water use in agriculture.