Global consumptive water use for crop production: The importance of green water and virtual water

Over the last 4 decades the use of blue water has received increasing attention in water resources research, but little attention has been paid to the quantification of green water in food production and food trade. In this paper, we estimate both the blue and green water components of consumptive water use (CWU) for a wide range of agricultural crops, including seven cereal crops, cassava, cotton, groundnuts, potatoes, pulses, rapeseed, soybeans, sugar beets, sugarcane, and sunflower, with a spatial resolution of 30 arc min on the land surface. The results show that the global CWU of these crops amounted to 3823 km3 a−1 for the period 1998–2002. More than 80% of this amount was from green water. Around 94% of the world crop‐related virtual water trade has its origin in green water, which generally constitutes a low‐opportunity cost of green water as opposed to blue water. High levels of net virtual water import (NVWI) generally occur in countries with low CWU on a per capita basis, where a virtual water strategy is an attractive water management option to compensate for domestic water shortage for food production. NVWI is constrained by income; low‐income countries generally have a low level of NVWI. Strengthening low‐income countries economically will allow them to develop a virtual water strategy to mitigate malnutrition of their people.