Background
Despite the progress made in water use assessments, previous studies either lack spatial details and resolutions, or merely emphasize on blue water uses, or focus on water withdrawal while ignore consumptive water uses. We estimate consumptive water use and proportion of green water in the production of 17 major crops with a spatial resolution of 30 arc-minutes on the land surface.Data
The crop distribution maps are obtained from the Center for Sustainability and the Global Environment (SAGE) at the University of Wisconsin-Madison. The data on the harvested area of the irrigated crops are taken from the Institute of Physical Geography of the University of Frankfurt (Main), Germany. The amount of fertilizer applied per country and crop is derived from the statistical report by the International Fertilizer Industry Association.Methods
Crop yield, crop evapotranspiration and crop water productivity of 17 major crops are simulated with a spatial resolution of 30 arc-minutes with a GIS-based EPIC model (GEPIC).Results
The results show that the global annual consumptive water use (CWU) of the crops considered was about 3823 km3 yr-1 for the period 1998-2002. Over 80% of this amount was from green water. Globally, around 94% of the virtual water trade among countries had its origin in green water. This is partly related to the low opportunity cost of green water as opposed to blue water. High levels of net virtual water import generally occur in countries with low CWU on a per capita basis, where a virtual water strategy can be an option of water management to compensate for domestic lack of water resources for food production.Status
A paper has been published in Water Resources Research.Citation
Liu, J., A. J. B. Zehnder, and H. Yang, 2009. Global consumptive water use for crop production: The importance of green water and virtual water, Water Resources Research, 45, W05428, doi:10.1029/2007WR006051.
Figure: Spatial distribution of consumptive water use (CWU) for crop production per grid cell of 30 arc-minutes (average over 1998-2002)