Internal and external green-blue agricultural water footprints of nations, and related water and land savings through trade

Abstract

The need to increase food production for a growing world population makes an assessment of global agricultural water productivities and virtual water flows important. Using the hydrology and agro-biosphere model LPJmL, we quantify at 0.5° resolution the blue (irrigation water) and green (precipitation water) virtual water content, i.e. the inverse of water productivity, for 11 of the world's major crop types. Based on these, we also quantify the water footprints (WFP) of all countries, for the period 1998-2002, distinguishing internal and external WFP (virtual water imported from other countries) and their blue and green components, respectively. Moreover, we calculate water savings and losses, and for the first time also land savings and losses, through international trade with these products. The consistent separation of blue and green water flows and footprints, which is needed due to the different sources and opportunity costs of these two water pools, shows that green water globally dominates both the internal and external WFP (84% of the global WFP and 94% of the external WFP rely on green water). Accordingly, some of the major exporters of the crops considered here (e.g. Argentina, Canada) export mainly green virtual water, but traditional rice exporters such as India and Pakistan mainly export blue virtual water. The external WFPs are found to be relatively small (6% of the total global blue WFP, 16% of the total global green WFP). Nevertheless, current trade saves significant water volumes and land areas (~263 km3 and ~41 Mha, respectively, equivalent to 5% of the sowing area of the crops considered here and 3.5% of the annual precipitation on this area). Linking the proportions of external to internal blue/green WFP with the per capita WFPs allows recognizing that only a few countries consume more water from abroad than from their own territory and have at the same time above average WFPs. Thus, countries with high levels of per capita water consumption affect mainly the water situation in their own country.