Food production requires adequate soils, climate, and water. Roughly 70 percent of the freshwater appropriated by humans worldwide is used for food production. In the absence of trade, people rely on local freshwater resources to grow food. However, when water limitations constrain food production to the point that there is not enough food for everyone, the trade of food commodities provides a mechanism by which regions can compensate for inadequate local water resources.

Food production requires adequate soils, climate, and water. Roughly 70 percent of the freshwater appropriated by humans worldwide is used for food production. In the absence of trade, people rely on local freshwater resources to grow food. However, when water limitations constrain food production to the point that there is not enough food for everyone, the trade of food commodities provides a mechanism by which regions can compensate for inadequate local water resources.

The United States’ National Intelligence Council and the European Union’s Institute for Security Studies estimate that more than one billion people currently live in regions where the demand for water exceeds the local supply. These populations are sustained only via importation of the “virtual water” resources associated with foreign food production.

Global food security depends, in part, on the virtual water trade. The transfer of virtual water from food-producing regions to food-importing regions provides a way to maximize the use of global water resources; allows overpopulated and water-poor countries to meet their food demand; and can ameliorate the effects of drought on local food production. In some schools of thought, the virtual-water trade acts to reduce societal water stress, malnourishment, and water wars.

However, this “globalization of water” has adverse impacts as well. It decouples a population from the production of its food and allows the population to grow at a rate that is unsustainable with respect to local water resources. The decoupling of resources and population can also cause people to care less about the environment they live in. And although the virtual water trade mitigates local water stresses, it also lowers societal resilience to drought by reducing the water options available during a food crisis. Moreover, differences in access to water and trade introduce the potential for large inequalities to arise among nations.

Tracking the flow of virtual water. Detailed population data and trade information for 309 plant and animal food commodities, combined with production estimates of virtual water by crop commodity and country, have made it possible to reconstruct the network of virtual water flows from 1986 through 2008. This network is comprised of links (imports and exports) representing virtual water transfers between countries. The network has changed significantly over the past few decades. The total number of trade connections has increased from 8,213 to 15,789, with the number of active trading nodes (countries) increasing from 205 to 232. Moreover, the total trade in virtual water has increased from roughly 1 trillion cubic meters to about 2.2 trillion cubic meters. This increase has occurred at a rate that exceeded that of population growth, resulting in an overall increase in trade of 150 cubic meters per person per year between 1986 and 2008.

The network of virtual water trade is highly dynamic, with very few permanent links; its structure depends on many factors, including socio-economic and political conditions, demographic dynamics, and water availability. Some of the changes in this network are due to political transformations, such as the dissolution of the former Soviet Union. While both the total virtual water flow and number of trade connections have increased, virtual water trade remains unevenly distributed. In fact, 50 percent of the virtual water flows through only 1.1 percent of the links, and approximately 40 percent of the net virtual water exports come from Brazil, Argentina, and the United States — countries that account for only 5.7 percent of the global population. Worldwide, 90 percent of virtual water exports are controlled by only 32 percent of the population. The largest net importers of virtual water in 2008 were China and Japan. African nations have low connectivity to the global network, with relatively small amounts of virtual water moving to and from African countries.

Depending on “foreign” freshwater. In 1986, 40 percent of the world’s population lived in countries that were net importers of virtual water. By 2008, 60 percent of the global population was living in countries that were net importers. This increased reliance on “foreign” freshwater, combined with the unequal distribution of water resources, has significant implications. If the observed trend continues, an increasing majority of the global population will depend on virtual water imports from fewer and fewer countries. At some point, the virtual water available through international trade will become insufficient to sustain the populations in water-stressed regions.

While technological advances may enhance the efficiency of water usage in food production, climate change impacts on precipitation patterns are expected to modify the global agricultural landscape. Major agricultural regions in the United States, Brazil, and Argentina — currently major exporters of virtual water — are likely to undergo decreases in precipitation, thereby further enhancing the uncertainty of the virtual water trade and global food security. It is thus critically important to gain an understanding of the factors and countries that contribute to changes in the redistribution of virtual water resources, in order to assess how the global community might respond to environmental stresses resulting from climate change.