Drivers of the virtual water trade

Through the international trade of food commodities, countries virtually export or import the water used for food production, known as virtual water. The international trade network thus implies a network of virtual water flows from exporting to importing countries. The purpose of this study is to identify some controlling factors of the virtual water network by means of multivariate regression analyses, or gravity laws, as often named in economics. Starting from the FAOSTAT database, we reconstruct 25 years (1986-2010) of international virtual water trade values; we then analyze the dependence of the exchanged fluxes on: population, gross domestic product, arable land, virtual water embedded in agricultural production and dietary demand, and geographical distance between countries. Significant drivers are identified for each country considering separately export and import fluxes; temporal trends are outlined and the relative importance of drivers is assessed by a commonality analysis. Results indicate that population, gross domestic product and geographical distance are the major drivers of virtual water fluxes, with a minor (nonnegligible) contribution given by the agricultural production of exporting countries. Such drivers have become relevant for an increasing number of countries throughout the years, with an increasing variance explained by the distance between countries and a decreasing role of the gross domestic product. The worldwide adjusted coefficient of determination of fitted gravity-law model is 0.57 (in 2010), and it has increased in time, confirming the good descriptive capability of selected drivers for the virtual water trade.