Modeling past and future structure of the global virtual water trade network

Climate change and socio-economic development place an increasing pressure on essential natural resources, such as arable land and freshwater. The international food trade can save water globally by redistributing commodities produced relatively more water-efficiently. We focus on the global virtual water trade network associated with international food trade from 1986-2008. This study aims to determine which variables control the network's structure and temporal evolution, and to estimate changes in the network under future scenarios. Our fitness model reproduces both the topological and weighted characteristics of the network for the whole period. Undirected and directed network properties are well reproduced in each year, assuming as sole controls simple national-level variables. The future structure of the network is estimated using climate and socio-economic projections, showing that volumes of virtual water traded will become increasingly heterogeneous and the importance of dominant importing nations will further strengthen. Exceedance probability distribution of the undirected node degree (k, panel a) and strength (s, panel b): comparison of data and model results in 1986, 1992, 2000 and 2008, respectively. The similarity between data and model is confirmed in each year by a Kolgmogorov - Smirnov statistical test, the results of this test are shown in the "KS test'' box.