  Recurrent or ephemeral water shortages are a crucial global challenge, in
particular because of their impacts on food production. The global character of
this challenge is reflected in the trade among nations of virtual water, i.e.
the amount of water used to produce a given commodity. We build, analyze and
model the network describing the transfer of virtual water between world
nations for staple food products. We find that all the key features of the
network are well described by a model that reproduces both the topological and
weighted properties of the global virtual water trade network, by assuming as
sole controls each country's gross domestic product and yearly rainfall on
agricultural areas. We capture and quantitatively describe the high degree of
globalization of water trade and show that a small group of nations play a key
role in the connectivity of the network and in the global redistribution of
virtual water. Finally, we illustrate examples of prediction of the structure
of the network under future political, economic and climatic scenarios,
suggesting that the crucial importance of the countries that trade large
volumes of water will be strengthened. D
