The global component of freshwater demand and supply

In the world of today, people in Japan indirectly affect the hydrological system in the United States and people in the Netherlands indirectly impact on the regional water systems in Brazil. Much has been reported about the expected effects of past and ongoing local emissions of greenhouse gasses on the future global temperature, evaporation and precipitation patterns. Little attention has been paid however to a second mechanism through which people affect water systems in other parts of the world. This second mechanism, which is actually much more visible already today, is through global trade. International trade in agricultural and industrial commodities creates a direct link between the demand for water-intensive commodities (notably crops) in countries such as Japan and the Netherlands and the water use for production of export commodities in countries such as the United States and Brazil. The water use for producing export commodities to the global market significantly contributes to the change of regional water systems. Japanese consumers put pressure on water resources in the US, contributing to the mining of aquifers and emptying of rivers in North America. We know the examples of the mined Ogallala Aquifer and emptied Colorado River. Dutch consumers contribute to a significant degree to the water demand in Brazil.