Food exports can drain arid regions

Dry regions ‘export’ water as agricultural products

About a fifth of the water that humankind now uses gets exported from its original country to another — though rarely as anything that can splash into a glass.

BIG FLOWS Countries shown in green exported more virtual water than they imported from 1995 to 2005. Yellow and red countries were net importers. (Virtual water is water consumed in producing crops or industrial goods.) Hoekstra and Mekonnen/PNAS 2012

Understanding the big blue picture of water resources means getting over the notion that water is wet. Ninety-two percent of water used planetwide goes into growing crops, according to the latest accounting from Arjen Hoekstra and his water research group at the University of Twente in the Netherlands. So for 1996 through 2005, Hoekstra and colleagues tracked “virtual water,” a combination of actual liquid and the shares of water used in industry and in growing wheat, beef and other products.

This accounting highlights the various degrees to which nations depend on foreign water. Some arid countries take a whopping portion of their virtual water from outside their borders (Israel, 82 percent, Kuwait, 90 percent), but so do relatively watery places such as the United Kingdom (75 percent) and the Netherlands (95 percent), the researchers report online February 13 in the Proceedings of the National Academy of Sciences. The United States, which exports more virtual water than it imports, still reaches outside its borders for 20 percent of its consumption.

For the decade studied, China took only 10 percent of its virtual water from abroad. Yet the researchers note that the economically flourishing country as a matter of policy is now leasing and buying land in Africa to secure its food — and virtual water supply.

Export/import balances have their ironies. “There are exporting regions that do have a lot of water stress,” Hoekstra says. Northern China with its arid expanses overall exports virtual water to relatively wet southern China, and India’s dry Punjab is likewise a substantial exporter of virtual water.

A worldwide trend toward eating more animal products and processed foods could increase demands for water. Producing a gram of protein in milk, eggs and chicken meat typically requires at least half again as much water as providing a gram of legume protein, Hoekstra and Twente colleague Mesfin Mekonnen reported online January 24 in Ecosystems. Creating a half-liter bottle of a sugar-sweetened soft drink requires between 170 and 310 liters of water, Hoekstra’s group has calculated. About 95 percent of this water total goes into growing and processing the ingredients, although the amount varies considerably depending on the kind of sweetener and where it’s produced.

The new paper offers little detail about the industrial side of humankind’s water footprint, says ecological economist Klaus Hubacek of the University of Maryland in College Park. Even though agriculture dwarfs its demands, industrial water matters, certainly in terms of pollution. Hubacek and his colleagues are working on their own analysis that will illuminate how the purchase of inedible products affects water.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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