Virtual water trade analyzed

Virtual water trade analyzed

New "water footprint" tool could help track water transferred through international trade.

INTERNATIONAL trade of food crops led to freshwater savings worth more than $2 billion in 2005 and had a major impact on local water resource stress, according to a study by the Potsdam Institute for Climate Impact Research in Germany.

Recently released in Ecological Economics, the study analyzed the impact of trade on local water scarcity and found that it is not the amount of water used that counts most but the origin of the water.

Trading food involves the trade of virtually embedded water used for production, and the amount of that water depends heavily on the climatic conditions in the production region. For instance, it takes 2,700 liters of water to produce 1 kg of cereals in Morocco, while the same kilogram of cereals produced in Germany uses only 520 liters.

While parts of India and the Middle East alleviate their water scarcity through importing crops, some countries in Southern Europe export agricultural goods from water-scarce sites, thus increasing local water resource stress.

"Agriculture accounts for 70% of our global freshwater consumption and, therefore, has a huge potential to affect local water scarcity," said lead author Anne Biewald, a postdoctoral researcher in the land use group within the Potsdam institute's climate impacts and vulnerabilities research domain.

The amount of water used in the production of exported agricultural goods is referred to as virtual water trade. So far, however, the study of virtual water has not been able to identify the regional water source but has used national or even global averages instead.

"Our analysis shows that it is not the amount of water that matters but whether global food trade leads to conserving or depleting water reserves in water-scarce regions," Biewald said.

By combining biophysical simulations of the virtual water content of crop production with agro-economic land use and water use simulations, the scientists were able, for the first time, to determine the positive and negative impacts on water scarcity through the international trade of crops, livestock and feed.

The effects were analyzed with high resolution on a subnational level to account for large countries like India or the U.S. with different climatic zones and relating varying local conditions regarding water availability and water productivity. Previously, these countries could be evaluated only through national average water productivity.

"Local water scarcity is reduced through imports of agricultural goods and, therefore, saving regional agricultural production, particularly in parts of India, Morocco, Egypt and Pakistan," Biewald said. However, "scarcity is exacerbated by exports in parts of Turkey, Spain, Portugal, Afghanistan and the U.S."

Despite the fact that Europe alone exports virtual water in food crops worth $3.1 billion, the scientists found that international trade of food crops today globally accounts for water savings worth $2.4 billion.

The study, which focused on data from 2005, found that trade has a considerable impact on agricultural production. Trade reduces global crop production and area due to regional differences in livestock production efficiencies.

For example, the research showed that it takes much less feed input to produce 1 kg of beef in the U.S. than in Africa, so it might be more economical for the world to have regions specializing in certain agricultural products to export to other regions.

"In contrast to popular perception, global food trade and the related virtual water flows indeed offer the possibility of relieving water stress and making global water use more efficient," co-author Hermann Lotze-Campen, co-chair of the Potsdam institute's climate impacts and vulnerabilities research domain, explained. "When it comes to the implementation of policy instruments that affect global trade — such as trade liberalization, import taxes or agricultural subsidies — decision-makers have to take into account the indirect effects on water as well. To connect international food trade to regional water scarcity can contribute to advance this debate."


Water footprint

A new web-based tool developed at the University of Florida has successfully measured the so-called "water footprint" of farms and could provide a better glimpse of water usage in global agricultural production. During trial runs, the new tool was able to measure water consumption at farms in four southern states.

According to a study, the system measures the water footprint of a farm and can help not just growers but also global water managers. Water footprints account for the amount of water used to grow or create almost everything we eat, drink, wear or otherwise use.

"We think this farm-specific, time-specific water footprinting tool is a unique resource that could be used by resource managers and educators to consider water resource sustainability in the context of agricultural production," said Daniel Dourte, a research associate in agricultural and biological engineering at the University of Florida. "We usually think of water management locally and regionally, but when you're accounting for the water footprint of agricultural products, it allows you to see the global nature of that water."

The researchers at the university's Institute of Food & Agricultural Sciences introduced the WaterFootprint tool — which estimates water use in crop production across the U.S. — in the March issue of the journal Agricultural Systems after using it to calculate water consumption at farms in Florida, Georgia, Alabama and Texas.

The WaterFootprint is part of the AgroClimate system developed by Clyde Fraisse, an associate professor of agricultural and biological engineering at the University of Florida. AgroClimate is a web resource aimed primarily at agricultural producers that includes interactive tools and data for reducing agricultural risks.

The WaterFootprint, available at, looks at a farm in a specific year or growing season and measures its water footprint, Dourte said. With the WaterFootprint system, users provide their location by ZIP code, the type of crop, planting and harvesting dates, yield, soil type, tillage and water management.

Dourte said the tool also retrieves historical weather information and uses it to estimate the blue and green water footprints of crop production. (Water footprints categorize water use as "green" for rainfall, "blue" from a freshwater resource and "gray," which is an accounting of water quality after the source has been polluted.)

Water footprints can be viewed at the farm level or globally. For instance, if irrigation water is used to grow crops, it is essentially exported, Dourte explained. Once products are shipped overseas, the water used to grow the commodity goes with it, and it may not return for a long time — if ever. That's a problem if the crop is grown in a region where water is scarce, he said.

"The U.S. is a big agricultural producer. Products are exported, and along with them, water goes to other countries," he said.

For example, when growing soybeans, a producer is indirectly sending the water that was used to grow the crop, and that amounts to about 270 gal./lb. of soybeans, Dourte said.

In addition, coffee beans and shirts made from cotton consume lots of water from the growing period to processing to shipping — with most of that water consumption resulting from evaporation and transpiration during crop growth, he said.

However, there's often a trade-off: Global food trade saves billions of gallons of water each year as food is exported from humid, temperate places to drier locales that would have used much more water to grow crops, Dourte explained.

Understanding the type of water resource being consumed, whether it's from rainfall or irrigation, makes all the difference in assessing water resource sustainability.

Volume:86 Issue:13

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