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‘Virtual Water’ - A New Way to Look at Climate Impacts

By Tara Thean

While international trade results in carbon emissions thanks to the fossil fuels burned by planes, trucks and ships, a Princeton University research team has found that world trade could also mean more efficient water use as a side benefit. And since water is a key resource in the production of climate-friendly energy sources, including hydroelectric and nuclear power, that could at least partially offset trade’s negative impact.

Focusing on agriculture, which accounts for 80 percent of freshwater consumption worldwide, the researchers examined trade through the lens of what they call “virtual water” — a measure of how much water goes into the production of a bushel or a kilogram of a given crop. “It’s like the carbon footprint concept, but for water,” Princeton civil and environmental engineering graduate student Carole Dalin, lead author of a paper on the topic in Proceedings of the National Academy of Sciences, said in an interview.

Watering soybeans, Keya Paha County, Nebraska. 
Credit: foto3116/flickr

According to Dalin and her colleagues, it turns out that nations with inadequate water resources also have lower crop yields per acre. In these places, in other words, it takes more water to produce the same amount of corn or soy or barley. Food exported from water-rich areas to water-poor areas, therefore, amounts to a transfer not just of food, but of water efficiency. Overall, Princeton civil and environmental engineering professor Ignacio Rodríguez-Iturbe said, “This lowers the average water footprint of the whole world population.”

In order to carry out their research, the team focused on the trade of 58 food commodities made from barley, corn, rice, soy, and wheat, as well as three livestock products, and used virtual water content simulations to quantify how much water went into producing a unit of a commodity in different countries. The virtual water footprint is a relatively new concept, according to Dalin, but one that is quickly catching on in scientific conversation.

The biggest players in the trade of virtual water have been the U.S. and China, the study noted. The U.S. was the biggest virtual water exporter for most of the 22-year research period, while China replaced Japan as the leading virtual water importer in 2001. Together, the two countries accounted for 35 percent of the world’s virtual water trade volume in 2007. Rodríguez-Iturbe attributes China’s higher virtual water imports to the country’s growing GDP and the resulting spike in meat consumption and thus demand for animal feed such as soy.

When a new domestic trade policy opened the option of soybean meal imports into China in 2000-2001, soy from the U.S., Brazil, and Argentina began flowing into the country. Because these three countries are able to use less water in soy production than China, their soy exports to China contributed to 96 percent of soy-associated water savings in 2007.

In general, Asia has recorded significant growths in virtual water trade volume, with its virtual water imports growing by more than 170 percent. Meanwhile, virtual water trade within the U.S. more than quadrupled from 1986-2007. Overall, the volume of this global virtual water trade is booming. It doubled from 1986 to 2007 – faster than the rate of population growth, according to the study.

Like most things, the virtual water trade boom is not without its drawbacks. If water-poor countries rely on food imports from the water-rich, they may have less incentive to manage their own water resources, according to Rodríguez-Iturbe, and rising demand for Brazil’s soybean products has meant more deforestation of the Amazon rainforests to make way for soybean plantations.

But the international food trade could also be a refuge for countries whose food production is hampered by drought or unfavorable weather patterns — the very changes that are likely to accompany climate change.

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By PalB (New York, NY 10018)
on October 19th, 2012

Thanks for sharing such a useful article.
This is a new angle to the conventional water mapping w.r.t. the usage in agriculture.
Looking forward to more such updates.

Reply to this comment

By Dave (Basking Ridge, NJ 07920)
on October 19th, 2012

The virtual water concept is a powerful tool for water resource accounting and analysis. However, although I appreciate the report, I think it is important to point out that this study did not differentiate climate impacts in quite the way the title given here implies. The virtual water concept allows for real water accounting and provides a perspective on global trade in those terms ”“ as in this very interesting network study. As I understand it, a major conclusion of this study is that this trade network adjusted itself so as to effectively improve the efficiency of global water usage. That is an interesting perspective. It brings to mind complexity theory in so far as complex systems (such as this global network) tend to exhibit levels of self organization.

The scope of this study by its own admission does not extend to qualifying the risks built into the resulting global virtual water network that are associated with the natural dynamics of water resources. This speaks to sustainability directly in that water resources are not fixed. This year’s massive US drought emphasizes that and of course climate change predictions foretell global changes in water supply and growing fresh water shortages. Beyond that though the Brazil soy bean example given in the paper indeed illustrates one type of pitfall or negative feedback ”˜dynamic’ impacting local water resources that is connected with the exploitation of natural local resources via such trade. So I therefore wonder if in years to come it might nevertheless be discovered in hindsight by a similar type of analysis just if, how and how well this global virtual water trade network ”˜self-organized’ to accommodate global sustainability in terms of water.

I found some interesting graphics and information at this site:  For example:

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By Gail Zawacki (Oldwick, NJ)
on October 22nd, 2012

“If water-poor countries rely on food imports from the water-rich, they may have less incentive to manage their own water resources…”

They may also have less incentive to manage their overpopulation problem, and isn’t that at the root of all our other - climate change, resource overextraction and peak oil, and pollution - problems?

How anyone can conceive of the transfer of water as more efficient and therefor a net positive for our finite earth strikes me as terminally afflicted with optimism bias.

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By Dave (Basking Ridge, NJ 07920)
on October 23rd, 2012

Response to Gail:

In one sense I think your concerns about the globalization of water are valid.  I have seen one study suggesting that this reduces net resilience to shortages. This strikes me as self-evident.  Regarding globalization in general, one can argue that economic globalization is a mixed ”˜blessing’ in economic regards too. However to your other point, the virtual water network is a property of global trade, not a cause. People didn’t generally set out to share water via this trade network. Instead it is a parameter or measure of global trade in terms of not only food but also manufactured goods, raw materials and so on.  This report provides data.   If you check it out you will see that it’s a mixed bag. The US apparently gets a lot of its external virtual water from the Yangtze basin in China.  Also, in the US, per capita water consumption is very high compared with the global average, and well over twice that of India and China, but the US population density and rate of growth is comparatively low. Western parts of the US, large areas of Australia and much of the Middle East are very water poor regions.  Would you, for instance, recommend that Californians consider reducing the local population and stop importing virtual water from other parts of the country and overseas?

Let us not forget that climate change is part of the equation.  For instance, climate change is widely considered to be at least partly responsible for the reduction in freshwater supply in the western US. The US is also the world’s second largest emitter of GHG’s. Active efforts to mitigate climate change do not involve population reduction.  Before recommending that perhaps you should first consider which foot the shoe is on.

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