Science Features

are visible and already occurring trade between nations: today. a global mechanism affecting regional Producing goods and services generally requires water. The water systems water used in the production pro- by A.Y. Hoekstra cess of an agricultural or indus- trial product is called the ‘virtual water’ contained in the product. How can people in Japan affect the hydrological system in About ten years ago, Tony Allan, the United States? And how do people in the from the University of London, introduced this concept. For affect regional water systems in Brazil? The obvious answer is: example, in order to produce 1 through contributing to changes in the global climate system. kg of grain we need 1-2 m3 of We know that local emissions of greenhouse gasses contribute water. Producing 1 kg of cheese to the predicted change of the global climate, thus affecting requires 5 m3 of water and for temperature, evaporation and precipitation patterns elsewhere. 1 kg of beef we need 16 m3 There is however a second mechanism through which coun- of water on average. If one tries affect water systems in other parts of the world. There is country exports a water-intensive a direct link between the demand for water-intensive products product to another country, it (notably crops) in countries such as Japan and the Netherlands exports water in virtual form. and the water used for production of export goods in countries In this way some countries sup- such as the United States and Brazil. The water used for port other countries in their producing export goods for the global market signifi cantly con- water needs. Trade of real water tributes to the change of regional water systems. between water-rich and water-

Japanese consumers put pres- sure on water resources in the Virtual Water Pilot US, contributing to the mining of aquifers, emptying of rivers Project and increased evaporation in The new Global Water System Project (www.gwsp.org) analyses North America. We know the the impacts of human activities on the Global Water System, examples of the mined Ogallala Aquifer and emptied Colorado emphasising the interactions and feedback between the global River. Dutch consumers con- and the regional scale. Virtual water provides a teleconnection tribute, to a highly signifi cant in the Global Water System, linking through global trade water degree, to the water demand in resources in different regions. Virtual water trade also illustrates Brazil. The question put here is: the interactions in the coupled human-environment system, a key how signifi cant are these tele aspect of the Earth System Science Partnership. It has biophysi- connections in the global water cal dimensions, such as climate induced water scarcity as a driver system via the mechanism of or water savings through production in more humid regions, but global trade? Recent research also socio-economic dimensions, such as allocations of water at [1,2] shows that the impact different scales, opportunity costs of water used in export agricul- of global trade on regional ture etc. The GWSP has initiated a Virtual Water Pilot Project, water systems is at least as synthesising information on current virtual water fl uxes and out- important as the impact of cli- lining relevant research questions as a fast track activity. It may mate change on regional water address questions of environmental or socio-economic impacts systems. Although a large part of virtual water trade, or the usefulness of virtual water trade as of the impacts of climate change a tool in an integrated water resources management context, or are yet to come, the impacts of the potential for compensation mechanisms for the global trade on water systems that countries leave in other regions.

2 poor regions is generally impos- drinking water required during agriculture (water use for irri- sible due to the large distances the lifetime of the animal and gation) in the same period was and associated costs, but trade in if relevant other water require- about 2500 Gm3/yr. Taking into water-intensive products (virtual ments such as for cleaning account the use of rainwater by water trade) is realistic. stalls. crops as well, the total water In order to assess the virtual Table 1 gives the estimated use by crops in the world has water fl ows between nations, the virtual water content for a been estimated at 5400 Gm3/yr. basic approach has been to mul- number of products. The given The total water use in the world tiply international trade volumes fi gures represent global aver- for domestic and industrial pur- (ton/yr) by their associated vir- ages. There are very signifi cant poses has been estimated at 1200 tual water content (m3/ton). differences between countries, Gm3/yr. This means that about Trade data have been taken mainly relating to differences in 15% of the water used in the from the United Nations Statis- climate conditions, but in the world for human purposes is not tics Division in New York. The case of livestock products also used for domestic consumption virtual water content of crops relating to differences in animal but for export (in virtual form). has been estimated per crop and diets in different countries. The world’s nations do not per country on the basis of var- The global virtual water have comparable shares in global ious FAO databases (CropWat, trade is estimated to be 1+1012 virtual water trade. Dominant ClimWat, FAOSTAT). The virtual m3/yr in the period 1995-1999, virtual water exporters are the water content of livestock prod- of which 67% relates to inter- USA, Canada, Australia, Argen- ucts has been calculated along national trade of crops, 23% tina and Thailand. Countries with to trade of livestock and live- a large net import of virtual water stock products and 10% to trade are Japan, Sri Lanka, Italy, South of industrial products [1,3,4]. Korea and the Netherlands. Other global studies of global Based on the estimated global virtual water trade show esti- virtual water trade fl ows, we can mates in the same order of mag- draft national virtual water trade nitude [5,6]. For comparison: balances. The balance is calcu- the global water withdrawal for lated by adding all virtual water

Table 1. Virtual water content of a few selected products in m3/ton. Source: [3,4]. the lines of ‘production trees’ that show different product levels [3]. The virtual water con- tent of meat for instance depends Figure 1. National virtual water trade balances over the period 1995-1999. on the virtual water content of Red represents net import, green net export. the animal carcass, which in turn depends on the virtual water content of the live animal. If the carcass of the live animal pro- vides skin for leather as well, the virtual water content of the live animal is divided over car- cass and skin according to the economic value ratio. The virtual water content of a live animal largely depends on the virtual water content of the feed con- Figure 2. Virtual water trade balances of thirteen world regions over the sumed during the lifetime of the period 1995-1999. The arrows show the largest net virtual water fl ows – the most important tele-connections – between regions animal. Added to that is the (virtual water fl ows>100 Gm3).

3 water footprint of 15% of the world water use a nation partly is not for meeting domestic weighs upon demands, but for meeting for- their own domes- eign demands, often located on tic water other continents. In other words, resources and roughly speaking, 15% of the partly on foreign disturbances of regional water water resources systems that have been widely (i.e. the water reported are linked to demands resources of the for water-intensive products in countries from other parts of the world. Given which water- the ongoing process of global- intensive prod- isation, these tele connections ucts are are likely to become increasingly imported). important. Import of virtual Arjen Hoekstra water can thus be UNESCO-IHE Institute for seen as an alter- Water Education, Delft, native source of The Netherlands water, relieving E-mail: [email protected] Figure 3. The real and the virtual water balance of pressure on the China in 1999 (data in Gm3/yr). resources of importing coun- References imports and subtracting all vir- tries. 1. Hoekstra AY and Hung PQ. tual water exports. The national As an example of how the (2002) Virtual water trade: A quantifi cation of virtual water virtual water trade balances real water balance and the vir- fl ows between nations in rela- over the period 1995-1999 are tual water balance of a country tion to international crop trade. Value of Water Research Report shown in Figure 1. Countries link to each other, Figure 3 Series No.11, IHE, Delft, the Netherlands. Downloadable from with net virtual water export shows both balances for China http://www.ihe.nl/vmp/articles/Projects/ (a negative balance) are shown in the year 1999. The total use PRO-Virtual_Water_Trade.html in green colour and countries of domestic water resources in 2. Hoekstra AY. (ed) (2003) Virtual with net virtual water import (a China is 1375 billion m3/yr (59% water trade: Proceedings of the International Expert Meeting on Vir- positive balance) in red colour. ‘green’ water, 41% ‘blue’ water), tual Water Trade, Delft, The Neth- erlands, 12-13 December 2002. Figure 2 shows the virtual water of which 1.2% is used for export. Value of Water Research Report trade balances for thirteen world The water footprint in China Series No.12, IHE, Delft, the 3 Netherlands. Downloadable from regions and also shows the larg- is 1392 billion m /yr, pressing http://www.ihe.nl/vmp/articles/Projects/ est virtual water trade fl ows on domestic resources for 97.6% PRO-Virtual_Water_Trade.html between these regions. and on foreign water resources 3. Chapagain AK and Hoekstra AY. (2003) Virtual water trade: A The virtual water concept for the remaining 2.4%. This is quantifi cation of virtual water offers the possibility to analyse not so much, but is likely to fl ows between nations in relation to international trade of livestock the impacts of consumption pat- increase in the future. China is and livestock products. In: [2].

terns on water use. Per country, just one example in the whole 4. Hoekstra AY and Hung PQ. (2003) we have calculated the cumula- spectrum of cases. Some coun- Virtual water trade: A quanti- fi cation of virtual water fl ows tive virtual water content of all tries, such as the United States, between nations in relation to goods and services consumed by Canada, Australia, Argentina international crop trade. In: [2]. the individuals of the country and Thailand, have net export 5. Zimmer D and Renault D. (2003) Virtual water in food production [1]. In this way we have calcu- of virtual water, so they do and global trade: Review of lated what we call the ‘water not depend on foreign water methodological issues and pre- liminary results. In: [2]. footprint’ of a nation, a term resources. However, an extreme 6. Oki T, Sato M, Kawamura A, chosen in analogy of the ecologi- example at the other end of Miyake M, Kanae S, and Musiake cal footprint [7]. The water foot- the spectrum is Jordan, which K. (2003) Virtual water trade to Japan and in the world. In: [2]. print of a nation is equal to the depending on the year consid- 7. Wackernagel M, and Rees W. use of domestic water resources, ered, relies on foreign water (1996) Our ecological footprint: minus the virtual water export resources to satisfy 60 to 90% of Reducing human impact on the earth. New Society Publishers, fl ows, plus the virtual water its domestic water need. Gabriola Island, B.C., Canada. import fl ows. Generally, the The overall picture is that

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