Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 10 3 2006 10.5194/hess-10-443-2006 http://www.hydrol-earth-syst-sci.net/10/443/2006/ http://www.hydrol-earth-syst-sci.net/10/443/2006/hess-10-443-2006.html http://www.hydrol-earth-syst-sci.net/10/443/2006/hess-10-443-2006.pdf 443 454 2006-06-30 Virtual water trade: an assessment of water use efficiency in the international food trade H. Yang hong.yang@eawag.ch L. Wang K. C. Abbaspour A. J. B. Zehnder Swiss Federal Institute for Environmental Science and Technology, Ueberlandstrasse 133, 8600 Duebendorf, Switzerland Board of Swiss Federal Institute of Technology, ETH Zentrum, 8092 Zurich, Switzerland Amid an increasing water scarcity in many parts of the world, virtual water trade as both a policy instrument and practical means to balance the local, national and global water budget has received much attention in recent years. Building upon the knowledge of virtual water accounting in the literature, this study assesses the efficiency of water use embodied in the international food trade from the perspectives of exporting and importing countries and at the global and country levels. The investigation reveals that the virtual water flows primarily from countries of high crop water productivity to countries of low crop water productivity, generating a global saving in water use. Meanwhile, the total virtual water trade is dominated by green virtual water, which constitutes a low opportunity cost of water use as opposed to blue virtual water. A sensitivity analysis, however, suggests high uncertainties in the virtual water accounting and the estimation of the scale of water saving. The study also raises awareness of the limited effect of water scarcity on the global virtual water trade and the negative implications of the global water saving for the water use efficiency and food security in importing countries and the environment in exporting countries. The analysis shows the complexity in evaluating the efficiency gains in the international virtual water trade. The findings of the study, nevertheless, call for a greater emphasis on rainfed agriculture to improve the global food security and environmental sustainability. Allan, J. A.: Fortunately there are substitutes for water otherwise our hydro-political futures would be impossible, ODA, Priorities for water resources allocation and management, ODA, London, 13–26, 1993. Cosgrove W. J. and Rijsberman F. R.: Making Water Every body's Business, Earthscan Publications Ltd, London, 2000. Chapagain, A. K. and Hoekstra, A. Y.: Virtual water trade: A quantification of virtual water flows between nations in relation to international trade of livestock and livestock products, Virtual water trade, in: Proceedings of the international expert meeting on virtual water trade, Delft, The Netherlands, edited by: Hoekstra A. Y., Res. Rep. Ser. No. 12, 2003. Davis, J. R. and Koop, K.: Eutrophication in Australian rivers, reservoirs and estuaries – a southern hemisphere perspective on the science and its implications, Hydrobiologica, 559, 23–76, 2006. Falkenmark, M. and Widstrand, C.: Population and water resources: a delicate balance, Population Bull., 47, 3, 1992. Falkenmark, M.: Land-water linkages – A synopsis, Land and Water Integration and river Basin Management, FAO Land and Water Bulletin, No. 1, 15–16, FAO, Rome, Italy, 1995. FAO: Crop Water Requirements, Irrigation and Drainage Papers No. 24, FAO, Rome, 1986. FAO: FAOSTAT, the Database of the Food and Agricultural Organization of the UN, 2004a. FAO: AQUASTAT, the Database of Land and Water Division of FAO, 2004b, http://www.fao.org/ag/agl/aglw/aquastat/main/index.stm. Fraiture, C., Cai, X., Amarasinghe, U., Rosegrant, M., and Molden, D.: Does International Cereal Trade Save Water? The Impact of Virtual Water Trade on Global Water Use, Comprehensive Assessment Research Report 4, International Water Manage. Institute, Colombo, 2004. Gleick, P.: Soft path's solution to 21st-century water needs, Science, 320, 1524–1528, 2003. Hoekstra, A. Y. and Hung, P. Q.: Virtual water trade: a quantification of virtual water flows between nations in relation to international crop trade, in: Virtual water trade, in: Proceedings of the international expert meeting on virtual water trade, Delft, The Netherlands, edited by: Hoekstra A. Y., Res. Rep. Ser. No. 12, 2003. Hoekstra, A. Y. and Hung, P. Q.: Globalization of water resources: International virtual water flows between nations in relation to international crop trade, Global Environmental Change, 15, 45–56, 2005. Merrett, S.: Virtual water – A discussion – Virtual water and Occam's razor, Water International, 28, 103–105, 2003. Molden, D., Sakthivadivel, R., Perry, C.J., de Fraiture, C., and Kloezen, W. H.: Indicators for comparing performance of irrigated agricultural systems, Research Report 20, International Water Management Institute, Colombo, Sri Lanka, 1998. Molden, D. and Bos, M. G.: Improving basin water use in linked agricultural, ecological and urban systems: seeking new flow paths and avoiding dead ends, Water Sci. Technol., 51, 147–154, 2005. Oki, T. and Kanae, S.: Virtual water trade and world water resources, Water Sci. Technol., 49, 203–209, 2004. Postel, S.: Dividing the Waters: Food Security, Ecosystem Health, and the New Politics of Scarcity, World Watch Institute, Washington, DC, USA, 1996. Postel, S.: Pillar of Sand: Can the Irrigation Miracle Last?, Norton, New York, 1999. Qadir, M., Boers, T. M., Schubert, S., Ghafoor, A., and Murtaza, G.: Agricultural water management in water-starved countries: challenges and opportunities, Agric. Water Manage., 62, 165–185, 2003. Rijsberman, F.: Troubled water, water troubles: overcoming an important constraint to food security, In: Sustainable food security for all by 2020, Proceedings of an International Conference, 4–6 Sept., Bonn, Germany, 2002, http://www.ifpri.org/pubs/books/2020conpro.htm. Rockström, J., Gordon, L., Falkenmark, M., Folke, C., and Engvall, M.: Linkages among water vapor flows, food production and terrestraial ecosystems services, Concervation Ecology, 3, 1–28, 1999, www.consecol.org/vol3/iss2/art5. Rosegrant, M., Cai, X., and Cline, S.: World water and food to 2025, International Food Policy Research Institute (IFPRI), Washington D. C., 2002. Seckler, D., Amarasinghe, U., Molden, D., Rhadika, de S., and Barker, R.: World water demand and supply, 1990 to 2025: Scenarios and issue, Res, Rep. No. 19, 1998. Savenije, H.: Water scarcity indicators: the deception of the numbers, Phys. Chem. Earth (B), 25, 199–204, 2000. Shaffer, E. R. and Brenner, J. E.: International trade agreements: hazards to health?, Int. J. Health Services, 34, 467–481, 2004. United Nations Statistic Division (UN): Commodity trade statistics data base (COMTRADE), CD-Rom, 2004. United States Agricultural Department (USDA): Census of Agriculture, 2003, www.nass.usda.gov/census. Wichelns, D.: The role of "virtual water" in efforts to achieve food security and other national goals, with an example from Egypt, Agric. Water Manage., 49, 131–151, 2001. Würtenberger, L., Koellner, T., and Binder, C.: Virtual land use and agricultural trade: estimating environmental and social-economic impacts, Ecol. Econ., 57, 679–697, 2006. Yang, H., Reichert, P., Abbaspour, K. C., and Zehnder, A. J. B.: A water resources threshold and its implications for food security, Environ. Sci. Technol., 37, 3048–3054, 2003. Yang, H. and Zehnder, A. J. B.: Water scarcity and food import – a case study for southern Mediterranean countries, World Development, 30, 1413–1430, 2002a. Yang, H. and Zehnder, A. J. B.: Water endowments and virtual water trade, Gaia, No. 4, 267–270, 2002b. Zehnder, A. J. B., Yang, H., and Schertenleib, R.: Water issues: the need for actions at different levels, Aquatic Sciences, 65, 1–20, 2003. Zimmer, D. and Renault, D.: Virtual water in food production and global trade: review of methodological issues and preliminary results, in: Virtual water trade, Proceedings of the international expert meeting on virtual water trade, Delft, The Netherlands, edited by: Hoekstra A. Y., Res. Rep. Ser. No. 12, 2003.