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Virtual water trade (also known as trade in embedded or embodied water) refers to the hidden flow of water if food or other commodities are traded from one place to another. For instance, it takes 1,600 cubic meters of water on average to produce one metric tonne of wheat. The precise volume can be more or less depending on climatic conditions and agricultural practice. Hoekstra and Chapagain have defined the virtual-water content of a product (a commodity, good or service) as "the volume of freshwater used to produce the product, measured at the place where the product was actually produced". It refers to the sum of the water use in the various steps of the production chain. Professor John Anthony Allan from King's College London and the School of Oriental and African Studies introduced the virtual water concept,〔("Looming water crisis simply a management problem" ) by Jonathan Chenoweth, New Scientist 28 Aug., 2008, pp. 28-32. 〕 to support his argument that countries in the Middle East can save their scarce water resources by relying more on import of food. For his contributions he was awarded the 2008 Stockholm Water Prize.〔http://www.siwi.org/sa/node.asp?node=25〕 Allan stated: "The water is said to be virtual because once the wheat is grown, the real water used to grow it is no longer actually contained in the wheat. The concept of virtual water helps us realize how much water is needed to produce different goods and services. In semi-arid and arid areas, knowing the virtual water value of a good or service can be useful towards determining how best to use the scarce water available." There are, however, significant deficiencies with the concept of virtual water that mean there is a significant risk in relying on these measures to guide policy conclusions. Accordingly, Australia's National Water Commission considers that the measurement of virtual water has little practical value in decision making regarding the best allocation of scarce water resources.〔http://www.nwc.gov.au/__data/assets/pdf_file/0005/11885/DistilledJuly2008.pdf〕 ==Virtual water trade== Virtual water trade refers to the idea that when goods and services are exchanged, so is virtual water. When a country imports one tonne of wheat instead of producing it domestically, it is saving about 1,300 cubic meters of real indigenous water. If this country is water-scarce, the water that is 'saved' can be used towards other ends. If the exporting country is water-scarce, however, it has exported 1,300 cubic meters of virtual water since the real water used to grow the wheat will no longer be available for other purposes. This has obvious strategic implications for countries that are water-constrained such as those found in the Southern African Development Community (SADC) area 〔Turton, A.R. 1998. The Hydropolitics of Southern Africa: The Case of the Zambezi River Basin as an Area of Potential Co-operation Based on Allan’s Concept of ‘Virtual Water’. Unpublished M.A. Dissertation, Department of International Politics, University of South Africa, Pretoria, South Africa.〕〔Turton, A.R., Moodley, S., Goldblatt, M. & Meissner, R. 2000. An Analysis of the Role of Virtual Water in Southern Africa in Meeting Water Scarcity: An Applied Research and Capacity Building Project. Johannesburg: Group for Environmental Monitoring (GEM).〕〔Earle, A. & Turton, A.R. 2003. The Virtual Water Trade amongst Countries of the SADC. In Hoekstra, A. (Ed.) Virtual Water Trade: Proceedings of the International Experts Meeting on Virtual Water Trade. Delft, the Netherlands, 12–13 December 2002. Research Report Series No. 12. Delft: IHE. Pp. 183-200.〕 Water-scarce countries like Israel discourage the export of oranges (relatively heavy water guzzlers) precisely to prevent large quantities of water being exported to different parts of the world. In recent years, the concept of virtual water trade has gained weight both in the scientific as well as in the political debate. The notion of the concept is ambiguous. It changes between an analytical, descriptive concept and a political induced strategy. As an analytical concept, virtual water trade represents an instrument which allows the identification and assessment of policy options not only in the scientific but also in the political discourse. As a politically induced strategy the question is, whether virtual water trade can be implemented in a sustainable way, whether the implementation can be managed in a social, economical and ecological fashion, and for which countries the concept offers a meaningful option. The data that underlie the concept of virtual water can readily be used to construct water satellite accounts, and brought into economic models of international trade such as the GTAP Computable General Equilibrium Model. Such a model can be used to study the economic implications of changes in water supply or water policy, as well as the water resource implications of economic development and trade liberalisation. In sum, virtual water trade allows a new, amplified perspective on water problems: In the framework of recent developments from a supply-oriented to a demand-oriented management of water resources it opens up new fields of governance and facilitates a differentiation and balancing of different perspectives, basic conditions and interests. Analytically the concept enables one to distinguish between global, regional and local levels and their linkages. This means, that water resource problems have to be solved in ''problemsheds''〔Earle, A. 2003. Watersheds and Problemsheds: A Strategic Perspective on the Water/Food/Trade Nexus in Southern Africa. In Turton, A.R., Ashton, P.J. & Cloete, T.E. (Eds.) Transboundary Rivers, Sovereignty and Development: Hydropolitical Drivers in the Okavango River Basin. Pretoria & Geneva: AWIRU & Green Cross International. Pp. 229-249.〕 if they cannot be successfully addressed in the local or regional watershed. Virtual water trade can thus overcome the hydro-centricity of a narrow watershed view. According to the proceedings of a 2006 conference in Frankfurt, Germany, it seems reasonable to link the new concept with the approach of Integrated Water Resources Management. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「virtual water」の詳細全文を読む スポンサード リンク
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