Theory,Method and Progress on Virtual Water Research
虚拟水研究的理论、方法及其主要进展

The term "Virtual Water" was coined by Tony Allan at a seminar at SOAS in 1993 with the background of water commercialization and resources globalization.Virtual water is the water needed to produce agricultural commodities.Since the term was coined,"Virtual water" has become popular in various water research fields due to its vivid expression and extensive meaning.The purpose of this article is to give an introduction of the concept of "Virtual water",quantify methods of virtual water content calculation and review research progress on virtual water.First,the definition of "Virtual water" and relevant concepts such as "Virtual water content","Virtual water export","Virtual water import","Virtual water flow",and "Virtual water balance" are introduced. In addition,"Water footprint" concept which is derived from "Ecological footprint" and "Virtual water" are also discussed,and there are different "Water footprint" concepts including "Nation's water footprint","Individual water footprint","Blue water footprint vs.green water footprint","Total water footprint vs.evaporation water footprint".Secondly,the basic theories of "Virtual Water" are expanded with "Resources Flows","Resources Substitution" and "Comparative Advantage".The quantitative methods for calculating virtual water content of products are introduced.Virtual water content of product has two different values when estimated by production place and consumption place.Virtual water content of crop and crop products can be calculated by making a distinction between primary products,processed products,transformed products,by-products,multiple products and low or non-water consumptive products.For livestock and livestock products,the method of 'production trees' is usually adopted.The paper summarizes the applications of "Virtual Water" and research advances in different fields.Currently,the researches of virtual water mainly focus on three aspects: virtual water and water security,virtual water trade and virtual water flow,and water footprint.The authors consider "Virtual Water" as a new viewpoint of water resource and virtual water will be an innovative field of relevant researches.For example,the concept of "water footprint" can be applied in the study of water resources carrying capacity to solve the problem with which the indexes of water resources carrying capacity were not consistent in the past.Therefore,it is very important to develop the virtual water research in China and the direction of "Virtual Water" research in China has been pointed out.