Theory,Method and Progress on Virtual Water Research

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