Method for Calculating Virtual Water Trade and Demonstration

The concept of and trade supply us a strategic instrument to achieve security.Firsty,this paper analyses the disadvantage of traditional method.Secondy,we propose the extended input-output model to account for flows.We extend the input-output table by adding 1 row in physical units to measure the amounts of virtual fresh water and by 1 column to represent virtual waster water discharged by economic production processes.This method can calculates the flows directly and exactly.It not only calculates the fresh flows but also discuss the consequence on environment variable of waste water.Finally,we assess the virtual fresh water flows and virtual waste water in north China and give some suggestions on regional trade strategy in China.