Research on the virtual water composition and virtual water trade for agriculture in Beijing

Based on the irrigation norm of typical district and county, and revised by the isoline map of Chinese crops water demand, the change of crops program was analyzed as well as the agricultural water use and its GDP benefits. Then the virtual water was calculated for years. At last, the input-output method was used to calculate the trade of virtual water in Beijing. As the results, the virtual water for cereal crops has been decreasing in Beijing, from 1.832 × 109 m3 in 1990 to 4.283 × 108 m3 in 2004. Otherwise the virtual water for technical crops has been increasing, which is from 9.06 × 108 m3 in 1990 to 1.492 × 109 m3 in 2004. On the whole, the virtual water for crops has been decreasing in Beijing. From the angle of primary products Beijing is a virtual water importing area. Virtual water importing of annual average is 2.37 × 108 m3, which is about 5.93% of the total water of Beijing. Virtual water has been an important supplement of local real water of Beijing.