Optimal Allocation Of Agricultural Water Resources Based On Virtual Water Strategy In Shiyang River Basin

As scare basic resources, water resources occupy a pivotal position in regional social andeconomic sustainable development. How to rationally allocate the region's limited waterresources has become the focus of attention. The traditional way to solve the water shortage isalways to divert water through engineering measures or to save water through technical means,while the virtual water concept provides people with a new way to solve the water shortageproblem through economics means. Virtual water refers to the quantities of water needed toproduce goods and services. The strategy of virtual water refers to an effective means thatwater-scarce countries or regions purchase water-intensive products from the water-richcountry or region by means of trade, to solve the water shortage problem. The virtual water ofagricultural products contains blue and green virtual water, part of the water resources thatsaved by water-scarce countries or regions through the virtual water strategy exist in the formof green water, but these green water can not be artificially configured and only its utilizationcan be increased. Only the blue water can be configured and can be directly used by sectorswith high efficiency of water use, such as industry. So evaluating the blue and green watercontent in the virtual water of agricultural products is an important prerequisite to rationallyuse the virtual water strategy. In Shiyang River Basin of Gansu Province, the water resourcesare shortage, the ecological environment is fragile, the water resources allocation isunreasonable and agricultural water consumption is excessive. The limited water resourceswill be rationally allocated through the theory of virtual water and the concept of blue andgreen water, in order to improve the utilization of green water, achieve the efficient allocationof water resources. The main research contents and the main conclusions obtained of thispaper are as follows:(1) The way to calculate virtual water, blue and green virtual water content ofagricultural products is established based on crop water requirement calculated by themodified Penman formula, effective rainfall for crop growing period, crop unit area yield. Thevirtual water content of agricultural products refers to the water needed by the unit mass of agricultural products, virtual green water content is rainfall used by the unit mass ofagricultural products, and the virtual blue water content is the difference between the two. Thesubdivision of agricultural virtual water provides the basis of calculations in order to furtheroptimize the allocation of agricultural water resources.(2) The virtual water, blue virtual water and green virtual content of main agriculturalproducts, so as wheat, corn, other grains (mainly barley, beans, potatoes, etc), cotton, oilseeds,vegetables, fruits, in Lianzhou, Minqin, Gulang, Tianzhu, Jinchuan, Yongchang of ShiyangRiver Basin are got. And the differences in virtual water content and composition because oftime, space and crop types are analyzed; the virtual water content and composition vary withthe time, space, different types of crops. Take wheat as an example, the order of the virtualwater content of wheat in different districts from small to large is: Yongchang, Liangzhou,Minqin, Jinchuan, Tianzhu, Gulang; and the order of the blue virtual water content of wheat indifferent districts from small to large is: Tianzhu, Yongchang, Liangzhou, Minqin, Jinchuan,Gulang; while the ratio of green virtual water of wheat in Tianzhu is the largest(50.2%), thesmallest ones are in Minqin and Jinchuan(4.0%).(3) Under the premise of priority to the water demand of life, ecology, secondary andtertiary industries, considering the virtual water trade between different districts in ShiyangRiver Basin, and outside the basin, taking the largest benefits of agriculture, the smallestdifferences in per capita use of water resources, the largest utilization ratio of green water astargets, the multi-objective optimal allocation model of agricultural water resources inShiyang River Basin is established, and reasonable allocation of water resources and plantingstructure are obtained.The results show that: in current2007, the proportion of food crops and cash crops is69to31, the net benefit of the unit blue water is3.44yuan per cubic meter, the ratio of cropgreen water use is16.6%. Optimized, the proportions of food crops and cash crops that are50to50,47to53and47to53in2007,2015and2025decreased; The net benefit of the unitblue water that are6.54yuan per cubic meter,7.00yuan per cubic meter,7.35yuan per cubicmeter in2007,2015and2025increased compared with the one before optimization; In2007,per capita water use differences reduce, while those in2015and2025increase a little becauseindustrial water consumption in Jinchuan where the industry developed is higher than that ofother districts; The ratios of crop green water use that are17.9%,21.3%,23.0%increase more,which show that the rainfall utilization of crops increases. Through the virtual water trade ofagricultural products between the districts of Shiyang River Basin, the basin food needs in2007met, while in2015,2025Shiyang River Basin, in addition to internal agricultural virtualwater trade, need additional92062t,193631t food transferred from outside the basin to meet demand. Thus, the administrative region of the crops plays a comparative advantage throughthe implementation of virtual water strategy and the water use efficiency is improved.