Comparative advantage for the areas irrigated with underground blue water in North China Plain.

North China Plain is one of the most important grain-producing areas in China. Because of unevenly distributed precipitation in this semi-arid area, crop production largely relies on underground blue water (UBW) to irrigate, overexploitation of which causes a lot of environmental problems. In this paper, we first defined the representative division of winter wheat irrigation water production efficiency with a support vector machine and genetic algorithm coupling algorithm, then established a model for evaluating the comparative advantage of UBW production efficiency by combining the effective precipitation with the UBW depth, calculated its value in each city, and further proposed the reasonable irrigation water requirement and its distribution under different grain reserves at the targeting year. The result showed that when the typical precipitation (P) is 25% in a targeting year, there is no need to irrigate with UBW; when P=50%, supplying 5% of total winter wheat production (TWP) could save 15% of UBW; when P=75%, supplying 5% of TWP could save 11% of UBW; and when P=75%, supplying 10% of TWP could save up to 28% of UBW. [ABSTRACT FROM AUTHOR]