Water Requirement with Irrigation Expansion in Jingtai Irrigation District, Northwest China: The Need to Consider Irrigation-Induced Local Changes in Evapotranspiration Demand

Abstract

Because water diverted from the Yellow River has been used for irrigation in 1972, obvious changes in evapotranspiration demand (denoted by reference evapotranspiration) have been observed in the Jingtai Irrigation District, Northwest China. Increasing irrigation-water consumption corresponding to irrigation expansion led to less local evapotranspiration demand after 1972. The crop and irrigation-water requirements per unit area were influenced by the changes in evapotranspiration demand. A simple prediction approach based on the complementary relationship of evapotranspiration was used to estimate the irrigation-induced changes in evapotranspiration demand and their influences on irrigation-water requirement. Future variations in net irrigation requirement per unit area under different irrigation scenarios at 50% and 75% precipitation levels were evaluated. Irrigation requirements per unit area would decrease under irrigation-expansion scenarios but increase under irrigation-reduction scenarios corresponding to the irrigation-induced changes in evapotranspiration demand. Irrigation-induced local changes in evapotranspiration demand should be seriously considered for irrigation planning and management.