Evaluation on irrigation efficiency of irrigation district in arid region based on evapotranspiration estimated from remote sensing data

Abstract: To evaluate the irrigation efficiency of irrigation districts in arid regions where crop growth relies heavily on irrigation, a new evaluation indicator, coefficient of irrigation water effective utilization, was proposed. The difference of evapotranspiration and precipitation in irrigated land during the crop growing season was considered as the effective use of irrigation water, and the ratio of effective use of irrigation water and net water diversion to the irrigation district was defined as the coefficient of irrigation water effective utilization (ηe). With the development of a remote sensing evapotranspiration technique in recent decades, spatial and temporal variations of evapotranspiration can be estimated with acceptable precision. Then ηe can easily be estimated from evapotranspiration and measured precipitation and net water diversion, which can avoid the difficulties of accurate measurement or simulation of irrigation water stored in the crop root zone in a traditional irrigation water use efficiency evaluation. A case study in the Hetao irrigation district in North China was carried out to estimate the coefficient of irrigation water effective utilization throughout the period 2000-2010 based on remote sensing evapotranspiration data calculated by the SEBAL (Surface Energy Balance Algorithm for Land) model, meteorological data, and water diversion data. Results indicated that ηe tends to increase with the implementation of water-saving irrigation projects. ηe varied from 0.547 to 0.715 during 2000―2010 and ηe decreased with precipitation and net water diversion. The correlation coefficients between ηe and precipitation, and ηe and net water diversion were -0.32 and -0.57, respectively. Moreover, ηe was estimated under different precipitation and water diversion schemes after water-saving irrigation projects. Results indicated that the reduction of water diversion had a greater effect than the water-saving irrigation projects on ηe. However, water consumption in irrigated land kept at a relatively stable level although water diversion tended to decrease in recent years, which showed the good performance of water-saving irrigation projects.