Water Use Performance For Irrigation Area Based On Distributed Hydrological Model

Water use performance for Irrigation Area is evaluated through some water use efficiency indicators, such as canal water utilization coefficient, irrigation water use coefficient and water use productivity. It is inappropriate to extend the result of small scale to big scale because of the spatial variability and water reuse, which causes the scale effect of irrigation water use efficiency indicators at different scales. In addition, it is available to obtain the water balance factors and crop production at different scale using the distributed hydrological model. Therefore, this paper proposed a new water use evaluation index system according the problem of irrigation water use efficiency evaluation. Then, the distributed hydrological model of JieFangzha Irrigation Area was constructed using SWAT to obtain water balance factors and crop yield at different scale. After that, water use productivity of different scales was analysed based on the simulation of water balance items and crop yield. The main research contents and results for this study are as follows:(1) Firstly, basic data were provided for the calibration and validation of distributed hydrological model in irrigation areas throught carrying out experimental research of water cycle in different scales and observation of crop yields and water balance elements in Liberation gate irrigation—a typical irrigation district in northern China. Combined with IWMI water balance calculation framework, irrigation water use efficiency evaluation index system was proposed to do research on variation of water use efficiency indicators in different scales.(2) Secondly, based on the principle of the distributed hydrological model (SWAT), evapotranspiration and crop growth module processes were focused on to analyse the lack of the simulation of water cycle in application of irrigation areas. In order to using SWAT be suitable for water cycle simulation in shallow groundwater irrigation, a "bottom-up" approach was adopted to add groundwater evaporation to soil moisture circulation.(3) Thirdly, irrigation distributed hydrological model was established to analyse the application of SWAT model. First, LAI was used for Calibration crop growth parameters which indicated that the value of BLAI of irrigated crops was highly large. Then, for the target variable runoff and ET performed, LH-OAT and SUFI-2were used to analyse sensitivity which showed that the sensitive parameters on runoff mainly concentrated in soil and groundwater and that regional evapotranspiration process mainly affected by evaporation, soil and crop vegetation. Based on the sensitivity analysis results, SUFI-2algorithm was used for the calibration and validation on runoff and ET. In addition, the proportion of crop yield simulation and actual values were around the1:1which further validated the reliability of the model and the rationality of parameters.(4)Fourthly, using the main drains as the main line and gradually nested way from upstream to downstream, eight scales were separated from the study area. With2011as the base year, the spatial distribution of water balance elements were simulated and analysed under the status mode of irrigation. The results showed that the larger amount of irrigation water use in upstream and the smaller in downstream resulted in the flowing from upstream to downstream which caused that lower water table is shallow and that the evaporation of diving is large. So the variation in soil moisture is very small. The water efficiency evaluation index variation on different scales was anlysed using the water balance elements and crop yields of last eight scales obtained from model simulation. The results showed that for different crops, the trend of WP1and WPg fluctuated increasd when the scale increased, and when reached a certain scale level (approximately400km2-600km2), the trend remained flat or slightly declining. Due to the ratio of water consumed by crop evapotranspiration basically the same under different scales, WPETremained stable. The trend of DRF8and DRFa firstly kept stable or slightly increased, when reaching the critical dimension (approximately200km2-300km2), with the increase of the scale the trend increased firstly and then decreased finally.