| The Hetao Irrigation District in Inner Mongolia has an arid continental climate,with a dry climate and a shortage of water resources.Agricultural production in the district is mainly irrigated by diverting water from the Yellow River.Exploring methods based on remote sensing technology to quickly and accurately estimate regional evapotranspiration and irrigation water efficiency is crucial for rational irrigation and water resource management in irrigated areas.In this paper,using the SEBAL model based on the surface energy balance equation,the evapotranspiration in the 2019 crop growing season(April-September)of the Hetao Irrigation District was quantitatively estimated and the characteristics of the temporal and spatial changes were analyzed.Combined with the precipitation and water diversion data in the study area,a calculation method for the effective utilization coefficient of irrigation water in irrigation areas based on remote sensing evapotranspiration is proposed.And estimation of effective utilization coefficients of irrigation water at different spatial scales in the Hetao Irrigation District.The main research contents and results are as follows:(1)In this paper,with the help of ENVI 5.3 and Arc GIS 10.2 software,Landsat8 remote sensing data is processed,and model parameters such as normalized difference vegetation index,surface temperature,and surface albedo are retrieved.The instantaneous evapotranspiration obtained from model inversion was converted into daily evapotranspiration using the evaporation ratio constant method.By analyzing the characteristics of the inverse evapotranspiration distribution,it can be found that:The evapotranspiration in the Hetao Irrigation District shows obvious spatial heterogeneity.The high-value areas are mainly concentrated in the northeast of the irrigation area,and the evaporation is mostly higher than4mm.The low-value areas are mainly concentrated in the southwest of the irrigation area,and the evaporation is mostly lower than 2mm.From the perspective of time characteristics,the average daily evapotranspiration in the Hetao Irrigation District during the growing season showed a unimodal trend,with a maximum value of 5.75 mm/d in July and a minimum value of 3.52 mm/d in September.(2)The evapotranspiration was calculated by using the FAO P-M formula combined with the observation data of the meteorological stations in the study area,and the inversion results of the model in the same period were compared and verified.The results showed that the R~2was 0.81,the RMSE was 0.54mm/d,and the MRE was 10.86%.It shows that the inversion accuracy of SEBAL model is high,which can provide reasonable evapotranspiration estimation for the study area.(3)Correlation analysis was conducted between the daily evapotranspiration retrieved by the model and the main surface parameters,and it was found that the surface temperature had a negative linear correlation with evapotranspiration,with an R~2 of 0.957;NDVI had a positive parabolic relationship with evapotranspiration,with an R~2 of 0.712.The SEBAL model involves many parameters in the process of inversion of evapotranspiration,and different parameters have different influences on evapotranspiration.Studying the correlation between evapotranspiration and main surface parameters can better understand the operation mechanism of the model and improve the inversion accuracy of the model.(4)The land use types in Hetao Irrigation District strongly affect the distribution of surface evapotranspiration,and the evapotranspiration of each land use type also shows significant regional differences.The order of evapotranspiration under different land use types is:water body>forest land>cultivated land>grassland>construction land>wasteland.The higher the vegetation coverage in the study area,the greater the soil water content,and the stronger the evaporation capacity of the underlying surface.(5)Based on the estimated evapotranspiration of the SEBAL model in the irrigation area,combined with water diversion and precipitation data,the difference between evapotranspiration and precipitation is used as the effective utilization of irrigation water to evaluate the irrigation efficiency of the irrigation area.Calculate the effective utilization coefficient of irrigation water in Hetao Irrigation District in 2019η_eandη.Calculated,η_e is0.529 andηis 0.455. |
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