Establishment And Application Of Farmland Water Balance Equation Based On Remote Sensing Evapotranspiration In Yanqi Basin

Evapotranspiration is a key variable in water resources transformation,especially for the spatiotemporalvariation and prediction of crop water consumption in arid regions under the current changing environment.Based on MOD16 data from 2001 to 2019,this paper analyzed the temporal and spatial changes of actual evapotranspiration(AET)and potential evapotranspiration(PET)in the Yanqi Basin,and identified the evolution characteristics of evapotranspiration over the years under the changing environment.Taking remote sensing evapotranspiration as an independent and objective data source,this paper established the annual farmland water balance equation from 2001 to 2019,replaced the traditional algorithm with remote sensing evapotranspiration,and deduced the actual groundwater extraction and its change characteristics in the irrigated area under the condition of the study region length sequence,and to explore the evolution trend of groundwater environment in Yanqi Basin under the strictest water resources management.The main results are as follows:(1)The accuracy of potential evapotranspiration was tested by using the measured pan data from three meteorological observation stations in Yanqi Basin,Yanqi,Hejing and Bohu.The correlation coefficient between the measured pan evaporation and PET reached R~2=0.94.The water balance equation of farmland was calculated in the typical area of Bosten Lake Township buried in underground water depth,and the reliability test of the accuracy of the actual evapotranspiration was carried out.The accuracy of the actual evapotranspiration of remote sensing in this area was more than 80%.The results show that the accuracy of MOD16 evapotranspiration data in the study area meets the requirements.(2)On the interannual scale,the actual evapotranspiration of the Yanqi Basin showed an upward trend,while the potential evapotranspiration showed a downward trend.The spatial distribution of the two showed obvious differences and opposite trends.On the whole,the linear tilt rate of interannual remote sensing evapotranspiration is in a basically unchanged trend.From the perspective of inter-annual fluctuations,the average annual remote sensing evapotranspiration is relatively stable in the past 19 years.According to different land use types,cultivated land,woodland and grassland are relatively stable,and the fluctuation is the largest near water area.(3)Over the years,land expansion has led to the increase of cultivated land area and the increase of total irrigated area,and the increase of water demand in the irrigated area has increased the contradiction between supply and demand of water resources in Yanqi Basin.The number of mechanical Wells and the amount of groundwater extraction have increased accordingly,and the groundwater level has continued to decline,leading to a series of groundwater environmental problems.Therefore,controlling the total amount of evapotranspiration in the basin is an effective monitoring method to reduce the water consumption in the irrigated area.