Spatiotemporal Variations Of Evapotranspiration And Its Impact Factors Based On Remote Sensing In Xinjiang

Evapotranspiration is a very critical variable in the transformation of water resources,especially for the utilization,management and prediction of water resources in arid areas.This study estimated the evapotranspiration in Xinjiang from 2001 to 2019,based on remote sensing technology using the remote sensing evapotranspiration model,combined with remote sensing,meteorology,DEM,runoff and land use data.Furthermore,it analyzed the temporal and spatial characteristics of evapotranspiration,preliminarily explored the relationship between evapotranspiration,and climate factors,land use changes and vegetation changes,revealed the influence of the temporal and spatial variation characteristics of evapotranspiration on water resources in Xinjiang.The main results are listed as follows:1.Based on the remote sensing evapotranspiration model combined with meteorological data and DEM data,the evapotranspiration in Xinjiang from 2001 to 2019 was estimated.The results were validated by comparing the estimated results with the measured data at the site scale and the calculative ET based on the water balance method.The correlation coefficients between them are more than 0.92,showing that the estimates ET is reliable.2.There is great variation of the ET in Xinjiang from 2001-2019,ranging from 192.77mm to 284.63 mm with the average ET 221.57 mm.The spatial change trends are decrease in west,north and south,increase in east.The spatial of ET in Xinjiang varied greatly,with bigger in north than south,and bigger in west than east.The annual evapotranspiration showed a single peak trend,and the order of evapotranspiration in four seasons was:summer>spring>autumn>winter.The spatial of seasonal ET is the same with the annual ET in spring,summer and autumn,while the ET in winter is very little in the total study area.3.The impacts of the climatic factors on the ET are different among Xinjiang.In the area with higher altitudes,evapotranspiration shows a significant decreasing trend due to the decrease in temperature,sunshine hours,and increase in relative humidity.In the area with lower altitudes,wind speed,precipitation,and temperature have increased significantly,resulting in increased evapotranspiration.Area changes lead to changes in evapotranspiration of different land use types in Xinjiang.Forest land and water area reduction makes evapotranspiration decreased by 52.72 and 11.142 billion m~3,grassland and arable land to expand so that evapotranspiration increased by 8.4 and 6.171 billion m~3.There is a positive relationship between ET and NDVI of Xinjiang,the NDVI of the Yili River Basin,the Aibi Lake Basin and the Wulungu River Basin showed a significant decreasing trend,resulting in a significant decrease in evapotranspiration;the eastern section of the northern foot of the Tianshan Mountains and the edge of the oasis area of the Tarim River Basin showed a significant increase in NDVI,resulting in an increase in evapotranspiration.4.Totally,the amount of water resources in the past 19 years mainly fluctuated.But the distribution of water resources in time and space is uneven,resulting in the surface evapotranspiration demand not met,water resources scarce,and water shortage of different degrees in various river basins.Water consumption in agricultural activities,the main part of water consumption in the basin,is increasing caused by the expansion of crop planting scale and the change of planting structure.In recent years,the expansion of planting scale and the increase in agricultural water consumption due to the adjustment of agricultural structure have exacerbated the water shortage in the basin.