Study On The Evolution Of Vegetation Coverage And Evapotranspiration In Oasis Irrigation Area Based On Remote Sensing

Oasis,as a desert and semi-desert area,has both natural and human characteristics.Vegetation is an important part of the oasis ecosystem and environment.Surface evapotranspiration is one of the important links in the recycling and distribution of oasis water resources.Constrained by various conditions such as regional climate change,human activities,soil quality,topography,and water resources,vegetation coverage and evapotranspiration evolution laws can reflect the overall status of the regional ecological environment quality.This paper takes Shule County as the research area,based on the 6th Landsat series(TM/ETM+/OLI)remote sensing image data from 1995 to 2020,using NDVI pixel binary model and SEBAL model to efficiently save water in Shule County and its farmland.Research on the evolution of vegetation coverage and daily evapotranspiration before and after reconstruction.The main conclusions are as follows:(1)From 1995 to 2020,the vegetation increase in Shule County was generally carried out by the method of infilling and peripheral expansion with high vegetation coverage.In the past 26 years,the vegetation coverage area has shown an increasing trend,and the increase in cultivated land area is the main reason for the increase in vegetation coverage in Shule County.In 2005,the total vegetation coverage area was the smallest(1149.5 km~2),and in 2020,the total vegetation coverage area was the largest(1574.6 km~2),an increase of 425.1 km~2,an increase of 37.0%.The average vegetation coverage and the average NDVI both show a gradual upward trend,and the rising rates from 1995 to 2020 are 55.4%and 115.4%,respectively.(2)There are temporal and regional differences in the spatial change of vegetation coverage in Shule County.During the period of change,the vegetation coverage of Shule County improved most significantly from 2010 to 2015 and 2015 to 2020(a period of efficient and water-saving irrigation area reconstruction of farmland).In terms of changing areas,the vegetation coverage degradation in Shule Town(county town)and the Baza area of various towns is the most significant,the vegetation coverage in the northwest of Alabu Township,the east of Taheqi Township,the central and northeast of Yamanya Township,and the northern part of Tazihong Township The improvement of coverage into a large area is the most typical.The transfer between different coverage levels is mainly the transfer of bare land or very low and low coverage to medium and high coverage,the transfer between medium coverage and high coverage,and the bare land or very low,low and medium coverage eventually turning to high coverage..(3)From 1995 to 2020,the vegetation coverage of high-efficiency water-saving farmland in Shule County has shown an increasing trend over the years.As the area of vegetation coverage increases,the vegetation coverage also continues to increase,especially after the implementation of high-efficiency water-saving(The rate of increase in 2010-2020)is greater than the rate of increase in the period before the implementation(1995-2005).The transfer of vegetation coverage is mainly from extremely low coverage to small proportions of low,medium coverage and large proportions of high coverage,low coverage to small proportions of medium coverage and large proportions of high coverage,and medium coverage to high coverage.Coverage shifted mainly.(4)Based on the SEBAL model,reverse the daily evapotranspiration of Shule County during the six periods from 1995 to 2020.The simulation results verify that the error is within a reasonable range,and the time of the daily evapotranspiration in Shule County And spatial change analysis.The average daily evapotranspiration for the 6 periods were 4.01 mm,3.78 mm,3.50 mm,4.77 mm,4.01 mm and 3.89 mm,respectively.It reached its maximum value in 2010,and gradually decreased after the implementation of high-efficiency water saving(2010-2020).Combined with the comparative analysis of the spatial distribution map of land use types,it can be seen that the watersheds and water areas with sufficient water and basically stable surface temperature in Shule County have the largest daily evapotranspiration;the bare land or unused land areas with very low vegetation cover have the smallest daily evapotranspiration.The main contributor to the increase in vegetation coverage is the increase in the area of arable land.Large areas of unused land are converted to arable land.During 2010-2020,arable land will be implemented with high-efficiency water-saving irrigation technology.This may be due to the gradual decrease in daily evapotranspiration during this period.main reason.(5)On the basis of the daily evapotranspiration in Shule County,the spatial distribution map of daily evapotranspiration during the six periods from 1995 to 2020 was obtained by cutting out the efficient water-saving boundary map of the farmland from 2012 to 2017.The average daily evapotranspiration in the six periods were 3.91 mm,3.86 mm,3.49 mm,4.93 mm,4.49 mm,and 3.95 mm,which reached the maximum in 2010,and showed a downward trend during the implementation of high-efficiency water-saving irrigation technology in farmland from 2010 to 2020.