Spatio-temporal Distribution Characteristics Of Oasis And Evapotranspiration In Lop Nor

Xinjiang Uygur Autonomous Region,located in the northwest of China,is the most sensitive region to climate change.Because it is located in the hinterland of the continental plate and the ecological environment is extremely fragile,the climate is extremely dry.Lop Nor area is short of water resources and precipitation,low vegetation coverage,oasis is not only the production place of local residents,but also the habitat of animals.Evapotranspiration is one of the components of regional hydrological balance,it is also an important reference value in water resources planning.Therefore,it is of great significance to study the distribution of oasis and evapotranspiration on different spatial and temporal scales and its influencing factors in this region in the design of water conservancy projects,reconstruction of ecological environment and protection of biodiversity.Therefore,based on the MODIS and AVHRR data of continuous series,this paper estimates the NDVI(Normalized Difference Vegetation Index)and actual evapotranspiration of Lop Nor area,Xinjiang from 2000 to 2018 by using SEBS(Surface Energy Balance System)model and penman Monteith formula.This paper analyzes its changing trend on the scale of time and space,and discusses its influencing factors and degree,the results are as follows:(1)In space,the vegetation coverage in the study area is poor,with the distribution pattern of high in the west,low in the east,high in the north and low in the south,and the distribution law of the center area is the lowest.During the study period,the NDVI of the study area showed an increasing trend year by year,and its change is negatively correlated with temperature,and not significantly correlated with precipitation,but the overall trend was consistent.(2)The spatial distribution of actual evapotranspiration in the study area is:northern region > western region > eastern region > central region > southern region.In terms of interannual variation,the actual evapotranspiration in the study area showed an obvious upward trend;In terms of seasonal variation,the actual evapotranspiration from large to small was summer,spring,autumn and winter.The actual evapotranspiration in winter was very small,almost zero.Temperature and precipitation have obvious influence on the change of actual evapotranspiration.Wind speed,sunshine hours and relative humidity also have certain influence.(3)The trend of potential evapotranspiration in the study area is decreasing year by year.By analyzing the relationship between actual evapotranspiration and potential evapotranspiration,it can be concluded that the phenomenon of "evaporation paradox" appears in the study area.The potential evapotranspiration in the study area is mainly affected by relative humidity and wind speed.(4)In the study area,there is a significant positive correlation between vegetation coverage and actual evapotranspiration in spatial and temporal scales.Shrubbery is the most obvious land cover type affecting evapotranspiration in the study area,followed by high coverage grassland.