Study On The Relationship Between Surface Evapotranspiration And Soil Water And Salt Content In Yutian Oasis

Evapotranspiration is the main form of surface water expenditure.It determines the balance of surface water and energy,and is an important link in regional hydrological and ecological processes.Taking Yutian Oasis in Xinjiang as the research area,based on the optical remote sensing data and combining the meteorological and hydrological data,the surface albedo,the vegetation index,the surface temperature net radiation flux,the soil heat flux and the sensible heat flux are calculated,and then the evapotranspiration in the region is estimated.In this study,SEBAL model and METRIC model were selected for comparison and verification to obtain the model for estimating evapotranspiration in the study area,and the model was adopted to analyze the spatio-temporal variation of evapotranspiration in oasis.The main research results are as follows:(1)The vegetation coverage rate of the desert area,Gobi area,saline land and bare land in Yutian Oasis is the lowest,the vegetation index is-0.19~0.12,compared with 2011,the vegetation index in 2016 shows a general trend of increase;in the same year,the vegetation index is higher in the same spring,and the fall vegetation index is lower.The surface temperature of oasis is low,and the surface temperature of desert and Gobi in oasis is higher.The distribution of net radiation flux on the surface of Yutian Oasis is basically the same as the surface temperature.The area with high vegetation coverage in the central and eastern part of Yutian Oasis is low,which is negatively correlated with the distribution of the normalized vegetation index(NDVI).(2)SEBAL and METRIC models showed consistency with MOD16-ET product data in the evapotranspiration of 2011 and May 2016 and October.The R2 of SEBAL and METRIC models retrieved from the evapotranspiration in oasis was higher than0.9,which was highly correlated.Therefore,these two models were all applicable to the estimation of evapotranspiration in the study area.(3)in the May 2011 inversion results,the estimation accuracy of the METRIC model is 0.9554,higher than that of the SEBAL model.In May 2016,the same result is found,and the accuracy of the METRIC model is 0.9414,which is higher than that of the SEBAL model.In the results of the October evapotranspiration,the accuracy of the SEBAL model is higher than that of the METRIC model.In October 2011,the accuracy of the SEBAL model is 0.9483 and the SEBAL model is 0.9056.The same results also appear in the evapotranspiration fitting in October 2016.(4)The evapotranspiration in Yutian oasis has obvious regional characteristics.The vegetation coverage of the arable land,woodland and rivers in the middle of the study area is large,and the evapotranspiration is the largest,and the evapotranspiration is the lowest in Gobi and desert areas.From time to time,the surface evapotranspiration of Yutian oasis has obvious seasonal changes.The evapotranspiration in spring is higher in May,and the evapotranspiration in autumn is lower in September.Compared with 2011,the amount of evapotranspiration increased in 2016.(5)there is a linear positive correlation between the evapotranspiration and the soil water content in the study area,and the R2 is higher than 0.8.It shows that the soil moisture affects the Evapotranspiration to a great extent,that is,the higher the regional evapotranspiration is high in the soil surface water content,and the low evapotranspiration of the soil water content is low.(6)evapotranspiration in the study area was negatively correlated with salt content in the soil surface,and R2 was greater than 0.7,showing a significant correlation.It shows that the soil salinity has a great influence on the evapotranspiration,that is,the surface evapotranspiration of the region with high salt content in the soil is smaller and the soil salt content is low,and the surface evapotranspiration is higher.(7)there is a negative correlation between the evapotranspiration of the study area and the pH value of the soil,but the correlation is not strong,and the R~2 is only about 0.5,indicating that the evapotranspiration is not affected by the pH value of the soil.