Soil Moisture Retrieval From Remote Sensing And Its Impact On Evapotranspiration In The Plain Area Of Qaidam Basin

Soil moisture is the core content and link of the groundwater-soil wateratmospheric water circulation system, Evapotranspiration(ET) is the important driving force of this system. The study of distribution of soil moisture and its effect on ET from regional scale has great significance on eco-environmental protection in arid areas. Based on MODIS data and GLDAS data, the daily soil moisture from June to September of 2004—2014 was estimated in plain area in Qaidam basin after downscale treatment of 0~10 cm GLDAS surface soil moisture data using Apparent Thermal Inertia(ATI) method. The retrieval results were validated by combination of field measurement and NDVI. Based on the statistical data of 9 meteorological stations in Qaidam Basin, the changes of soil moisture and meteorological data from 2004 to 2014 and the correlation between them were analyzed. Furthermore, the mean daily ET was estimated in 9 drainage basins of plain using the Surface Energy Balance System(SEBS), and the relationship between soil moisture and ET was also analyzed in this study.The result indicated that:(1) The correlation between ATI and 0~10cm GLDAS soil moisture data was good and the determination coefficient R2 is more than 0.66, so we can retrieve soil moisture in Qaidam basin through downscale treatment of GLDAS data using ATI method.(2) The reliability of the results was validated by distribution of Normalized Difference Vegetation Index(NDVI) and the field measurement, the determination coefficient R2 between retrieval result of soil moisture and field measurement is 0.791, and the R2 between soil moisture and NDVI is 0.954. Therefore, it is reliable to retrieve soil moisture in Qaidam basin based on downscale treatment of GLDAS data using ATI method.(3) The lowest average soil moisture in Qaidam Basin is in 2004, while the highest are in 2010 and 2012 with the values of 15.637kg/m2 and 15.661kg/m2, respectively. The soil moisture started to decrease after 2012.(4) The change of soil moisture in the plain area of Qaidam Basin has a certain response on meteorological factors, the higher the temperature, the less precipitation, the greater the wind speed, the smal er the soil moisture.(5) The minimum evapotranspiration in the plain area of Qaidam basin is in 2004 with the value of 0.237 mm. There is a certain increasing trend of ET from 2004 to 2012, and it reached maximum value of 0.746 mm, and the decreases ET trend is found after 2012. The change of the evapotranspiration and soil moisture were almost same temporarily.(6) The daily ET is positively correlated with soil moisture in the plain area of Qaidam basin and the determination coefficient R2 is more than 0.94. However, the correlation between soil moisture and evapotranspiration in four months per year has a large fluctuation, and to a certain extent, it is related to the difference in temperature, wind velocity, precipitation and other meteorological factors.(7) When the soil moisture is less than 13kg/m2, the evapotranspiration is very small and it is close to 0 or equal to 0.