Monitoring the effects of land use and cover type changes on soil moisture using remote-sensing data: A case study in China's Yongding River basin

We used a radiation-transfer equation estimate of July surface temperatures (Ts) in China's Yongding River basin based on thermal infrared Landsat TM images from 1987 and 2005 and Landsat ETM+ images from 2000. Based upon the Ts–NDVI relationship space, we analyzed the scatterplot of Ts versus NDVI to calculate a temperature–vegetation dryness index (TVDI). We used a linear regression model between soil moisture and TVDI to estimate soil moisture to depths of 10 and 20 cm. We produced a land use and cover type map by classification of the Landsat images, and used the map to study the influence of land use and cover type changes on soil moisture. Some areas of farmland in 1987 had been converted into grassland by 2000, and soil moisture mainly increased, with increases ranging from 20 to 60%. From 2000 to 2005, most of the grassland in the northern part of the study area and some grassland in the central area were converted into farmland, and soil moisture decreased by up to 60%. Soil moisture decreased most obviously in areas where forest was converted into grassland, with decreases ranging from 60 to 100% in most areas.