Estimation of moisture availability over the Liudaogou river basin of the Loess Plateau using new indices with surface temperature

This study presents developments of indices for surface moisture condition estimations aiming at a more mechanistic approach compared to previous indices. Moisture availability (ma), calculated as the ratio of actual evapotranspiration (ET) to reference evapotranspiration (ET0), and soil water content were estimated over a river basin on the Loess Plateau of China using two newly developed indices. A modified temperature–vegetation dryness index (MTVDI) was calculated from satellite-derived surface temperature, and aerodynamic minimum and maximum surface temperatures estimated from meteorological data. MTVDI corresponded well to seasonal variations of ma over an area of varied land use, and especially well in areas of grassland. A wet-edge index was derived from the relationship between MTVDI and the normalized differential vegetation index (NDVI), the MTVDI–NDVI triangle space, which is achieved by plotting MTVDI as a function of NDVI. The wet-edge index showed the relationship to ma of various land surfaces and soil water contents in the river basin. However, we concluded that a wider range of vegetation cover and soil moisture content were needed to calculate a meaningful wet-edge index. These two indices have advantages that can estimate surface moisture condition qualitatively. They can be used as aridity and/or drought indices.