Applicability evaluation of three improved temperature vegetation dryness indices in High Mountain Asia

Study region: High Mountain Asia (Qinghai-Tibet Plateau and surrounding areas) (HMA) Study focus: Soil dryness and wetness in HMA respond dramatically to global climate change. Monitoring soil moisture can provide a scientific foundation for water security in the plateau, middle, and lower basins. In this study, the applicability of the Temperature Vegetation Dryness Index (TVDI) with three improved protocols was evaluated to rectify the long-standing misuse of the TVDI method for regional drought assessment. New hydrological insights for the regions: The unsuitability of the TVDI in alpine regions was demonstrated by the nonlinear correlation between soil moisture and the TVDI. Among the three improvement schemes, TVDIm (obtained by controlling the temperature variable) best reflected the temporal and spatial distribution of soil moisture in the growing season of HMA, especially for surface soil moisture in the middle-and high-altitude areas. The TVDI, TVDIf (obtained by con-trolling the wet edge), and TVDI_A (obtained by controlling the partition) are not suitable for drought evaluation in medium-and long-term regions because the correlations between the three indicators and soil moisture are inconsistent in space and time. This study provides a new method to identify whether the TVDI can effectively evaluate regional drought. It also provides a more comprehensive reference for monitoring soil moisture and evaluating dryness in alpine regions using optical remote sensing.