Stable isotopes reveal soil evaporation and its controlling factors in the Heihe River source area on the northeastern Qinghai-Tibetan Plateau

Study region: The Heihe River source area in the Northeastern Qinghai-Tibetan Plateau, China. Study focus: Soil evaporation, which is a key process in soil water loss, is influenced by various environmental factors. However, the identification of its main drivers on a large scale in alpine mountains remains challenging due to sampling constraints. This study examined the spatial distribution of soil evaporation and control factors during the growing season in the Heihe River source area. New hydrological insights: The results indicated that soil evaporation, represented by lc-excess values, gradually increased from southeast to northwest, and then decreased, reaching a depth of 50 cm below the surface. Although the normalized difference vegetation index explained 54 % of the spatial variation in soil evaporation, the interaction between land surface temperature and soil water content (SWC) provided a more robust explanation. The soil evaporation losses exhibited the following pattern: cropland > grassland > forest land > shrubland. In forest land and shrubland, SWC and precipitation explained 68 % and 73.3 % of the spatial variations in soil evaporation, respectively. Grassland mainly relied on temperature and SWC, with 49.33 % of unexplained spatial variability by environmental factors. Meanwhile, the aridity index and aspect explained 45 % and 44.6 % of the spatial variations in cropland. These findings provided invaluable information for advancing our understanding of the ecohydrological processes in alpine mountains.