Soil water is a link between different water bodies. The study of soil water evaporation is of great significance to understand the regional hydrological process, promote environmental remediation in arid areas, and rationalize ecological water use. On the basis of soil water δ²H and δ¹⁸O data from April to October 2017 in the Xiying River basin in the upper reaches of the Qilian mountains, the lc-excess and Craig-Gordon model were applied to reflect the evaporating fractionation of soil water. The results show that the change in evaporation loss drives the enrichment of soil water isotopes. The signal of evaporative fractionation of soil water isotopes at different elevations has spatiotemporal heterogeneity. From the perspective of time dynamics, the evaporation loss of the whole region during the observation period was affected by temperature before July, while after July, it was controlled jointly by temperature and humidity, evaporation was weakened. Soil salt content and vegetation played an important role in evaporation loss. In terms of spatial dynamics, the soil moisture evaporation at the Xiying (2097 m) and Huajian (2390 m) stations in the foothills area is larger than that at the Nichan station (2721 m) on the hillside and Lenglong station (3637 m) on the mountain top. The surface soil water evaporation is strong, and the evaporation becomes weak with the increase of depth. The research has guiding significance for the restoration and protection of vegetation in arid areas and the formulation of reasonable animal husbandry policies.

Studies about the hydrological cycle based on basin or regional scales often ignore the uniqueness of recycling moisture in mountain areas, and little effort has been made to understand the impact of the local recycled moisture on precipitation in mountain areas. We collected and analyzed a series of samples (stable isotope of precipitation, soil water, plant water, runoff, and groundwater) in the Qilian Mountains, northwest of China. Based on the isotopic mixing model, the characteristics of recycled moisture in the Qilian Mountains were evaluated. The results showed that lateral advection moisture is the primary source of precipitation (83.5~98.38%). The contribution rate of recycled moisture to precipitation was higher in the spring, summer, and autumn (2.05~16.5%), and lower in the winter (1.62~3.32%). The contribution of recycled moisture to precipitation in the high-elevation areas (>2400 m) was higher than that in the foothills area (2100~2400 m). The contribution of vegetation transpiration (f_Tr) to precipitation in the east of Qilian Mountain was higher than that of the land surface evaporation (f_Ev). These proved that in the eastern part of Qilian Mountain, the arge-scale water cycle has a greater impact on precipitation in the area. The influence of local circulating water on precipitation dominated in the summer half of the year. Understanding the contribution of local circulating water to precipitation in the eastern part of Qilian Mountain will help us to understand the local hydrothermal conditions better and provide a basis for rationally arranging local agricultural production activities.