From a global perspective, the stable isotope altitude effect is crucial for understanding climate information. However, the intensity of this effect can be influenced by the source of moisture, particularly in inland mountainous regions where the moisture sources are complex. Different combinations of moisture sources might affect the altitude effect. Focusing on the upper Shiyang River in the northern part of the Qilian Mountains in China, this study calculated the proportion of recycled moisture in precipitation and utilized the HYSPLIT model to determine the source of advective moisture. It explored the characteristics and mechanisms by which moisture sources affect the spatiotemporal variations in precipitation isotope effects within the study area. The findings indicated that: (a) The altitude effect follows a seasonal pattern: winter < autumn < spring < summer, with a reverse effect in winter. (b) As the contribution of recycled moisture to precipitation increases, the altitude effect of stable isotopes weakens, primarily due to the disruptive influence of recycled moisture on this effect. (c) The altitude effect of stable isotopes in precipitation is determined by the direction of the moisture source and its attributes. When the primary source of advective moisture runs perpendicular to the mountain range and the moisture migration speed is slow, the altitude effect is pronounced. Thus, although temperature directly causes the altitude effect, water vapor sources significantly influence it in inland mountainous regions.

The processes of water storage have not been fully understood in different vegetation zones of mountainous areas, which is the main obstacle to further understanding hydrological processes and improving water resource assessments. To further understand the process of soil water movement in different vegetation zones (alpine meadow (AM), coniferous forest (CF), mountain grassland (MG) and deciduous forest (DF)) of mountainous areas, this study monitored the temporal and spatial dynamics of hydrogen- and oxygen-stable isotopes in the precipitation and soil water of the Xiying River basin. The results show that the order of soil water evaporation intensities in the four vegetation zones was MG (SWL_slop: 3.4) > DF (SWL_slop: 4.1) > CF (SWL_slop: 4.7) > AM (SWL_slop: 6.4). The soil water in the AM and CF evaporated from only the topsoil, and the rainfall input was fully mixed with each layer of soil. The evaporation signals of the MG and DF could penetrate deep into the middle and lower layers of the soil as precipitation quickly flowed into the deep soil through the soil matrix. Each vegetation zone's water storage capacity of the 0–40 cm soil layer followed the order of AM (46.9 mm) > DF (33.0 mm) > CF (32.1 mm) > MG (20.3 mm). In addition, the 0–10 cm soil layer has the smallest soil water storage capacity (AM: 43.0 mm; CF: 28.0 mm; MG: 17.5 mm; DF: 29.1 mm). This work will provide a new reference for understanding soil hydrology in arid headwater areas.

Stable isotopes in precipitation can effectively reveal the process of atmospheric water circulation, serving as an effective tool for hydrological and water resource research, climate change, and ecosystem studies. The scarcity of stable isotope data in precipitation has hindered comprehension of the regional hydrology, climate, and ecology due to discontinuities on a temporal scale and unevenness on a spatial scale. To this end, we collated stable hydrogen and oxygen isotope data in precipitation from 842 stations in Eurasia from 1961 to 2022, totalling 51 752 data records. Stable isotopes in precipitation across various regions of Eurasia, as a whole, decrease with increasing latitude and distance from the coast. In the summer, stable isotopes in precipitation are relatively enriched, while in the winter, they are relatively depleted. In recent decades, the stable isotope values of Eurasian precipitation show an overall trend of increasing variation with the advancement of years, which is associated with global warming. Geographical location, underlying surface conditions, seasons, and atmospheric circulation are all factors that determine the characteristics of stable isotopes in precipitation. The dataset of stable isotopes in Eurasian precipitation provides a powerful tool for understanding changes in regional atmospheric water circulation and assists in conducting hydrological, meteorological, and ecological studies in related regions. The datasets are available at https://doi.org/10.17632/rbn35yrbd2.2 (Zhu, 2024).

Ecosystems in arid areas are fragile and are easily disturbed by various natural and human factors. As natural tracers widely exist in nature, stable isotopes can be valuable for studying environmental change and the water cycle. From 2015 to 2020, we took the Shiyang River basin, which has the highest utilization rate of water resources and the most prominent contradiction of water use, as a typical demonstration basin to establish and improve the isotope hydrology observation system. The data in the observation system are classified by water type (precipitation, river water, lake water, groundwater, soil water, and plant water). Six observation systems with stable isotopes as the main observation elements have been built. These include river source region, oasis region, reservoir channel system region, oasis farmland region, ecological engineering construction region, and salinization process region; meteorological and hydrological data have also been collected. We will gradually improve the various observation systems, increase the data of observation sites, and update the data set yearly. We can use these data to research the continental river basin ecological hydrology, such as surface water evaporation loss, landscape river water cycle impact of the dam, dam water retention time, oasis farmland irrigation methods, and the atmosphere, such as the contribution of inland water circulation to inland river precipitation, climate transformation, below-cloud evaporation effect, and extreme climate events, which provides a scientific basis for water resources utilization and ecological environment restoration in the arid area. The data sets are available at https://doi.org/10.17632/vhm44t74sy.1 (Zhu, 2022).