Variation characteristics of stable isotopes in precipitation and the environmental factors that influence them in the Shiyang River Basin of China

Stable isotopes in precipitation are used to understand the hydrologic cycle as well as changes in climate. Based on 274 precipitation samples collected from 6 stations in the Shiyang River Basin from July 2013 to June 2014, the variation characteristics of stable isotopes and their response to the environment contribute to the understanding of the hydrologic cycle in an arid region of Northwest China. Stable isotopes in the Shiyang River Basin vary significantly with the seasons. Compared to the winter months, the slope and intercept of the Local Meteoric Water Line (LMWL) are lower and the values of δ18O and δD are higher in the summer. The variations of δ18O and δD in precipitation are significantly affected by temperature, elevation, and sub-cloud evaporation, but are not affected by precipitation on an annual scale. The effects of temperature are more pronounced in the summer than in the winter. Isotope variations are weakly affected by precipitation amounts during the summer, especially in July, from both greater precipitation and continuous precipitation. The concentrations of δ18O and δD decrease with height at rates of − 0.3‰/100 m and − 2‰/100 m, respectively. In the summer months, the values of δ18O and δD at the surface are greater than those at cloud base, indicating that the variations of stable isotopes are influenced by sub-cloud evaporation. In general, higher values of Δ18δ and Δ2δ are related to higher temperatures, less precipitation, and lower relative humidity, with the reverse also being true. The variations of stable isotopes and the environmental factors that influence them differ with meteorological conditions and geography.