Seasonal Variations and Controls on Triple Oxygen and Hydrogen Isotopes in Precipitation—A Case Study From Monitoring in Southwest China.

Precipitation δ18O has offered valuable insights into the evolution of the Asian monsoon. Recent researches focusing on precipitation Δ′17O has enhanced our understanding by offering new perspectives beyond those of δ18O, revealing insights into vapor sources and continental recycling. Nevertheless, there remains a lack of interannual triple oxygen isotope data, particularly in the Asian monsoon region. In this study, we analyzed the triple oxygen isotopes and hydrogen isotopes in monthly precipitation samples collected from Chongqing in Southwest China between 2019 and 2022 A.D. Seasonal variations in δD, δ18O, δ17O, and d‐excess values were observed, with lower values during the rainy season and higher values during the dry season, highlighting the impact of changes in moisture sources and local meteorological conditions on seasonal shifts in δD, δ18O, and δ17O. While, mean Δ′17O values were higher in rainy season and lower in dry season. Notably, during rainy season, there is a negative correlation between monthly Δ′17O values and the RH of the vapor source area, as well as a positive correlation with d‐excess. Recalculated Δ′17O values based on RH of oceanic moisture source, are higher than the measured values for this period, indicating the contribution of terrigenous moisture to precipitation in SW China. Precipitation Δ′17O values provide a more precise reflection of changes in moisture source, continental recycling, and evapotranspiration processes that drive water cycling compared Integrating modeling works in future will facilitate the use of precipitation Δ′17O values to quantify the impact of different moisture source on precipitation. Plain Language Summary: In the context of climatic warming, changes in water vapor source areas have substantial implications for the stability of regional water resources. Despite the importance of these changes, few studies have analyzed them using precipitation data from SW China. We conducted monthly measurements of isotopic compositions in precipitation samples collected in monsoonal SW China between 2019 and 2022 A.D. Seasonal variations in δD, δ18O, δ17O, and d‐excess revealed low values during the rainy season (May–October) and significantly higher values during the dry season (November–April). These variations are primarily attributed to different water vapor sources in distinct seasons. Moreover, we observed a negative correlation between precipitation Δ′17O and relative humidity in the source area of the water vapor during the rainy season, suggesting that Δ′17O contains valuable information about the water vapor's source area. Additionally, the relatively higher Δ′17O values observed in the rainy season imply the influence of continental recycling and evapotranspiration processes. Key Points: Characteristics of triple oxygen and hydrogen isotopes in precipitation were analyzed based on a 4‐year monitoring period in Southwest ChinaTriple oxygen isotopes in precipitation serve as indicators of the extent of isotopic fractionation in water vapor between different seasonsChanges in precipitation Δ′17O show a negative correlation with relative humidity from the moisture source area during the rainy season [ABSTRACT FROM AUTHOR]