Triple Oxygen Isotope of West China Autumn Precipitation

The isotopic composition has long been used to investigate the factors influencing precipitation, whereas the variations of event-based precipitation isotopes caused by moisture transition and synoptic meteorological conditions remain limited. The triple oxygen isotope composition of precipitation is conceived to track the component of kinetic fractionation in the water cycle. Here, we present triple oxygen (δ18O, δ17O, and Δ′17O) and hydrogen (δD and d-excess) isotopes in event-based precipitation during the West China Autumn Precipitation (WCAP) to evaluate the influence of various moisture sources in the hydrological process. The temporal variations of δ18O, δ17O, and δD reach their maximum values at the onset of the WCAP, when convective precipitation predominates. They then decrease to their minimum values during the mid-WCAP, a period dominated by stratiform precipitation, and finally exhibit an upward trend in the concluding stage. In contrast, the Δ′17O values remain elevated and stable throughout the mid-WCAP compared to the pre-WCAP stages. Our event-based precipitation isotope data, in combination with moisture analysis, reveal a distinct moisture source transition from the West Pacific Ocean to the westerly domain during the WCAP accompanied by the retreat of the Asian summer monsoon from Northwest China.