Disentangling controls of multi-scale variability in precipitation stable isotopes at Yadong and Ali on the Tibetan Plateau

Abstract. Understanding precipitation stable isotope variability over the Tibetan Plateau (TP) is essential for identifying moisture sources and assessing climatic responses. However, drivers of daily and synoptic-scale variability beyond the westerlies and Indian Summer Monsoon (ISM) remain poorly constrained in the southern and western TP. Using event-based precipitation isotope data (δ18O and δD) from Yadong and Ali (May 2021–September 2023), we investigate multi-scale variability drivers. Both sites exhibit nearly identical δ18O and δD magnitudes during the monsoon (June–September), while the westerly-dominated season (November–February) shows maximum differences of 12.2 ‰ in δ18O and 118.8 ‰ in δD. Meteorological controls vary seasonally: amount effects dominate during the monsoon (R=-0.28 to −0.32, p<0.05), while temperature effects prevail in the westerly season (R=0.51–0.79, p<0.001). ISM dominates during isotopic convergence, while westerlies drive divergence via distinct transport pathways. Local Meteoric Water Line analysis indicates stronger moisture recycling and sub-cloud evaporation variability at Yadong. On synoptic scales, simultaneous precipitation events reflect coherent ISM influence. Interannual variability is significantly modulated by ENSO, with δ18O enrichment of 2.8 ‰–5.1 ‰ (δD of 39.3 ‰–255.9 ‰) from La Niña to El Niño. During El Niño, weakened Walker circulation reduces ISM transport and enhances the relative contribution of local evapotranspiration. These results offer new constraints on seasonal moisture source transitions and reveal ENSO sensitivity exceeding previous estimates, advancing understanding of atmospheric moisture transport and regional climate sensitivity over the TP.