Controls on daily to interannual variations of summer precipitation isotopic signatures from Qinghai Lake watershed, northeastern Tibetan Plateau

Numerous crucial paleoclimate records in monsoon regions depend on past precipitation isotopes as proxies for hydroclimate; however, the relationship between climatic variability and precipitation isotopes remains poorly understood. In this study, we investigated key climatic drivers from local to regional scales using 7-year-long daily summer precipitation isotopes in the Qinghai Lake watershed of the northeast Tibetan Plateau, located in the margin of summer monsoon extent. Results showed that daily precipitation delta O-18 and delta H-2 exhibited intra-seasonal fluctuation from 2012 to 2018 characterized by low isotopic values in July (e.g., delta O-18 = - 10 parts per thousand) and high values in June (e.g., delta O-18 = - 6.7 parts per thousand). Moisture source analysis via Hybrid Sing-Particle Lagrangian Trajectory indicated that the primary moisture of Qinghai Lake was mainly derived from northwestern inland regions, North China, and South China across seasons with high specific humidity and trajectory frequency, having a great influence on the isotopic patterns in precipitation across seasons. Moreover, convective activities in the primary moisture source regions, shown by outgoing longwave radiation and specific humidity along back trajectory, played a crucial role in controlling the seasonal variability of precipitation isotopes. These effects could be closely associated with the upstream convective intensity over the moisture sources or the changes of moisture sources during the observation periods. Interannual precipitation delta O-18 variation was significantly correlated with the indices of the El Nino Southern Oscillation (r = 0.63, p < 0.1), with high precipitation delta O-18 value in the dry El Nino year of 2015. Our findings suggested that precipitation isotopes in the Qinghai Lake watershed represented a spatial-temporal integrative indicator of precipitating processes and convection activity, providing the interpretation of paleo-isotope data in the regional hydroclimate variability across monsoon-affected regions.