Isotope Variability in Summer Precipitation under the Compound Effects of Moisture Source Conversion and Local Meteorological Dynamics in the Yellow River Delta, North China

Hydrogen and oxygen stable isotopes serve as essential tracers for deciphering atmospheric circulation patterns and driving mechanisms of extreme climatic events. However, their utility in high-resolution climate reconstruction remains constrained by their inherent spatiotemporal heterogeneity. This study conducted event-scale observation on the summer precipitation in the Yellow River Delta (YRD), aiming to better understand the isotopic characteristics and controlling mechanisms. The Local Meteoric Water Line (LMWL) in the YRD exhibited low slope and intercept values, indicating strong influences of sub-cloud evaporation and contributions from continental air masses. Furthermore, pronounced interannual variations were observed in the LMWL, reflecting unstable moisture sources and fluctuating local meteorological conditions. D-excess-based estimation demonstrated pronounced interannual differences in the proportions of losses from sub-cloud evaporation and contributions from locally recycled moisture. The isotopic composition in summer precipitation was negatively correlated with the proportion of low-latitude marine air masses and positively correlated with that of high-latitude continental air masses. The relationships between isotopes and local meteorological variables suggest that the “amount effect” could be an important local factor influencing the isotopic composition of precipitation in the YRD. Global and national isoscape products for precipitation isotopes exhibited deviations of varying degrees in simulating the isotopic variation in the YRD, which may be associated with the complexity of local meteorological conditions and moisture sources. This study demonstrates that relying on single-year precipitation isotopic signatures as the regional context for the hydrological tracing may introduce non-negligible uncertainties in coastal monsoon areas, and indicates that the use of historical data and simulation results of precipitation isotopes requires particular caution.