Local factors or large-scale circulation? An investigation on controls for precipitation isotopes in a coastal monsoonal region, North China

Study region Yellow River Delta (YRD), north China. Study focus Based on event-scale precipitation samples collected over three complete hydrological years at the Gudao site in the YRD, this study systematically analyzed the temporal variation characteristics of stable hydrogen and oxygen isotopes (δD, δ 18 O) in precipitation. We evaluated the influences of local meteorological factors and large-scale atmospheric circulation on isotopic variability, and explored the lagged regulatory effect of equatorial Pacific sea surface temperature anomalies (SSTA, indicated by the Niño 3 index) on precipitation isotopes between the monsoon and non-monsoon seasons. New hydrological insights The controls on precipitation isotopes at the Gudao site in the YRD present significant seasonal differences. Local meteorological factors play a major role in the non-monsoon season, explaining approximately 41% of the δ 18 O variation. In the monsoon season, isotopic characteristics are largely associated with the upstream rainout effect along moisture transport pathways from the Indian Ocean and western Pacific. Monsoon-season δ 18 O has a significant positive correlation with the Niño 3 index at a 2-month lag (r = 0.60, p < 0.05), suggesting a potential lagged modulation of equatorial Pacific SSTA on regional precipitation isotopes. These results provide new observational evidence for understanding seasonal isotopic variations and a scientific basis for interpreting isotopic records and paleoclimate reconstruction in this coastal monsoonal setting.