ABSTRACT Revealing the dynamic mixing of stream water sources is essential for understanding catchment hydrological functioning and informing management strategies, especially in humid East Asian monsoon regions exhibiting high annual precipitation with strong seasonality. This study integrated hydro‐meteorological data with comprehensive water isotopes (δD and δ 18 O) analyses in a typical steep headwater catchment in southeastern China. The dataset combined daily and bi‐weekly sampling with sub‐daily sampling during representative Meiyu (persistent frontal rainfall) and Typhoon rainfall events in 2019. We further quantified the dynamic contributions of different sources to stream water using a Bayesian mixing model (MixSIAR). Results showed that all water sources exhibited synchronous seasonal isotopic patterns, indicating rapid hydrological cycling in this humid environment. Source‐mixing results showed that groundwater was the dominant source, contributing > 40% across all seasons. Precipitation contributions increased significantly to ~26% during the major rainy summer season. Soil water contributions, particularly from deeper layers, showed a continuous increase from spring to winter. Furthermore, event‐scale analysis demonstrated a more rapid and substantial increase in precipitation contributions during the Typhoon event than the Meiyu event. Such differentiated responses were corroborated by the contrasting responses of isotopic signals observed in all water sources during both events. This study quantitatively elucidates dynamic mixtures of water sources at seasonal and event scales, advancing our understanding of the time‐varying catchment response in the humid East‐Asia monsoon climate. These findings offer valuable implications for understanding hydrological responses to typical while contrasting weather conditions, which is fundamental for regional flood risk assessment and water management.
Han et al. (Sun,) studied this question.