Resurgences after storm surges in the Beibu Gulf: Process studies of Typhoon Yagi (2024) and multi-decadal statistics

Storm surges and subsequent resurgences present severe, multi-phase flooding hazards. This study investigates these processes within the Beibu Gulf using a combination of numerical simulations from the Coastal and Regional Ocean COmmunity model and an analysis of long-term tidal gauge observations. The model successfully hindcasted the complex hydrodynamics induced by Typhoon Yagi (2024). The post-landfall non-tidal residuals exhibited oscillations within two frequency bands: a lower frequency band with a period of approximately 40 h, and a higher frequency band around tidal frequencies driven by tide-surge interactions. Spatiotemporal and transect analyses across the basin revealed that the resurgence during Typhoon Yagi is a basin-scale phenomenon governed by a shelf seiche mechanism. Furthermore, a multi-decadal analysis utilizing a 23-year hourly dataset from the Beihai tidal gauge demonstrates that 67.9% of severe storm surges in this region were followed by pronounced secondary resurgences. These findings establish the prevalence of resurgences after storm surges in the Beihai Gulf and reveal that shelf seiches serve as a possible driver. The insights gained from this study provide a critical reference framework for enhancing marine disaster forecasting accuracy and strengthening coastal zone risk management.