Nonlinear wind–surge–tide–wave interactions in typhoon storm surges over the integrated urban–channel–bay–coastal system of Macau, China

This study investigates the dominant physical mechanisms governing typhoon-driven storm surges in Macau using a process-based hydrodynamic modelling framework. The model explicitly resolves the coupled effects of wind stress, atmospheric pressure gradients, tidal forcing, and wave radiation stress, and is applied to hindcast two representative extreme events, Typhoons Hato (2017) and Mangkhut (2018). Simulation results indicate that flood severity in Macau is primarily controlled by the magnitude and persistence of elevated water levels within its narrow channel-bay-coastal system. Results indicate that incorporating wave radiation stress significantly enhances simulation accuracy, particularly in capturing peak surge amplitudes in shallow and topographically complex coastal zones, leading to an improvement of up to 3% in the Skill Score. Owing to Macau’s semi-enclosed coastal geometry, this wind-driven setup promotes strong water convergence, accounting for up to 80% of the total water-level setup in most nearshore areas. In addition, wave radiation stress contributes up to 10–40% of the total surge in regions characterised by complex morphology. Strong nonlinear interactions between storm surge and astronomical tides are also identified, capable of amplifying surge peaks by 20–25%, depending on tidal phase and local bathymetry. During the stronger Typhoon Mangkhut, these nonlinear interactions contributed up to 40% of the total surge within the Wanzai Channel. Overall, the results highlight the critical role of nonlinear, multi-process interactions in governing storm surge dynamics within integrated urban-channel-bay-coastal system. This study provides valuable scientific insights for storm-surge hazard mitigation and the enhancement of coastal resilience in typhoon-prone urban environments.