Abstract: Estuaries are economically developed and storm-prone regions where the maximum storm tide level(MXST) is governed by cross-scale coupling among storm surge, astronomical tide, and river flood, while large-scale human activities reshape morphological-hydrodynamic patterns. Understanding storm-tide response mechanisms under the altered morphological regime is crucial for storm-tide risk management. Focusing on the Bay-Inlet-Channel(BIC) system of the Pearl River Estuary, as the core region of the Guangdong–Hong Kong–Macao Greater Bay Area(GBA), this study used Typhoon Hato(2017) as a representative event and applied a Delft3D model to examine changes in the MXST before and after intensive human disturbance(1960s and 2020s). In response to the narrowed and deepened morphology, the MXST increased slightly in the Bay(up to 0.22m, 9%), remained nearly unchanged at the Inlet, and increased substantially in the Channel(up to 0.51m, 21%). Factor decomposition showed that MXST responses were dominated by surge-contribution changes(which accounts for 40~105% of MXST variations), with the largest increase in the Channel(0.46m, 90% of the MXST variation), whereas the influences of astronomical-tide(−30~35%) and nonlinear-interaction(−20~50%) contributions were smaller. Mechanism analyses indicate that reclamation-enhanced convergence amplified storm surge in the Bay, causing the slight increase in MXST; offsetting effects among human activities and the energy regulation functions of the Inlet maintained MXST stability; and dredging-induced depth increase weakened bottom friction in the Channel, enhancing both surge and astronomical-tide contributions and thereby dramatically lifting the MXST. Under a “Triple Coincidence” scenario with stronger flooding, increased flood and nonlinear-interaction contributions jointly raised MXST by up to 0.26m(9%), exacerbating storm-tide risks.

Key words: Maximum storm tide level, Bay-Inlet-Channel, human activities, morphological evolution, response mechanism