Disentangling climate change and urbanization effects on future tropical cyclone compound flood hazards

Tropical cyclone-induced compound flooding poses a growing challenge for low-lying coastal megacities, as climate change and continued urban development may further intensify these hazards. Yet most planning frameworks and hazard assessments remain anchored in historical extremes, failing to account for how future conditions may fundamentally reshape disaster potential. Here, we examine how the impacts of Super Typhoon Mangkhut (2018)—one of the most intense storms to strike the Greater Bay Area (GBA)—could change under future climate and urbanization conditions projected for SSP5–8.5, using a Pseudo-Global Warming (PGW) framework with high-resolution atmospheric and storm surge models linked through one-way forcing. Our results show that future warming substantially delays typhoon weakening during the critical landfall period, sustaining central pressure ~ 5 hPa lower and increasing rainfall intensity within 200 km of the typhoon center by ~27%, with a ~ 12% rise in storm surge. In contrast, projected future urbanization, with a transition towards taller and more compact urban forms, has a much smaller and more model-dependent additional effect on rainfall and storm surge (~1%). The integrated Compound Hazard Index (CHI) increases by ~19% on average under climate change alone and by ~21% when urbanization is included, further demonstrating the dominant role of climate change in the projected increase in compound hazard. By providing a case-study assessment of compound flood hazards associated with an extreme typhoon under a high-emissions future climate scenario, this study offers actionable insights for redesigning urban resilience strategies in a warming and urbanizing world.