Human mobility amplifies compound flood risks in coastal urban areas under climate change

This study investigates how human mobility patterns affect compound flood risks in coastal urban areas, focusing on Kowloon, Hong Kong. Traditional flood risk assessments often rely on static population data, failing to capture daily fluctuations in exposure due to movement between residential and commercial areas. To address this, the researchers developed a dynamic flood risk assessment framework that integrates time-sensitive population data with hydrodynamic flood modeling. By simulating 75 scenarios involving varying rainfall and storm surge intensities under both current and future climate projections (to 2100), the study highlights how urban exposure shifts throughout the day and week, revealing more nuanced risk profiles.

The findings show that flood risk significantly varies across time and land use. Residential areas face heightened nighttime risk, while commercial zones are more vulnerable during the day. Weekday risks show greater fluctuation than weekends, especially under future climate scenarios. Sea level rise and extreme rainfall are shown to intensify compound flood hazards, particularly near coastal zones. The study introduces the Night-Day Risk Ratio (NDRR) to quantify these temporal dynamics. Overall, it emphasizes the need for adaptive, time-sensitive flood risk strategies that account for both physical and human-driven risk factors in urban planning.