Quantifying time-dependent flood resilience index in a densely populated urban environment in Manado, Indonesia

Flooding poses significant risks, with severe physical, economic, and psychological impacts. Efforts to mitigate flood risk include improving predictability, developing flood control structures, and enhancing community resilience. Flood resilience indices (FRIs) quantify a community's characteristics regarding prevention, preparedness, response, and recovery aspects around flood events. This study uses a time-dependent FRI in nine wards in a densely populated urban environment at the flood-vulnerable riverbank communities in Singkil Subdistrict, Manado, Indonesia. The FRI considers the temporal flood event propagation, physical vulnerability, and demographics reflecting the community's resilience to flood. The time-dependent FRI is quantified and applied for three flood return periods, 2, 20, and 100 years. Flood discharge was simulated using HEC-HMS, with results input into HEC-RAS for flood scenario modeling. FRI was then assessed using HEC-RAS flood propagation results for the event phase and national socio-economic data for the flood recovery phase. The study captures the community's immediate responses and near-term adaptations, where resilience differs by location and fluctuates across the flood scenarios. Most of the wards have the characteristics of rapid FRI decrease caused by the sudden onset of the incoming flood and a more gradual recovery of the FRI. Comparison between the three return periods shows slight FRI curve differences, indicating that the relatively high probability of 2-year floods is already significantly damaging the community. These findings prompt a call for location-specific, effective and time-sensitive flood mitigation strategies, especially in densely populated vulnerable wards in urban environments.