Disaster risk management of tidal inundation in coastal Surabaya: A spatial and institutional approach

Coastal urban areas in Southeast Asia are increasingly vulnerable to tidal inundation due to climate change, land subsidence, and inadequate infrastructure. Surabaya, a rapidly growing coastal city in Indonesia, faces recurrent tidal flooding, particularly in its northern districts. This study aims to evaluate the spatial distribution of tidal flood risk and assess the alignment between hazard exposure and institutional capacity. Using an integrated spatial-institutional framework, a GIS-based hazard model was developed through cost distance analysis, incorporating elevation, slope, and land use data. These hazard layers were overlaid with socio-economic vulnerability and community capacity indicators to construct a composite risk index. The results reveal that approximately 30% of Surabaya's land area is exposed to tidal flood risk, with subdistricts such as Kenjeran, Krembangan, and Semampir identified as high-priority zones due to their combination of high vulnerability and low institutional capacity. Institutional analysis, based on planning documents, stakeholder interviews, and preparedness indices, highlights gaps in coordination, technical capacity, and data integration. This study advances the field by introducing a novel integration of cost distance-based hazard modeling with locally grounded resilience indicators (IKD and IKM), which has not been previously applied in coastal flood studies. The analysis uncovers a unique spatial-institutional mismatch - areas categorized as low hazard but constrained by weak governance capacity - thus extending the Pressure and Release (PAR) model in the context of rapidly urbanizing coastal cities. Beyond Surabaya, this framework provides a replicable and transferable approach for Southeast Asian coastal regions facing similar interactions of climate hazards, land subsidence, and fragmented governance.