Scenario-Based Flood Hazard and Risk Assessment Using Multi-Criteria Analysis in Semarang City

Abstract

This study assessed flood hazard and risk in Semarang City, where increasing hydrometeorological pressures and rapid urban development have heightened flood impacts. An integrated Geographic Information System and multi-criteria spatial modeling approach was applied by combining terrain parameters (slope, height above nearest drainage, distance to stream), hydrological factors (curve number, total precipitation, effective precipitation), and demographic indicators representing social vulnerability. Physical parameters were derived from DEM-based processing and rainfall interpolation, while vulnerability was quantified from population structure, education level, and density. Three hazard scenarios were generated using different weighting schemes, and the resulting hazard layers were multiplied by the social vulnerability index to produce spatially explicit risk maps. Scenario 1 produced hazard patterns more strongly associated with drainage networks and terrain, while Scenario 2 generated more dispersed patterns under the stronger influence of effective precipitation. Scenario 3 formed broader precipitation-driven zones. Flood-risk assessment showed that Scenario 2 had the largest combined High and Very High risk area (13,849.92 ha; 42.00%), followed by Scenario 1 (13,190.40 ha; 40.00%) and Scenario 3 (12,940.01 ha; 39.24%). Validation using 86 ground-referenced points showed the highest model performance for Scenario 1, with an Overall Accuracy of 90.12% and a Kappa coefficient of 0.80, followed by Scenario 3 at 89.53% and 0.79, while Scenario 2 reached 84.88% and 0.70. The results show that changes in parameter weighting alter both spatial risk patterns and predictive performance across Semarang City.