From Flood Hazard to Actionable Urban Resilience: Scenario-Aware Building, Road, and Evacuation Planning for Derna, Libya

Abstract

The September 2023 Derna disaster has already generated high-quality flood reconstruction and remote-sensing damage studies. This paper shifts from retrospective damage detection to a scenario-aware decision-support framework for reconstruction and evacuation planning using official Copernicus EMSN177 5-, 100-, and 500-year flood products. We recompute scenario capture, marginal exposure density, mitigation effectiveness, and residual exposure from the technical-report statistics. The potentially exposed population is 6,945, 10,555, and 11,310 of 72,922, while exposed buildings are 4,236, 5,148, and 6,059. The 100-year envelope already captures 93.3% of the population and 85.0% of the buildings exposed under the 500-year case. Expanding from 5 to 100 years adds 3,610 people and 912 buildings (3.96 people per additional building), whereas 100 to 500 years adds only 755 people and 911 buildings (0.83 people per additional building). After the modelled mitigation package, exposed population falls to 4,939, 7,842, and 8,161, reductions of 28.9%, 25.7%, and 27.8%. These results support the 100-year envelope as a minimum risk-informed redevelopment buffer and the 500-year envelope for strategic siting of critical facilities and evacuation redundancy.