Robust Portfolio Prioritization of Fire-Risk Mitigation Actions in Vulnerable WUI Settlements: A Case-Informed Decision Framework for El Olivar, Chile

Fire-risk mitigation in vulnerable wildland–urban interface (WUI) settlements is a portfolio problem: warning, evacuation, fuel management, dwelling hardening, and spatial interventions are complementary yet compete for limited implementation resources. This study develops an auditable portfolio decision framework and applies it to public-document evidence for El Olivar, Viña del Mar, Chile. Six actions are represented by evidence-bounded ordinal envelopes for risk-reduction relevance, feasibility, time to initial benefit, and resilience to delayed external access; implementation-resource demand is imposed as a hard constraint rather than a compensatory criterion. A binary portfolio model is evaluated under equal, rank-order-centroid, unrestricted-simplex, and ordered-simplex preference structures using 200,000 uncertainty realizations without assuming equal spacing between ordinal categories. Under the baseline normalized implementation requirements (1–3 additive planning units, not monetary costs), routes/maps plus decentralized warning has a portfolio-acceptability fraction of 89.2–95.3% at B=2. At B=4, vegetation-fuel management joins that core, with a portfolio-acceptability fraction of 66.7–91.5%. These fractions quantify robustness of optimal selection across the defined admissible evidence and preference inputs; they are not empirical probabilities of intervention effectiveness, fire-loss reduction, or implementation success. Structural actions enter mainly as resources expand, while cluster-scale compartmentation remains limited by transferability to attached-housing morphology. The framework identifies staged bundles conditional on stated evidence, preference, and resource assumptions rather than a universal action ranking.