Development of a climate-adaptive flood defence index to support planning and design decisions

ABSTRACT Climate change is increasing uncertainty in flood defence infrastructure (FDI) planning and design, challenging conventional approaches based on historical conditions and fixed design thresholds. This study develops a Climate-Adaptive Flood Defence Index (CAFDI) as a practical decision-support framework for assessing barriers and enabling conditions influencing climate-adaptive flood defence. The framework considers five dimensions: governance and policy, financial feasibility, technical capacity, stakeholder engagement, and hydro-physical conditions. Stakeholder assessment scores are integrated with the Analytic Hierarchy Process (AHP) to calculate separate barrier (CAFDI-B) and enabler indices (CAFDI-E), while Fuzzy Synthetic Evaluation (FSE) provides complementary dimension-level assessments. The framework is demonstrated using 92 stakeholder responses from Australia (41) and Vietnam (51), recruited through purposive and snowball sampling. Using equal weighting across the five top-level dimensions, the Australian sample recorded barrier and enabler scores of 3.531 and 4.274, respectively, compared with 3.460 and 4.014 for the Vietnamese sample. Although both samples exhibited substantial barrier conditions and strong enabling conditions, they differed in their priority dimensions and decision determinants. The proposed framework provides a transparent and adaptable approach for diagnosing climate-adaptive flood defence priorities and supporting planning and design decisions across different institutional and environmental contexts.