Beyond Cost-Effectiveness: How Risk-Based Flood Mitigation Allocation Produces Racially Inequitable Outcomes

Federal disaster assistance programs aim to reduce flood risk through hazard mitigation, yet whether these investments produce equitable outcomes remains unclear. We examine 30-year cost-effectiveness of federally funded home elevations following Hurricanes Katrina and Rita, analyzing how mitigation effectiveness varies across flood return periods and racial groups. Using the IPCC risk framework, we integrated flood depth data, building attributes, federal funding records, and demographic data. Flood risk was quantified as average annual loss (AAL), and mitigation effectiveness was assessed through percentage risk reduction and benefit-cost ratios (BCR).

Results reveal that AAL in high-frequency flood zones (≥10-year) is ten times higher than low-frequency zones (≥200-year). Critically, elevation achieves 95% risk reduction in high-frequency zones but only 53% in low-frequency zones, where severe flood depths exceed elevation heights. White populations are overrepresented in high-frequency zones (disproportionality ratio 1.8–2.1), while non-white populations are overrepresented in low-frequency zones (ratio 1.1). Chi-square analysis confirmed that BCR outcomes differ significantly by race (χ² = 29.04, p < 0.001): 71–72% of low-BCR investments serve non-white majority areas, while 72% of cost-effective investments serve white majority areas.

We do not argue that federal allocation is biased—risk-based efficiency criteria are appropriate. However, this approach produces structurally inequitable outcomes: non-white populations receive investments where elevation is fundamentally less effective. To address this disparity, we applied equity-weighted BCR analysis, demonstrating that incorporating social vulnerability into project evaluation would justify investments in communities currently excluded under efficiency-only criteria. These findings offer a decision-support framework for balancing efficiency with equity in climate adaptation policy.