兰德-Analysis-to-Support-Louisianas-Flood-Risk-and-Resilience-Program-and-Application-to-the-National-Disaster-Resilience-Competition_38页_8mb

Summary of Louisiana's Flood Risk and Resilience Program Analysis

Core Content

This document presents a quantitative analysis conducted by RAND to support the State of Louisiana's application to the U.S. Department of Housing and Urban Development (HUD) National Disaster Resilience Competition (NDRC). The study focuses on evaluating nonstructural flood risk mitigation projects in three coastal parishes: Plaquemines, Lafourche, and Terrebonne. The objective is to determine the most cost-effective way to allocate the available funds to elevate residential structures and reduce flood risk, using data and models developed for Louisiana's 2017 Coastal Master Plan.

Main Views and Key Information

Flood Risk Context

• Hurricane Impact: Despite improvements in levees following Hurricane Katrina, coastal Louisiana remains at significant risk from storm surge flooding. Hurricane Isaac (2012) caused $2.39 billion in damages and 34 lives lost.
• Projected Damage: Without mitigation, annual damages from coastal storm surge flooding could rise from $2.4 billion in 2011 to $23.4 billion in 2061 under a less optimistic scenario.
• Current Flood Risk: The 2012 Coastal Master Plan identified areas at risk due to coastal flooding, which are used as the basis for this study.

Nonstructural Mitigation Strategy

• Elevation as a Measure: Elevating residential structures above potential floodwaters is a nonstructural mitigation strategy that reduces flood damage.
• Base Flood Elevation (BFE): The study uses current 100-year flood depths as the BFE, with an additional two feet of freeboard.
• Participation Rate: An 80% participation rate is assumed for structures that would benefit from elevation.
• Feasibility Threshold: Structures that would need to be elevated higher than 14 feet above ground level are deemed infeasible and excluded.

Project Variants and Budgets

• Budget Ranges: The State defined budgets for each parish: low ($50–$75 million), medium ($75–$100 million), and high ($100–$125 million). A no budget limit option was also considered.
• Project Variants: Multiple project variants were evaluated based on different selection criteria and elevation standards, aiming to optimize flood risk reduction.

Decision Support Tool

• Functionality: The tool allows users to visualize flood risk, project costs, and the number of structures mitigated in different areas.
• Comparison Metrics: Users can compare different project variants using Net Present Value (NPV) and Benefit-Cost Ratio (BCR).
• Flexibility: The tool supports a composite criterion that includes flood depth, socioeconomic data, and cost-effectiveness, enabling more informed decision-making.

Key Findings

• Lafourche Parish: Few structures are cost-effective for elevation due to existing structural protection systems and high projected flood depths in other areas.
• Terrebonne and Plaquemines Parishes: These parishes have a higher proportion of low to moderate income (LMI) households and more potential for nonstructural mitigation.
• Cost-Effectiveness: The State's recommended project provides higher benefits than costs in each parish, with benefits and costs being lowest in Lafourche.
• Prioritization: The composite criterion allows for more nuanced prioritization of areas for mitigation, considering flood risk, LMI populations, and cost-effectiveness.

Methodology

• CLARA Model: A flood risk model used to estimate flood depths and economic damages. It incorporates data from the U.S. Geological Survey, HUD, and FEMA.
• Vulnerability Metrics: Four vulnerability metrics were considered:
  • Current 100-year flood depths
  • Future (Year 50) 100-year flood depths
  • Percentage of LMI households
  • Number of repetitive loss (RL) and severe RL properties
• Selection Criteria: Five selection criteria were used to define project variants, including:
  • Current flood depths only
  • Future flood depths only
  • LMI percentage only
  • RL and severe RL properties only
  • Combined criterion (flood depth, LMI, and cost-effectiveness)
• Cost Estimates: Costs are calculated per square foot based on elevation height, including design, engineering, surveying, and construction activities.

Limitations and Considerations

• Scenario Dependency: The analysis is based on a single plausible scenario from the 2012 Coastal Master Plan, which may not reflect all possible future conditions.
• Static Data: Some data inputs, such as historical RL and LMI data, are treated as static, despite the expectation of future changes.
• Policy Flexibility: The methodology allows for adjusting mitigation strategies based on different policy preferences, such as prioritizing LMI areas or regions with repetitive losses.

Conclusion

The study provides Louisiana with a decision support framework to evaluate and prioritize nonstructural flood risk reduction projects. It emphasizes the importance of using a composite criterion that integrates flood risk, socioeconomic factors, and cost-effectiveness to guide investment decisions. The findings highlight the need for targeted mitigation efforts in areas with high flood risk and significant LMI populations, particularly in Plaquemines and Terrebonne parishes.

Appendices and References

• Appendix: Tabular results by block group for low, medium, high budgets, and no budget limits.
• References: Includes sources from the 2012 Coastal Master Plan, FEMA, HUD, and other relevant studies.

Key Terms

• CLARA: Coastal Louisiana Risk Assessment model
• BFE: Base Flood Elevation
• LMI: Low to Moderate Income
• RL: Repetitive Loss
• NPV: Net Present Value
• BCR: Benefit-Cost Ratio