兰德-Adapting-Land-Use-and-Water-Management-Plans-to-a-Changing-Climate-in-Miami_112页_8mb

Summary of "Adapting Land Use and Water Management Plans to a Changing Climate in Miami-Dade and Broward Counties, Florida"

Core Content

This report examines the vulnerability of Miami-Dade and Broward Counties, Florida, to the impacts of a changing climate, particularly focusing on groundwater flooding and saltwater intrusion. It presents an integrated modeling framework to assess how current and future land use and water management plans can be adapted to mitigate these risks while supporting economic development and ecosystem protection.

Main Objectives

• To improve the region's capacity to adapt to climate change and land use changes.
• To better understand the costs of both action and inaction across a range of future scenarios.
• To develop a transparent, interactive, and technically credible decision support tool for evaluating vulnerabilities and potential adaptation strategies.

Key Findings

Vulnerability to Groundwater Flooding

• Both counties are vulnerable to coastal flooding, and this vulnerability is expected to increase by 2040 under various sea-level rise (SLR) scenarios.
• Inland areas are also at risk of flooding, and this risk may be exacerbated under future rainfall scenarios.
• Asset values at risk from inland groundwater flooding are projected to increase significantly by 2040 due to future development and climate impacts.

Broward County

• Currently vulnerable to tidally induced groundwater flooding due to low surface elevations.
• Future changes in precipitation could increase or decrease groundwater depth across the county.
• Under the highest SLR scenario, groundwater depth could decrease by up to 2 feet in some coastal areas.
• Approximately $12 billion in assets are vulnerable under current conditions, and this value is expected to rise by 22% to 45% by 2040.
• Orienting development toward traffic analysis zones reduces future vulnerable assets by 45% compared to elevation-based scenarios.
• Remaining vulnerability is concentrated in three to four areas, offering targeted adaptation opportunities.
• Saltwater intrusion could impact wells with replacement costs up to $250 million under the least favorable future.

Miami-Dade County (UMD)

• Less vulnerable to tidally induced groundwater flooding than Broward, with only a few areas experiencing groundwater depths less than 1 foot.
• Vulnerable assets under current conditions are estimated at $2.1 billion, significantly lower than Broward.
• Vulnerable asset values are expected to increase between 25% and 270% by 2040 due to development and climate impacts.
• Directing growth toward higher ground reduces vulnerable assets by 19% compared to non-elevation-based scenarios.
• About half of the vulnerability to groundwater flooding occurs only under the high SLR scenario.
• Saltwater intrusion is not projected to impact groundwater wells in UMD by 2040.

Approach and Methodology

• The report uses the Robust Decision Making (RDM) method to evaluate vulnerabilities under multiple climate and land use scenarios.
• An integrated modeling framework was developed to simulate rainfall, drainage, infiltration, and recharge across the region.
• The framework connects hydrological outputs with economic data to provide a hydrological-economic vulnerability analysis.
• Three methods for distributing future population and asset growth were tested:
  • Random distribution
  • Elevation-based distribution
  • Traffic Analysis Zone (TAZ) based distribution

Uncertainties Considered

• Sea-Level Rise (SLR): Three SLR scenarios were evaluated.
• Rainfall patterns: Five rainfall scenarios were derived from 112 projections.
• Population and asset growth distribution: Three methods were tested to model the spatial allocation of future development.

Key Strategies and Levers

• Land use planning: Future development patterns can significantly influence the exposure of assets to groundwater flooding and saltwater intrusion.
• Adaptation measures: Including retrofitted and new facilities to control salinity, reduce drainage volumes, and mitigate flooding.
• Economic planning: Incorporating data on asset values and replacement costs to inform cost-benefit analyses.

Importance of Stakeholder Engagement

• The report emphasizes the need for stakeholder engagement and decisionmaker interaction to ensure that adaptation strategies are realistic and effective.
• Local and regional officials, planners, engineers, and residents are the primary audience, and the findings are also relevant to other coastal regions in the U.S. and globally.

Conclusion

• The region faces significant challenges due to rising sea levels and changing precipitation patterns.
• A well-coordinated and adaptive approach to land use and water management is essential to reduce risks and protect public values.
• The integrated modeling framework provides a valuable tool for long-term planning and decision-making, and further refinements are recommended to enhance its effectiveness.

Recommendations

• Incorporate commercial districts and public infrastructure into economic risk analyses.
• Treat future land use and asset growth as uncertainties in any vulnerability or adaptation assessment.
• Continue and refine the decision support tool for broader application in Southeast Florida.
• Implement targeted adaptation measures in areas most vulnerable to flooding and saltwater intrusion.

Acknowledgments

The report acknowledges the support of the John D. and Catherine T. MacArthur Foundation, as well as the contributions of county officials, planners, and researchers in Miami-Dade and Broward Counties. It is dedicated to Charles Zwick, a long-time supporter of RAND, who passed away before the report's publication.

References

• The report draws on previous RAND studies, including those on robust decision making, stormwater management, and coastal planning.
• Data and models were developed in collaboration with the South Florida Water Management District and the U.S. Geological Survey.

Figures and Tables

• Figure S.1: Integrated Modeling Framework
• Table 2.1: XLRM Matrix
• Table 2.2: Potential Goals and Metrics
• Table 4.1: Monthly Scaling Factors for the Five Future Rainfall Scenarios
• Table 4.2: Standardized Land Use Categories
• Table 5.1: Strategies to Mitigate Groundwater Flooding for Broward and Miami-Dade

This report provides a comprehensive assessment of climate vulnerabilities in Southeast Florida and offers actionable insights for policymakers and planners to adapt land use and water management strategies in response to a changing climate.