美联储-洪水风险图与气候信息的分布影响（英）-2023.10-95页_11mb

Summary

Key Findings and Impacts of Flood Risk Mapping

Insights on flood map evolution:

• Incorrect omissions: Since Hurricane Katrina (2005), flood maps rezoned 1.4 million properties out of the high-risk floodplain, primarily in minority neighborhoods. However, five million properties were incorrectly omitted from the high-risk designation, largely due to overlooking rain-based flooding risk.
• Premium distortion: Map updates decreased insurance coverage nationally while reducing perceived flood risk, creating price signals aligned with outdated risk assessments.

Distributional impacts:

• Disproportionate declines in insurance coverage occurred in neighborhoods with higher shares of Black and Hispanic residents, exacerbating pre-existing disparities.
• Premium reductions (emergency buys) and differences in response to mandatory purchase requirements (MPR) reinforced neighborhood-based disparities.

Spatial and insurance impacts:

• Map updates decreased overall flood insurance coverage: 100,000 fewer policies active two years post-update.
• Rezoning inside (outside) the 100-year floodplain increased (decreased) insurance take-up, including indirect spillover effects outside high-risk zones due to belief changes.

Welfare gains and losses:

• Correcting flood maps to reflect current science could increase welfare by $20 billion annually, primarily benefiting wealthier areas.
• However, past map updates distorted risk information, leading to welfare losses spread across income groups.

Policy Implications

Flood risk mapping should consider multiple risk dimensions (pluvial, fluvial, coastal) to provide accurate risk signals. Concerted efforts combining improved flood models, equitable information access, and insurance market design could help mitigate flood risk while promoting equity.