Flood Injustice in 500-Year Floodplains: Researchers Shed Light on Intersection of Flood Risk and Social Vulnerability

Researchers from Utah State University have conducted a study analyzing the impact of flood injustices in inland urban areas, particularly in the Intermountain West region of the United States. The study, published in the Frontiers in Human Dynamics journal, focuses on the intersection of flood risk and social vulnerability at the microscale. The researchers used data from the National Flood Hazard Layer and the American Community Survey to quantify flood injustices in Salt Lake County, Utah, and identified household and population flood injustices.

Key Takeaways:

• Urban flooding presents a global challenge, disproportionately affecting socially vulnerable communities, with an annual average cost of US $4.5 billion and an average of 17 fatalities per year between 1980 and 2024.
• FEMA's outdated 100-year floodplain delineations fail to capture evolving flood risk, leading to development inside and outside of 100-year floodplains and potentially higher flood risk for vulnerable communities.
• The cities of Millcreek and South Jordan emerge as most vulnerable for 500-year flood injustices, with flood risk ratios of 1.92 and 1.67, respectively.
• The study contributes to a deeper understanding of flood injustices in inland urban areas, shedding light on the intersection of flood risk and social vulnerability at microscales.
• Identifying flood injustice communities can inform targeted interventions and policy measures to mitigate flood injustices and enhance flood resilience and adaptation in inland urban areas for vulnerable communities.
• The researchers developed a straightforward and easily implementable approach for city and county level planning and flood injustice policymaking.

Statistics:

• The annual average cost of flood damage is US $4.5 billion.
• There are an average of 17 fatalities per year due to floods between 1980 and 2024.
• 44% of Salt Lake County's 500-year floodplain is in the City of South Salt Lake.
• The cities of Millcreek and South Jordan have flood risk ratios of 1.92 and 1.67, respectively.
• The study analyzed data from the National Flood Hazard Layer and the American Community Survey.

Sources:

• "Flood injustice in 500-year floodplains." Frontiers in Human Dynamics, 2025,7. The publisher for Frontiers in Human Dynamics is Frontiers Media S.A.
• "Researchers from Utah State University Detail Research in Social Science (Flood injustice in 500-year floodplains). Science Letter. May 16, 2025; p 1163.
• National Flood Hazard Layer data
• American Community Survey data