The First National Flood Risk Assessment Defining America’s Growing Risk

Publication Date

June 29, 2020

Page Number


Link to Report




A national and state-by-state flood models presented are the “culmination of decades of research and development” from “a multitude of resources and techniques”  that “builds on previously peer-reviewed scientific research.” The model was produced in partnership with researchers and hydrologists from First Street Foundation; Columbia University; Fathom; George Mason University; Massachusetts Institute of Technology; Rhodium Group; Rutgers University; The University of California, Berkeley; and University of Bristol.  The model is to be used by policy makers and individual property owners alike. These results are being made publicly available through a new tool, Flood Factor™, a “free source of probabilistic flood risk information.”

The results “indicate significantly more flood risk across the U.S. when compared to standard flood risk tools, nationally across the contiguous United States.” The model generally captures around 1.7 times as many properties at risk as the Federal Emergency Management Agency (FEMA) Special Flood Hazard Area (SFHA) designations.  5.9 million properties and property owners are currently unaware of or underestimating the risk they face because they are not identified as being within the SFHA zone. The inclusion of pluvial flood risk, sea level rise, and ungauged streams are responsible for most of this additional risk. 2.6% (3.6mil) of properties face an almost certain risk of substantial flooding in the next 30 years. 10.3% of US properties face a substantial risk of flooding in that period.

“When adjusting for future environmental changes, by 2050 the number of properties with substantial risk across the country will increase by 10.9% to 16.2 million. Louisiana (69.7%), Delaware (21%), New Jersey (19.1%), Florida (18.6%), and South Carolina (16.7%) rank highest for the greatest proportional increase of properties with significant risk over the next 30 years.”

In-depth profiles are provided for each state, incorporating factors such as:

  • Changes in risk to properties between 2020-2050
  • How much greater the number of properties are at risk versus FEMA estimates
  • How each state’s flood risk compares to others and the national average
  • Greatest number and proportion of properties at risk along with the greatest growth in risk by city or town
  • Flood history and protection, including top protection measures, e.g., levees

The report has implications for individuals, the insurance industry, and governmental agencies at all levels.

Note: This report integrates well with the on-going efforts of the American Society of Civil Engineers (ASCE) to assess the infrastructure of the United States. The ASCE’s 2017 Infrastructure Report Card gave the United States an overall grade of D+. 

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