Report shows millions more Americans face flood risks than previously thought

July 1, 2020

The nonprofit research and technology group First Street Foundation released flood risk data for more than 142 million homes and properties across the country and it showed nearly 6 million more homes are at risk than federal classifications indicate.

The data, based on decades of peer-reviewed research, assigns every property in the United States a “Flood Factor™,” or score from 1 to 10, based on its cumulative risk of flooding over a 30-year mortgage. People can look up a property’s Flood Factor and learn more about its past, present, and future flood risk at, the foundation’s online visualization tool that launched June 29.

While the Federal Emergency Management Agency classifies 8.7 million properties as having substantial risk by being located within Special Flood Hazard Areas, the First Street Foundation flood model identifies nearly 70 percent more — a total of 14.6 million properties with the same level of risk.

The discrepancy exists because the foundation uses current climate data, maps precipitation as a stand-alone risk, and includes areas that FEMA has not mapped.

When adjusting for future environmental factors like changing sea levels, warming sea surface and atmospheric temperatures, and changing precipitation patterns, the foundation’s model finds the number of properties with substantial risk grows to 16.2 million by the year 2050.

“In environmental engineering, there is a concept called stationarity, which assumes that today is going to be like yesterday, and tomorrow is going to be like yesterday,” said Ed Kearns, Ph.D., First Street Foundation’s chief data officer. “This concept used to work, but with a changing environment it’s a poor assumption and no longer does. FEMA’s method assumes stationarity, First Street’s does not.”

The model was developed by more than 80 of the world’s leading hydrologists, researchers, and data scientists from First Street Foundation; Columbia University; Fathom; George Mason University; Massachusetts Institute of Technology; Rhodium Group; Rutgers University; The University of California, Berkeley; and the University of Bristol.

Following a flood, disinfection and wellhead repair may be common needs among well owners. Well relocation and elevation may also be useful and protective. As always, NGWA recommends water well system professionals be used to assess and service wells.

NGWA offers a flooding resource center for homeowners with well systems at Within this site, well owners can connect to certified contractors in their respective communities nationwide, as well as gain knowledge on how to test, tend, and treat well systems, before and after a flooding event.

NGWA also has resources contractors may find helpful in dealing with flooded water wells including the best suggested practice Residential Water Well Disinfection Following a Flood Event: Procedures for Water Well System Professionals and the Water Well Journal® article titled “Responding to Flooded Wells.”