New calculations, which takes into account sea-level rise, rainfall and flooding along smaller creeks not mapped federally, estimates that 14.6 million properties are at risk (which is almost double the 8.7 million properties shown on federal government flood maps).
The federal government’s flood maps are used to determine where and how to build, whether homeowners should buy flood insurance, and how much risk mortgage lenders take on.
“Millions of home and property owners have had no way of knowing the significant risk they face,” said Matthew Eby, founder and executive director of the First Street Foundation, a group of academics and experts based in New York City who compiled the data, creating a website where people can check their own address.
Federal flood maps, managed by the Federal Emergency Management Agency (FEMA), have long drawn concerns that they underestimate flood risk.
Part of the problem is keeping the maps up to date, which is not only costly and labor intensive.
In addition, FEMA’s maps aren’t designed to account for flooding caused by intense rainfall, a growing problem as the atmosphere warms.
When FEMA does issue updated maps, mostly everyone objects in order to avoid higher federal flood insurance rates. “You can’t appeal your rate. You can only fight your map,” said Roy Wright, who ran the National Flood Insurance Program until 2018.
The First Street Foundation created its flood model, called Flood Factor, using federal elevation and rainfall data, and coastal flooding estimates from hurricanes. The foundation then checked its results against a national database of flood claims and historic flood paths.
Overall, the results, which cover the contiguous United States — including areas the government hasn’t yet mapped for flooding, and places where the federal maps are decades old — show a vast increase in risk compared with official estimates.
Find your home’s Flood Factor
The National Flood Insurance Program (NFIP) is managed by the Federal Emergency Management Agency and is delivered to the public by a network of approximately 60 insurance companies
How to Purchase Flood Insurance
To purchase flood insurance, call your insurance company or insurance agent, the same person who sells your home or auto insurance. If you need help finding a provider go to FloodSmart.gov/find or call the NFIP at 877-336-2627.
Plan ahead as there is typically a 30-day waiting period for an NFIP policy to go into effect, unless the coverage is mandated it is purchased as required by a federally backed lender or is related to a community flood map change.