Today, about 8.7 million properties are located in special flood hazard areas as determined by FEMA Flood Maps, the legal standard used in the US to manage flood plains, determine insurance requirements and premium pricing policies.
But up to 14.6 million properties, nearly 70% more than FEMA's Special Flood Hazard Areas, may be at significant flood risk, according to the First Street model. The discrepancy between FEMA maps and this new information means that some 6 million homeowners may be unaware of their current flood risk, the group says.
First Street found that by 2050, the number of properties with significant flood risk is expected to further increase to 16.2 million.
The problem is already growing urgently, as large areas of the country have been flooded by devastating floods in recent years.
Right now, First Street's flood models show that the states with the highest proportion of properties currently at substantial risk are West Virginia, Louisiana, Florida, Idaho, and Montana.
In the future, changes in precipitation patterns will continue to cause problems for many towns and cities in the interior.
But as the climate changes, the combined threats of storm surges caused by hurricanes and rising sea levels mean that flooding will be more dramatic in coastal areas, according to First Street.
Other deficiencies in FEMA's flood maps have long been recognized, including by the agency itself.
In an email response addressing the First Street findings, David Maurstad, FEMA Deputy Assistant Administrator for Insurance and Mitigation, said: "FEMA is constantly working to improve the production of Flood Insurance Rate Maps in context. of changing conditions. "
Still, these new data shed light on the growing climate risk millions of Americans already face, though many may be in the dark about their personal exposure, experts say.
"This is more evidence showing that our mapping system is not working efficiently and we need to fix it to better understand flooding in the United States," said Dr. Hamed Moftakhari, an assistant professor at the University of Alabama, who studies threats that natural hazards pose to coastal communities.
In addition to its report, First Street is also launching a new interactive modeling system called the "Flood Factor," which will allow potential home buyers to explore current and future flood risk for any property on or off the market in the States. United contiguous.
The tool assigns a Flood Factor score between 1-10, with one being the lowest risk and 10 being the highest, and allows users to explore how a property's flood risk is projected to change in the coming decades.
"Sophisticated investors have bought private flood risk information from for-profit companies for years," Eby said in a press release. "Not only has the First Street Foundation taken this type of data to the next level, using peer-reviewed science, but it is correcting an information asymmetry by providing free access to ordinary Americans."