41 Million Americans Live in Flood Zones -Three Times the FEMA Estimate, Finds New Study

Flood waters inundated Port Vincent, Louisiana after historic rains in August 2016. 

Flood waters inundated Port Vincent, Louisiana after historic rains in August 2016.  JOE RAEDLE/GETTY IMAGES

The U.S. Federal Emergency Management Agency (FEMA) estimates that 13 million Americans currently live within a 100-year flood zone, areas with a 1 percent chance of flooding in any given year. But a new study published in the journal Environmental Research Letters argues the real number of people exposed to flood risk is about 41 million — more than three times FEMA’s estimate.

FEMA’s flood maps have long been criticized for being outdated and for underestimating flood risk in the U.S., City Lab reported. The study, published last week, used a new high-resolution flood model with updated river, elevation, and rainfall data from U.S. scientific agencies, as well as revised population density maps, to carefully map current flood risk. It identified several large areas previously not thought to be in 100-year flood zones, including along the Pacific coast, across the Midwest, and in cities around the Great Lakes.

“Producing maps the FEMA way essentially misses a lot of flood hazard,” Oliver E. J. Wing, a doctoral candidate at the University of Bristol and lead author of the study, told City Lab. “And these maps are what inform risk management decisions in the U.S. at the moment.” One of the major problems, Wing said, is that FEMA’s methods “tend to ignore smaller streams,” which often run through heavily populated areas.

The research — done by scientists at the University of Bristol in the U.K., The Nature Conservancy, and the U.S. Environmental Protection Agency — also looked at projected population and housing trends in the U.S. to map future flood risk. More than 13 percent of the U.S. population currently resides in the 100-year flood plain, but that number could rise to 15.8 percent by 2050 and 16.8 percent by 2100, the study found. Communities in South Dakota, Nebraska, and New Mexico could see a five-fold increase in flood exposure by 2100. Florida and Texas’s flood risk could triple or quadruple.

The scientists warn, however, that these projections do not take into account climate change and its impacts, such as sea level rise and heavier precipitation events, which they said could put even more Americans at risk of flooding.