New data reveals hidden chances of surge in U.S.,

Across much of the United States, the flood risk is far greater than government estimates show, new calculations suggest, exposing millions of people to a hidden threat — and one that will only grow as climate change worsens.

That new calculation, 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 from what experts call a 100-year flood, far more than the 8.7 million properties shown on federal government flood maps. A 100-year flood is one with a 1% chance of striking in any given year.

The federal government’s flood maps guide where and how to build, whether homeowners should buy flood insurance, and how much risk mortgage lenders take on. If the new estimates are broadly accurate, it would mean that homeowners, builders, banks, insurers and government officials nationwide have been making decisions with information that understates their true physical and financial risks.

Numerous cities nationwide — as diverse as Fort Lauderdale; Buffalo, New York; and Chattanooga, Tenn. — show the startling gap in the risks. In Chicago alone, 75,000 properties have a previously undisclosed flood risk. And minority communities often face a bigger share of hidden risk.

“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, 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, but further complicated as climate change has worsened the dangers.

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, politicians and homeowners often object, hoping 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. “It turns it into house-byhouse combat.”

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. Many inland areas, including swaths of Appalachia and numerous major cities, saw big jumps.

However, there are exceptions, particularly along the Mississippi River and the Gulf Coast, where the government has more thoroughly studied and planned for floods. There, the federal maps show more buildings at risk than the new model suggests.

First Street said that in some areas, including small municipalities, the model may overestimate flood risk because it doesn’t capture every local flood-protection measure, such as pumps or catchment basins.

FEMA said it welcomed First Street’s initiative, saying it would “complement FEMA’s efforts.”

“We know there is no perfect science to predict flooding,” a spokeswoman said. “The Flood Factor product may help property owners with the critical decisions they must make and purchase necessary insurance.”

On the coasts: Poor areas at risk

Some of the hidden risk is by the shore. In Fort Lauderdale, a city of almost 200,000 people, FEMA puts about 41% of the city’s 55,000 properties in the floodplain. But according to First Street, the figure is closer to two-thirds, or about 13,000 more properties.

“It seems plausible,” said Richard Benton, Fort Lauderdale’s floodplain manager, when shown First Street’s map. He said the maps did accurately show areas that typically flood despite being outside FEMA’s flood maps.

FEMA is in the process of updating Fort Lauderdale area maps, Benton said, adding that some neighboring municipalities have told him that they intend to fight the new maps, out of concern that too many people would have to buy flood insurance. He declined to say which ones.

As with Illinois, the unmapped risk in Florida appears to disproportionately affect minority communities.

In one ZIP Code at the western edge of Fort Lauderdale that is 80% African American, First Street’s data puts more than 42% of properties in the floodplain, while FEMA puts the number at just 6.5%.

When Sasha Forbes bought a house nearby in 2016, she checked FEMA’s database, which said the home wasn’t in a floodplain. But after she moved in, local officials sent her a letter warning that her house was in an area that floods.

“There was no knowledge of that when we were purchasing the house,” said Forbes, a member of the Broward County Climate Change Task Force and a policy expert at the Natural Resources Defense Council, where she works with community groups to make development in cities more inclusive.

Forbes pointed out that Black families tend to be more exposed to flooding because their homes are often built on cheaper land in historically segregated areas.

Investing in flood protection there would be a good start, she said, adding that the public discussion of climate change should address why minorities are more vulnerable in the first place. “We are really silent on the impact of race,” Forbes said.