New study finds 'alarming' high flood risk for 17 million Americans on
Atlantic and Gulf coasts
[April 23, 2026]
By SETH BORENSTEIN
WASHINGTON (AP) — More than 17 million people along the U.S. Atlantic
and Gulf coasts are at the highest risk of being affected by flooding,
with New York and New Orleans standing out, according to one of the most
comprehensive studies ever of flood risk.
Researchers at the University of Alabama used 16 different factors
including the geographic hazards, the population and infrastructure
exposed and the vulnerability of people living there. They then brought
in past damages from the Federal Emergency Management Agency's database
and applied three different artificial intelligence tools to figure out
flood risks from Texas to Maine, calculating that 17.5 million people
were at “very high” risk and an additional 17 million were at “high"
risk, the next level.
The authors looked at all sizes of flooding and examined separately what
FEMA considers the most extreme, which are the top 1% of events. The
study found 4.3 million people along the coasts to be at the highest
level of risk of extreme flooding, but 20.5 million to be at high risk,
the second highest level.
They found a lot of vulnerability, highlighting eight different cities
from Houston, which flooded in 2017’s Hurricane Harvey, to New York,
which was inundated in 2012’s Superstorm Sandy.
Wednesday's study in the journal Science Advances found that New York
City has 4.75 million people at the two highest risk levels for all
flooding, with more than 200,000 buildings likely to be damaged.
And while the number of people at risk in New Orleans is far lower,
about 380,000, it involves 99% of the city's population. That doesn't
mean 99% of the people will be affected in the next hurricane or
nontropical flood, but that they might be depending on the storm's
individual path and rain pattern, said study co-author Wanyun Shao, a
climate scientist at the University of Alabama.
“Just look at the magnitude,” Shao said. “Those numbers are shocking,
are alarming.”
The elderly and poor are most at risk
“When the next big storm hits New York City, when the next Hurricane
Katrina -like hurricane makes landfall in New Orleans, people will get
hurt, especially those socially vulnerable populations,” Shao said
referring to the poor, the elderly, children and the uneducated.
Shao and outside experts said the numbers stunned them even though they
were familiar with the worsening effects of climate change.
“New York is known to be susceptible to floods and it has the largest
population. But the fact that New York has nearly an order of magnitude
more flood-exposed population than any other city is surprising,” said
Alex de Sherbinin, a geographer who directs Columbia University’s Center
for Integrated Earth System Information. He wasn’t part of the study.
Flood problems are becoming more frequent in New York and New Orleans
because of human-caused climate change, the study said.
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Two vehicle on Olive Street are flooded during Hurricane Francine in
New Orleans, Sept. 11, 2024. (David Grunfeld/The Times-Picayune via
AP, File)
Other cities are also threatened
Jacksonville has 679,000 people at high or very high risk of
flooding, while Houston is just behind at just under 600,000. Other
cities highlighted include Miami, Norfolk, Virginia, Charleston,
South Carolina, Mobile, Alabama.
Shao and outside experts said what separates her study from others
is the sheer comprehensiveness of all the factors it considers,
including sinking land and pavement that doesn't allow water to seep
into the ground, as well as incorporating human social vulnerability
such as poverty and age.
“This could be applied to other places in the world, such as
Manila,” said University of Virginia engineering professor
Venkataraman Lakshmi, who heads the hydrology section of the
American Geophysical Union, referring to the capital of the
Philippines. He wasn't part of the study, but said the flooding
problems it highlights will get more frequent and intense due to
human-caused climate change.
Columbia University's Marco Tedesco, who wasn't part of the study,
said "it reinforces the crucial concept that future flood disasters
are not just about water—they are about where people live, how
cities are built, and who is least protected.”
Actions can lessen the risk
De Sherbinin said, "the analysis of the flood risk factors is
important for local planners, emergency managers, and even highway
crews and utility providers. We all know that low lying areas are
more flood prone, but the data they have assembled provide more
insights into flood risk, particularly for flash floods.”
Study lead author Hemal Dey, a geospatial scientist, said he hopes
local officials look at not just building more dams and levees, but
more natural infrastructure such as wetlands, grasslands, rain
gardens and estuaries.
“The research is solid confirmation of what emergency managers have
been saying for years. Realtors will hate it,'' said Craig Fugate, a
former FEMA director who wasn't part of the study. "The harder
question is what we’re actually going to do about it."
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