By Seth Borenstien, Associated Press

 More than 17 million people along the U.S. Atlantic and Gulf coasts are at the highest risk of 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 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 risk of extreme flooding, while 20.5 million were at high risk, the second-highest level.

They found many vulnerabilities in the eight highlighted cities, from Houston, which flooded during Hurricane Harvey in 2017, to New York, which was inundated during Hurricane Sandy in 2012.

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 does not mean that 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 coauthor Wanyun Shao, a climate scientist at the University of Alabama.

“Just look at the magnitude,” Shao said. “Those numbers are shocking, 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.

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