USA - How climate change will increase storm surge flooding in NYC, Miami and D.C.

As climate change warms the planet, drives up sea levels and energizes hurricanes, the arsenal of dangerous impacts delivered by the fierce storms is expected to get supercharged.

Among the most worrisome: powerful flooding from storm surge.

Rising seas and stronger winds mean the punishing waves pushed ashore by tropical storms and hurricanes will make their way farther and farther inland. That inland march would expose a larger swath of the U.S. coast to the kind of flooding unleashed during Hurricanes Katrina and Sandy, and put more people at risk of drowning, the leading cause of death in hurricanes.

An NPR analysis based on modeling from the National Hurricane Center for three critical regions — New York City, Washington, D.C., and Miami-Dade County — found future sea rise alone could expose about 720,000 more people to flooding in the decades to come.

The analysis used three landmark hurricanes — Sandy, Isabel, and Irma — as benchmarks to understand how the impacts of storm surge could grow.

In all three regions, flooding from storm surge that once lingered along the coast travels miles farther inland and grows deeper. By 2080, when sea rise could reach more than three feet, flooding would engulf even more critical infrastructure, including hospitals and schools that often provide shelter.

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New NYC storm surge map shows how climate change threatens affordable housing, upscale waterfront, Gothamist / July 28, 2022

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"Every bit of sea level that we add to this just makes this kind of scenario worse," said Brian Haus, a hurricane researcher at the University of Miami's Rosenstiel School of Marine and Atmospheric Science, who studies the damaging power of storm surge.

Unlike flood waters from rainfall or overflowing canals or rivers, storm surge also carries the power of wind, he said. When a hurricane makes landfall, winds powerful enough to rip a roof off a house push a wall of water onto shore.

"Each time a wave hits, it's just a big spike," Haus said. "That kind of repetitive shock loading is the kind of thing that causes a lot of structural failure."

The National Hurricane Center began testing surge forecasts in 2014 and issued the first official forecasts in 2017, the year Hurricane Irma slammed Florida and triggered the largest evacuation in the state's history.

"Storm surge was killing people more than any other hazard. So they went on this campaign to figure out how can we do something in a way that people understand," said Cody Fritz, who leads the hurricane center's storm surge unit and conducted the modeling for NPR.

Over the years, the center improved its surge model, adding sophisticated layers that provide a more detailed projection of how that water travels over land.

"Realistically, you can zoom down to where the water might be," Fritz said. "We're not that good that we can [locate your] mailbox, but you have a pretty good idea of what risk you might have to deal with."

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