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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.

"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."

Five years ago, Hurricane Irma aimed its mighty force at Miami, putting the nation's seventh-most populated county in the crosshairs of one of the most powerful storms on record.

"It was clear that basically everything east of U.S.1 would be under nine feet of water, which includes my house," said Brian Haus, the University of Miami researcher who studies the damaging impacts from storm surge. "This would have been the complete worst-case scenario for everything in South Dade [County]."

Instead, the storm swerved left and crossed the Lower Keys, sparing the crowded coast from the worst of its flooding.

But what if Irma had stayed its course? As seas rise, storm surge projections modeled by the National Hurricane Center suggest the scenario Haus feared could become dramatically worse. It's a particularly urgent threat for the low-lying southern end of the county, where fast-growing suburbs are squeezed between two national parks and a shrinking farming community.

Using an array of data including wind speeds and other atmospheric conditions during Irma, as well as topography and other features onshore, the National Hurricane Center modeled the depth and extent of flooding Irma would have produced had the center of the storm made landfall in Miami-Dade County.

Fritz, the center's storm surge chief, then added the latest sea level rise projections for the coming years from the National Oceanic and Atmospheric Administration (NOAA) to depict worsening storm surge.

Flooding already at lethal levels under today's conditions would top nine feet farther and farther inland as waters rise. An NPR analysis using 2020 Census data found the number of people at risk could nearly double by 2080, based on NOAA's likely sea level rise projection of just over 2.5 feet.

After Hurricane Andrew swept through in 1992 and decimated the area, South Florida has continued to see repeated strikes or near-misses by tropical storms or hurricanes. Yet construction in the county has boomed almost non-stop.

Developments like Crystal Cay, Silver Palms and Pine Vista replaced tomato fields and marshes. According to data from the University of Florida, 52 percent of developed lots in the area of southern Miami-Dade County pictured in the map below have been built since Andrew. That's more than 44,000 out of about 85,000 parcels with structures.

Of that post-Andrew construction, just over a third is already vulnerable to flooding from a storm like Irma. By 2080, nearly two-thirds (28,000) of those recently developed lots will be at risk.

When a powerful storm comes, "Nothing to do but sit there, and pray and wait."

A U.S. Air Force base and nuclear power plant would be among the critical facilities hit by the surge. The plant's reactors are elevated about 20 feet above sea level, but roads needed to carry diesel fuel and other supplies to a shuttered plant would be under more than nine feet of water.

Black residents in South Florida would be three times more likely to be flooded, a higher rate than the rest of the population, according to an analysis by Tampa Bay Times data editor Langston Taylor.

The tiny village of Cutler Bay would be one of the many places to bear the full brunt of the surge. Just this past June, flooding from what would become the first named storm of this year's hurricane season submerged parts of the town, including Craig Emmanuel's street.

"You went to sleep on dry land and you woke up and the streets were flooded," said Emmanuel, who nearly missed his son's fifth grade graduation. "I don't think anyone was prepared for it to be as high as it was."

In nearby Richmond Heights, where Emmanuel grew up and his parents rebuilt their house after Andrew, flooding could be between six feet and nine feet deep in just four decades. The historic black community, built after World War II for returning vets, sits more than five miles from the coast.

And that kind of inland flooding can complicate evacuation plans. State emergency managers say it would take about a day to evacuate coastal neighborhoods. When flooding reaches inland communities, evacuation times more than triple.

Tim Meerbott, Cutler Bay's mayor and a lifelong resident, helped found the village in 2005 partly to help recover from Andrew, a storm he rode out hiding in his garage with his family.

"We didn't have near as many residents back then. We didn't have near as much concrete back then," he said. "Andrew had 165 mile an hour sustained winds and you're up to your shoulders in water. What do you do? Nothing to do but sit there, and pray and wait."

Superstorm Sandy was the deadliest storm of the 2012 hurricane season. Over 48 hours, it damaged or destroyed nearly 800 buildings across New York City, including 70,000 housing units and left about 2 million people without electricity. Forty-three people in the city died as a result and damage was estimated at $19 billion. The preparation and response was one of the largest mobilizations of public services in history, according to the city.

The consequences of a similar storm in the future could be even worse.

With rising sea levels, the National Hurricane Center's model predicts that the extent and depth of storm surge will grow dramatically across the five boroughs. NPR's analysis found that the number of New Yorkers directly threatened by flooding could more than double from about 207,000 in 2020 to 468,000 in 2080.

Superstorm Sandy slammed 35 public housing developments managed by the New York City Housing Administration (NYCHA), leaving tens of thousands of low-income New Yorkers without power. Other types of affordable housing were hit hard, too: about 24,000 apartments were in the path of the storm surge, according to data from New York University's Furman Center.

Claudia Perez lives in the Washington Houses in East Harlem and is president of the residents' association. She recalled watching the floodwaters surge around the local hospital.

"Sandy was really scary," she said. "When you see a hospital going underwater, you're like, 'Oh my God, what's going on here?' "

Future storms, coupled with sea level rise from climate change, will flood even more low-income New Yorkers' apartments, exacerbating an ongoing affordable housing crisis. An NPR analysis of data from the National Hurricane Center (NHC) predicts that a Sandy-like storm could flood more than 50 NYCHA developments by 2080.

Nationally, one study projects three times as many low-income homes at risk of frequent flooding by 2050.

"People in affordable housing are more exposed to flooding, and they have the least resources to deal with it," said Bernice Rosenzweig, a professor of environmental studies at Sarah Lawrence College.

Disasters often leave a legacy that involves a struggle to adapt with the resources left behind. In East Harlem, for example, Sandy's floodwaters damaged parts of Metro North Plaza and the East River Houses, two NYCHA developments. Both received funding from the Federal Emergency Management Agency (FEMA) for repairs and upgrades, which are still in progress.

The nearby Washington Houses were outside Sandy's main inundation zone, so it wasn't eligible for the same FEMA-funded resiliency upgrades. But the NHC data predicts that, as early as 2050, a comparable storm could bring floodwaters to the development's door, putting residents and infrastructure at risk.

Million dollars homes built in storm surge zones

Across the East River in Brooklyn, upscale neighborhoods also are at risk. The blue door for the El Pinguino oyster bar sits on Greenpoint Avenue, a few steps from the luxury tower-studded skyline of the waterfront.

Owner Nicholas Padilla has come to dread the rain. At any given time in his dirt basement, Padilla can dig about six inches deep and hit water.

Padilla's first restaurant in the area, Alameda, was flooded with six feet of water and raw sewage by Sandy, costing him tens of thousands of dollars in damages, shortly after he had signed the lease. But he won't leave until the flood waters chase him permanently from his business and his home, located less than a block away. He doesn't know where else to live.

"It's New York City. It's so hard to find somewhere to go. It just feels like people will just live here until it's in the river," Padilla said.

Several parts of New York City's waterfront, including the neighborhoods of Greenpoint and Williamsburg in Brooklyn, are booming with development. The local community board estimates that 40,000 residents were added to both waterfront areas in the past decade — many in new high-rise towers right along the East River. Despite sea level rise, this property ranks among the most valuable in the city — with median sales around $1.2 million last year.

Over the next 30 years, tide and storm surges will bring damaging flooding here at a frequency that will be more than 10 times as often as it does today, according to other data from NOAA.

Advocates and environmental experts are urging the city, state and federal government to prepare its housing stock for coming storms. Some are calling for building upgrades, so New Yorkers aren't trapped in powerless, hazardous apartments and houses the next time the storms arrive. Others say the time to depart is now.

"We can't control the ocean, not even with sea walls," said Dr. Klaus Jacob, a geophysicist and climate expert at Columbia University's Climate School. "We need to start moving people to higher ground now, and using the coastal areas as a barrier."

With Hurricane Isabel still churning off the coast of North Carolina, on Sept. 18, 2003, Washington, D.C., and federal officials decided to shut down the nation's capital. Metro trains and buses stopped running more than 12 hours before the storm hit the city, and 350,000 federal workers were told to stay home.

The storm blew into the District in the middle of the night, with winds of up to 65 miles per hour, pushing a bulge of water up the Potomac and Anacostia Rivers from the Chesapeake Bay.

The Potomac crested at 11.3 ft. above normal – beating the previous storm surge record from 1933. Flooding and downed trees caused an estimated $125 million in damages in D.C., according to the National Weather Service, with millions more in the surrounding suburbs in Maryland and Virginia.

But unlike the other examples in this story, most of the flooding occurred on waterfront parks, including parts of the National Mall, the grassy expanse near the White House dotted with monuments.

In coming decades, as the Potomac and Anacostia rivers rise because of climate change, more areas will be inundated by storm surge flooding. But even in 2080, with sea level three feet higher or more, waterfront parks would absorb the brunt of flooding from storm surges, leaving most homes and businesses dry.

According to the National Hurricane Center's storm surge models and NPR's analysis of 2020 Census data, just 2,100 Washingtonians are likely to be threatened by an Isabel-like storm in 2080, up from 600 people in 2020, due to sea level rise. That's a relatively small number of people in a city of nearly 700,000.

A 150-year-old federal park building frenzy

"D.C. got lucky," says David Ramos, who teaches graphic design at American University and has studied and mapped Washington's historic waterways.

Without intending to, early D.C. planners built in a degree of resilience to the waterfront. It started in the late 1870s, when the Army Corps of Engineers began dredging the silted-up Potomac, where Ramos says "a giant, smelly mudflat" had formed near the White House – a consequence of deforestation upstream and a lack of sanitation in the city.

The Army Corps built new land with the dredged up muck, creating miles of new shoreline. This reclaimed land is now the most at-risk for flooding in the city.

Ramos says the river dredging project happened to coincide with a federal park-building frenzy – the results of which can be seen in the expansive green spaces of today's National Mall.

"Most of the American cities that had big amounts of landfill decided to build housing or businesses on it," Ramos says. In D.C., the vast majority of new riverfront land became parks, nowadays managed by the National Park Service.

"There was no thought at the time about resiliency, withstanding flood damage and things of that sort," says historian John Wennersten, who has authored several books about D.C. waterways. "It was creating more land space for the development of what they called 'monumental Washington,' between 1890 and 1920. Inadvertently, it offered a modicum of protection against storms and tidal surges."

In addition to this "inadvertent" protection, the federal government also constructed a levee system to protect agency headquarters located in low-lying areas downtown.

D.C. also lucked out in terms of geography: the city is farther inland than many East Coast cities, and it is located on the fall line – the place where the coastal plain transitions to higher, hillier land. Much of the city is built on the uphill side of the fall line.

Increasing pressure to build in areas that will flood

In today's Washington, the few riverfront areas that aren't parks are among the fastest growing neighborhoods in the city, as developers turn old industrial areas into luxury apartments and condos.

"The city is not going to stop building," says Meredith Upchurch, with the D.C. Department of Energy and Environment. "We still need to be using a lot of those areas for residential housing, for commerce. People want to be near the river – it's a very desirable place."

The city is updating floodplain regulations to account for rising sea levels, which Upchurch says will more than double the number of buildings considered flood prone and subject to flood-proofing requirements.

And while D.C. "got lucky" in terms of storm surge flooding, compared to other East Coast cities, it's still at high risk from other types of flooding that are being made worse by climate change.

The worst floods in recent years, says Upchurch, have been caused by interior flooding, when a storm dumps more rain on the city than storm drains can handle. Unlike storm surges, there is little to no warning for these events, and flooding can happen miles from a river.

"The storms are just more frequent, more intense and more unpredictable," Upchurch says, noting severe interior flooding has occurred in D.C. in 2018, 2019 and 2020.

According to climate modeling conducted by the city, this type of flooding will only get worse. What is now considered a 100-year storm (with a 1-in-100 chance of occurring in any given year) is projected to be a 15-year storm by 2080 – more than six times as likely to occur.

In a worst-case scenario, interior flooding could coincide with a storm surge, and even with flood waters coming from upstream in the Potomac watershed. In fact, that's what officials were preparing for in 2003 – why the entire city shut down ahead of the storm. Forecasters warned of up to 12 inches of rain; after Isabel passed through, less than an inch had fallen on the city.

"If it looks scary, it is"

Looking to the future, climate and hurricane experts say the nation needs to seriously rethink how it inhabits such vulnerable areas. Early planners unwittingly spared the nation's capital. But in bustling regions like New York and South Florida, catastrophic hurricanes have done little to slow growth in areas where risk becomes more dangerous and more costly. In South Florida alone, future sea rise could nearly double the number of structures in the path of flooding.

"The hardest part with disaster planning is that it's just so difficult to imagine," said Katherine Hagemann, Miami-Dade County's adaptation manager. "I think a lot about this worst case scenario. But that's not the way that most people live."

And that's where the hurricane center thinks it can help. The agency ultimately hopes to replicate the modeling along the entire U.S. coast, said Cody Fritz, the hurricane center storm surge chief.

"When you raise the sea level, it will change the game in terms of the hazard of storm surge," Fritz said. "If it looks scary, it is."

Methodology

The projections of storm surge used in this story were produced by the Storm Surge Unit at the National Hurricane Center. The researchers provided models of possible storm surge under three different sea level rise scenarios — Intermediate-Low, Intermediate, and Intermediate-High — which are possible depending on how climate change unfolds. For the analysis and maps in this story, NPR used the storm surge models based on the Intermediate sea level rise scenario. The storm surge models have intrinsic uncertainty, and NPR excluded storm surge flooding of less than 1 foot from the maps and analysis because it falls within the likely margin of error. For more information on the sea level rise scenarios, see the National Ocean Service's 2022 Sea Level Rise Technical Report.

The hypothetical track for Irma is based on a forecasted track from the actual storm in 2019.

To project how many people could be directly threatened by storm surge, NPR used 2020 Census data to analyze how many people live within the projected inundation zone for each time step. The analysis only considered the potential impacts of the flooding within Miami-Dade County, New York City, and the District of Columbia, respectively, and the analysis does not take into account population growth, migration, or mitigation efforts.

To determine the percentage of lots developed in southern Miami-Dade County since Hurricane Andrew, NPR used parcel data hosted by the Florida Geographic Data Library and created by the University of Florida GeoPlan Center. To visualize the rapid development, the parcel data was joined to building footprints data created by Microsoft.

The NYCHA developments data was downloaded from NYC Open Data.

The base maps for the other regions also include the building footprints data from Microsoft, as well as road and water data from OpenStreetMap.