SCOTT SIMON, HOST:
Philadelphia is filled with history central to the founding of the United States. It's where the Declaration of Independence was signed. It's where the Constitution was drafted. Sophia Schmidt of member station WHYY has this report on how landmarks there are being threatened by human driven climate change.
SOPHIA SCHMIDT, BYLINE: Fort Mifflin sits on the banks of the Delaware River. It's surrounded by a thick wall.
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SCHMIDT: Beth Beatty leads the nonprofit that takes care of the site. She shows me around the yellow brick buildings, as planes from the nearby airport fly overhead.
And what's this water we're crossing?
BETH BEATTY: This is - the fort is surrounded by a moat.
SCHMIDT: A welcome sign reads, the fort that saved America. That's because patriot forces at the fort delayed British supply ships from getting north during the war. Beatty says that gave George Washington and his troops time to flee to Valley Forge, northwest of Philadelphia.
BEATTY: Fort Mifflin was instrumental in forcing the war to go on, and allowing Washington the time that he needed to achieve his victory.
SCHMIDT: The fort's riverfront location was a strength during the Revolutionary War. But today, it's a liability. Beatty says water often pools on the grounds when it rains, and an old, faulty tide gate lets river water into the moat. In January, an intense rainstorm, coupled with a high tide and extreme winds, brought the river to a record level. That pushed water over the sea wall that surrounds the fort. Beatty found the evidence after the water receded.
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BEATTY: So you can see there is debris up here, indicative of the water coming over the top of the moat.
SCHMIDT: The wind peeled part of a reproduction metal roof off the officer's quarters. The grassy area inside the fort wall flooded along with a renovated historic hospital building on the grounds.
BEATTY: But here we are.
SCHMIDT: Beatty shows me the first floor of the hospital building, where staff cleaned up a thin film of mud the water left behind.
BEATTY: The problem was in our back room, which is storage, including storage of fabric, storage of cast iron, storage of historic clothing, but, you know, reproduction for our staff to wear. So...
SCHMIDT: Back when the fort was built in the 1700s, the area was called Mud Island, so it's always been a little soggy. But human-caused climate change is making the problem worse. The Delaware River is rising, already more than a foot since 1900. William Sweet is an oceanographer with the National Oceanic and Atmospheric Administration. He says this trend is accelerating because of climate change.
WILLIAM SWEET: When we look over the next 30 years or out to 2050, let's say, since 2020, the amount of sea level rise that we're expecting in the Philadelphia region is approaching a foot.
SCHMIDT: That means higher high tides and more frequent floods. Sweet says by 2050, it's possible the fort could flood, on average, five times a year. Beatty worries over time the rising river and heavier rains will compromise the foundations of the old buildings. And it's not just Fort Mifflin. Historic preservation advocates say the threat from climate-linked disasters across the country will continue to grow.
JIM LINDBERG: This is an issue that is increasingly apparent.
SCHMIDT: Jim Lindberg is the policy director at the National Trust for Historic Preservation, which tracks historic places in danger of disappearing. He says Fort Mifflin is like a lot of historic military structures along coasts and waterways.
LINDBERG: You know, it's not easy to protect these places because they are, in some cases, literally with their feet in the water, so to speak.
SCHMIDT: Climate-fueled disasters like wildfires and hurricanes have damaged historic sites across the country, including a ranch outside of Los Angeles used for Hollywood sets and the first Black cemetery in Houston. Lindberg says in some places, adapting to climate change may mean letting the water win.
LINDBERG: It may mean pulling back, letting certain things go. This is, I think, going to have to be part of the conversation.
SCHMIDT: Beth Beatty at Fort Mifflin doesn't want to let go. She wants to modernize the fort's century-old tide gate and look into other possible solutions, like dredging the moat. Beatty expects it would be expensive. But she says the fort's future depends on adapting to climate change.
For NPR News, I'm Sophia Schmidt in Philadelphia.
(SOUNDBITE OF BREMER/MCCOY'S "PA VEJ") Transcript provided by NPR, Copyright NPR.
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