Sea level rise threatens New Bedford’s fishing port and could put South Coast towns under water, new report finds

The Hurricane gate in New Bedford Harbor was closed during Tropical Storm Henri lashed the South Coast last year.John Tlumacki/Globe Staff

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Rising seas along the South Coast are projected to have catastrophic effects, inundating towns around Buzzards Bay and Narraganset Bay, flooding out roads, and wiping away salt marshes that store vast amounts of carbon, according to a new report.

The report, issued by the conservation group Trustees of Reservations, details how more than two feet of projected sea level rise by 2050 would affect communities along Massachusetts’ South Coast, offering a grim view for planners as they look to shore up the most vulnerable parts of their towns and cities. In some case, it gives reason to consider retreating from the shoreline.

“These low-lying communities, especially in areas along the coast, are potentially going to start seeing sea water impacting low-lying roads and these areas on a daily basis, or multiple times a year,” said Brittany Hoffnagle, a climate resiliency specialist at the Woods Hole Group, a Bourne-based international environmental services company, who led the analysis in the report.

The projections in the report are based on a worst-case, high-emissions scenario in which the world fails to halt emissions from fossil fuels. The state recommends that planners use that scenario in plotting future growth in their communities, said Hoffnagle.

To produce the report, the Trustees and the Woods Hole Group took publicly available state and federal data on future flooding, saltwater marsh risks, and erosion and overlaid it with community data on where buildings and roads are.

The report covers the coastline from Seekonk to Falmouth, zeroing in on the 14 towns that border Buzzards Bay and Narragansett Bay. While the seas there have risen roughly 9 inches in the last 75 years, that’s minuscule compared to the 2.6 feet of rise that could occur by mid-century.

Projected flooding on the South Coast

On the map below from The Trustees of Reservations, click the arrow to see projected flooding in 2030, 2050, and 2070.

Some communities in the area they studied are more vulnerable than others, said Cynthia Dittbrenner, director of Coast and Natural Resources at the Trustees of Reservations.

“Because of the orientation of Buzzards Bay — kind of south facing — when storms come in, that water comes into the bay and it creates a funnel effect that has more impact on the northernmost towns because the water is concentrating to those areas,” Dittbrenner said.

The worst effects are expected in Bourne, Marion, Mattapoisett, and especially Wareham.

According to the report, Wareham, a town of roughly 22,000 people that sits at the heart of Buzzards Bay, would see dramatic impacts not just during a storm, but during daily high tides. Twice a day, when the tide hits its peak, 250 buildings in the town could be inundated. A 10-year flood could impact 4,326 buildings — more than a quarter of those in town— and put 61 miles of road under water.

Kenneth Buckland, Wareham’s director of planning and community development, said the report highlights the intensity of the problem, “making it more real as to the number of people that are affected by the enormity of the issue.”

In Wareham, they’re left with tough choices. “Where people can afford it, we need to look at retreat and moving properties, relocating people out of the floodplain,” said Buckland. Those decisions, he said, will largely be left to individual homeowners and their bankers, and whether they can justify further investment “before the sea starts lapping at their doorstep,” he said.

But there are environmental justice neighborhoods in the floodplain, too, with people who can’t afford to up and move. “We’ll have to find locations where housing density can be increased and site them in there if they want to move,” he said.

In New Bedford, home to the nation’s most valuable fishing port, a hurricane barrier that has long protected the area from high seas could introduce new challenges.

The New Bedford barrier has been protecting the Port of New Bedford from hurricanes since it opened in 1966. When a storm or king tide threatens dangerous sea levels, officials can close the gate and maintain the water level and protect the coastline. Already, it’s closing more and more as sea levels rise because of climate change, and when the gates are closed, fishing boats can’t get in or out.

By 2050, the barrier could be closed between one and two times a day as tides push the water levels higher than the current threshold, according to the report.

“You can’t have a working waterfront like that,” said Michele Paul, director of resilience and environmental stewardship for New Bedford. “We’re going to have to, at some point, decide that we’re keeping the gates open unless there’s an actual hurricane.”

That means the docks and industrial buildings will need to be made ready for higher seas, and that New Bedford’s neighbors in Fairhaven, where homes are built along the shore, may have to consider relocation.

Beyond the impacts to towns and cities, the report also projects a dire future for the coastal environment. Roughly one third of the 250 miles of shoreline that make up Buzzards Bay and Narragansett Bay are salt marsh, and they are especially at risk from sea level rise, according to the report.

Salt marshes are among the most productive ecosystems on the planet. They also play a crucial role in protecting the planet by soaking up and sequestering massive amounts of carbon — more than 10 times the amount that forests sequester.

But the marshes along the South Coast risk being inundated by 2050 —some 20 years sooner than marshes in other parts of the state, according to Dittbrenner. “We need to be going in and making sure we’re restoring those marshes to give them a fighting chance against sea level rise,” she said. “And we also need to be looking at the areas adjacent to marshes that are slightly upland where we think marshes could migrate to, and protecting and preparing those areas.”

Looking ahead, Dittbrenner hopes that towns will use this report to help with their planning work in tandem with resilience work they are doing with the state. “We don’t want this to just be a report that sits on a shelf and then nothing ever happens with it,” she said. “We want it to be able to help the communities and help increase resilience work in the area.”

Clarification: This story has been updated to reflect that the report focuses on the South Coast.

Dharna Noor of the Globe staff contributed to this report.