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Rising seas pose an existential threat to the Massachusetts Bay Transportation Authority’s rail network over the next 50 years, carrying the potential to inundate vast portions of the system and sever crucial links that shuttle hundreds of thousands of riders across the region each day, a new study has found.

The report, written by researchers from the Massachusetts Institute of Technology and Tulane University, warns that the system must take sweeping action to fortify its coastal infrastructure against the realities of a warming planet.

“Severe flooding is a grave challenge for the T,” said Michael Martello, a researcher in MIT’s Transit Lab and lead author of the report, which was commissioned by the MBTA.

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The study is slated for publication next month in the journal Transportation Research and used sea level rise projections to determine what segments of the system’s four major subway lines might be rendered inoperable by floodwaters from a so-called 100-year storm.

Its conclusions were dire. As soon as 2030, a 100-year storm would completely inundate the Blue Line and large portions of the Red and Orange lines, researchers found. By 2070, a 100-year storm would flood nearly the entire network, sparing only some sections of the Green and Orange lines, with “system connectivity” reduced to just 9 percent.

“It’s not a pretty picture,” says Jesse Keenan, a Tulane University professor who studies the intersection of climate change and infrastructure and co-authored the research. Keenan said the surreal scenes from the massive rainstorm in early January of 2018, which sent floodwaters pouring into the Blue Line’s Aquarium Station and shut down service between Wonderland and Orient Heights, will become far more common.

“The probability of a one in 100 year event is now at one in 50 or one in 40,” he said. “It’s just going to happen a lot more frequently.”

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Hannah Lyons-Galante, the MBTA’s climate change resiliency specialist, said the findings were “informative, but not surprising, given the susceptibility of all of Boston to sea level rise and storm surge.”

She said the MBTA is working with climate resiliency groups and Boston officials on long-term plans to protect the transit network from rising seas.

Waters around Boston have risen about 8 inches over the past 70 years, a little more than an inch every decade, according to data from the National Oceanic and Atmospheric Administration. But seas are rising much faster now. By the 2030s, the sea level around Boston is expected to climb 9 inches above levels recorded in 2000, even if there is a major reduction in carbon emissions, the city’s environment department projects.

On their own, those predictions are alarming. Coupled with the expectation that coastal storms will become more frequent and severe, the threat to the MBTA becomes “existential,” researchers said.

“The recovery challenges of such a scenario, would be immense, complex, and call into question the possibility of service restoration,” the study said of a severe coastal storm in 2070.

For some cities, the theoretical has become very real. A dozen people died on a deluged subway train last week in Zhengzhou, China, after days of torrential rain, and parts of the New York City subway system filled with water during a storm earlier this month.

In Boston, the MBTA’s Blue Line ranked as the most susceptible to floods, the report found. The system’s lowest-lying rapid train line, it was first constructed in 1904 on man-made land that is “essentially right at sea level,” Martello said.

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A severe coastal storm this year might render the entire line inoperable, mainly due to flooding in the tunnels under Boston Harbor and over railways in East Boston, the study found.

The Blue Line is a vital connection to East Boston and Revere, which are cut off from downtown by Boston Harbor, and provides transportation to more low-income people than the three other major lines, according to MBTA data.

“The MBTA is a lifeline for transit-dependent riders and people from environmental justice communities like East Boston,” said Staci Rubin, vice president of environmental justice at the Conservation Law Foundation. “We’re talking about a crisis situation.”

“A shutdown in service means that people can’t get to work,” she said. “It means that people are not able to get to medical appointments that are critical. It can also mean being late to pick up your child from day care.”

In response to the threat, the MBTA has directed nearly $2 million to a number of short-term projects they hope will prevent flooding on the Blue Line.

Deployable flood doors have been installed at the Aquarium stop and workers last summer waterproofed cracks and repaired worn concrete in the tunnel under Boston Harbor.

“It’s very good for these major events — the kind that we saw in 2018,” Lyons-Galante said. “It keeps major amounts of water from coming down into our stations.”

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But specialists say the scope of the problem demands more systemic solutions.

“The near-term steps are dwarfed by the need for a substantive and critical systemwide investment that can help protect the system from the impacts associated with climate,” said Rick Dimino, Boston’s former transportation commissioner and the president of A Better City, a business group that focuses on transportation and infrastructure issues.

Such an undertaking will likely require significant state funding, as MBTA officials say they cannot presently afford to make changes of such magnitude.

“We have such a challenge to just run safe, reliable service and tackle our own immediate needs that it’s very difficult for us to divide our attention, or our resources, and try to put (them) toward what is really a landscape-scale effort to prevent flooding in the whole region,” Lyons-Galante said.

Climate specialists and public transit advocates say the urgency of the issue requires swift action.

“It’s about the economic vitality of the city,” Keenan said. “If you do not do this, you’re going to lose businesses and jobs, you’re going to lose tenants, you’re going to lose taxpayers, you’re going to lose economic activity. People need to get to work.”


Andrew Brinker can be reached at andrew.brinker@globe.com. Follow him on Twitter at @andrewnbrinker.