The Boston Harbor Association

Today's 100-year storm surge could be tomorrow's high tide.

Coastal cities are now living in what Brian Swett calls a “post-Sandy environment.” In this new reality, there is no more denying the specter of sea-level rise or punting on plans to prepare for it. And there is no more need to talk of climate change in abstract predictions and science-speak. We now know exactly what it could look like.

In this environment, The Boston Harbor Association is somewhat fortuitously releasing today a major scientific report, long in the works, on what coming sea-level rise could mean for the city. And if Sandy had any silver living, says Swett, Boston’s Environment and Energy Chief, it is that residents are now as ready as ever to listen.

"I have yet to see a scientific report on sea level rise or storm surge that makes me less concerned," Swett says of his own reaction to the dramatic picture portrayed in the new report, Preparing for the Rising Tide. "It seems like the more we know, the more onus and important pressure there is on taking action."

The report’s authors modeled two scenarios for the city: one in which flood levels rise to 5 feet above the average high tide today, and one in which flood waters rise 7½ feet above current high tide. The first scenario corresponds to the equivalent of a 100-year storm surge today (meaning the kind of storm that has a 1 percent likelihood of happening this year). This map from the report illustrates exactly what this would look like in the city:

"Preparing for the Rising Tide"

To put the picture in even more relatable terms, that map also shows what would have happened had Sandy’s storm surge reached Boston 5½ hours earlier than it did, striking at high tide. Had that happened, 6.6 percent of the city could have been flooded, right up to the steps of City Hall. If average sea levels rise by 5 feet – a possibility by the year 2100 – today’s 100-year flood pictured above would become the city’s new normal, occurring twice a day at high tide. At that sea level, a moderate storm surge of another few feet could inundate 30 percent of the city.

This second map shows flood depths up to 7.5 feet, a scenario that represents what a 100-year storm surge might look like come 2050:

"Preparing for the Rising Tide"

Paul Kirshen, one of scientists who authored the report, is conscious of the fact that these maps will strike a chord with people in Boston today in a way they might not have before Sandy’s landfall last October. "As scientists, we feel that the public should be receptive all the time to this sort of stuff," he says dryly. "But that’s not the reality."

Now Boston must begin to contend with the reality that it could be even more vulnerable than New York to rising sea levels. Much of Boston was historically built on land filled in and created out of estuaries and wetlands, and the ocean itself. Logan International Airport was built on man-made land. So were many of the high-end residences in the city’s Back Bay neighborhood.

"It’s interesting when we actually look at the maps," says Vivien Li, the president of The Boston Harbor Association. "Where it would be flooded is where we filled in."

This historic map of Boston, from 1640, shows a peninsular city with a dramatically different shape, inside the outlines of Boston as we know it today (as Boston College professor Jeffrey Howe writes, the ensuing sequence of landfill projects "also helps explain some of the peculiarities of the modern urban landscape. Boston streets, laid out in the 17th and 18th century, followed a coastline which has moved and avoided hills which are no longer there.")

Jeffrey Howe

On an individual building-by-building basis, the report suggests that every property in those flood zones will need to begin to think about adaptations today. The scale of such an undertaking seems overwhelming, but local businesses that have previewed the report no longer sound as if they're shirking the challenge. "None of them are saying 'oh this is never going to happen, forget it, you environmentalists are just overreacting,'" Li says. "But rather ‘how much time do we have?'"

The answer, according to scientist Ellen Douglas, who also worked on the report, is that the city is quickly running out of time – especially given that it will take years to prepare. “We can’t just decide to adapt the city next year," she says. But the report attempts to argue that changes today are doable (the report includes two case study assessments of buildings on particularly susceptible ground).

Going forward, new development – and much of it is planned on Boston’s waterfront – will need to adapt at the planning stages. In conjunction with the report, Mayor Thomas Menino’s office released today a series of proposals for the next iteration of the city’s Climate Action Plan, due out in 2014. The city government plans in the next six months to include climate change preparedness as a required design component in the city’s development review guidelines, and to model new guidelines for better enforcing flood-proofing standards on existing buildings.

In a city so historically connected to water, it will be impossible to relocate people and buildings out of its way as tides creep further inland. Traditionally, coastal communities have tried to protect themselves with berms and sea walls. But those tactics alone won’t keep all of Boston dry in the future. And so the report also proposes another option: that the city may need to learn to live with flooding."

"That’s not been the approach historically in the West or in Europe," Kirshen says. "But now with sea-level rise – and the fact that it can’t be stopped – we’re realizing that we may have to let some areas flood. We may have live with water."

That could mean creating or preserving open space for floodplains, or re-envisioning the ground-floor uses of existing buildings. First floors could be converted to uses that would withstand a passing flood, like parking lots. And crucial building utilities could be relocated out of basements to higher floors. These are the types of changes that building owners need to start thinking about today.

"This is an area where we’re never going to check the box and say we’re fully prepared for climate change and sea-level rise," Swett says. But the idea is to try to continuously adapt.

Today’s report addresses only one element of what the city must focus on in the coming years, its most susceptible buildings. Boston’s basic infrastructure – its sewer, transit and road arteries – will pose entirely different challenges. And as New York learned during Sandy, it does little good to have a flood-proofed building if the city’s underlying infrastructure is vulnerable (or, for that matter, to have functioning power and sewer infrastructure if your building lobby is flooded). Boston, and other coastal cities like it, will have to work on those two pieces of adaptation in concert, all while keeping in mind one other piece of the climate picture.

"Mitigation remains incredibly important,” Douglas says. "Mitigation means the difference between 2 feet of sea-level rise and 6 feet of sea-level rise. Just because we’re focusing on adaption doesn’t mean we’re giving up on mitigation."

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