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Rising Seas, Imperiled Cities

By Corydon Ireland

A storm surge model of Boston depicts land use impact of a typical high tide (above) and a worst-case scenario storm surge of 5.5 meters (below). Each dot accounts for 100,000 square feet of either residential (yellow), commercial (red), or industrial (purple) built structure.

Around the world, oceans are warming and expanding. Vast ice sheets are crumbling and melting into the sea. The result is global sea-level rise, which will be one of the most dramatic and destructive consequences of climate change.

Of particular concern to human civilization is the fate of the world’s coastal cities. Conservative estimates of sea level rise by the Intergovernmental Panel on Climate Changes (IPCC) project increases of more than half a foot to two feet by the year 2100. More up-to-date analyses by the Arctic Monitoring and Assessment Program, which account for the effects of melting ice sheets around the globe, suggest that sea level will rise three feet to as much as five feet or more by 2100. Ninety years from now, in other words, vast densely populated coastal areas around the world will be underwater, including major cities—unless they prepare. 

Cities at Risk

Getting ready for sea-level rise is every city’s problem. Without action, in fact, rising seas will sooner or later alter most of civilization’s urban footprint. Coastal floodplains worldwide are crowded with cities often built no more than 3 feet above sea level. More than 2 billion people—an estimated 37 percent of the world’s population—live within 60 miles of the coast and would be affected, directly or indirectly, by incursions of the sea.

In sheer economic terms, the stakes of sea-level rise in urban areas are particularly high. An added 0.5 meters (20 inches) of ocean water by the year 2050 would put $28 trillion in assets at risk in the world’s 136 port megacities, according to a 2009 report of scientists and insurance experts assembled by World Wide Fund/Allianz, a global investment and insurance company. On the Northeastern coast of the United States, the expected maximum rise in sea level of 26 inches by 2050 would threaten in five cities alone—Baltimore, Boston, New York, Philadelphia, and Providence—assets worth about $7.4 trillion. In Boston, losses could reach $460 billion, or the equivalent of 20 Big Digs. 

To understand what is at risk, one cannot just look at the current coastline; it’s the highest tide during a storm surge that you worry about.  In Boston, storm surges can temporarily raise sea levels as much as 8 feet, depending on tides, wave action, and the duration and speed of winds. History testifies to the city’s vulnerability: in 1978, Boston’s then brand new Charles River dam was barely in place when a three-day blizzard struck on Feb. 5. The resulting storm tide rise came within 0.4 meters (16 inches) of overtopping the dam. (The Charles River dam was designed to protect against a storm surge of 3.8 meters — about 12 and a half feet — above mean sea level.) What is more, said Wilson in his thesis, the dramatic floods of March and April 2010, which inundated parts of Rhode Island, could also have been catastrophic. Boston’s salvation was the Charles River dam’s six 2,700-hp diesel pumps, which ran 24 hours a day for several days.

Doing something Dutch

Nations and municipalities worldwide have nevertheless been slow to grapple with the implications of sea level rise. The Netherlands, of course, is a conspicuous exception. For centuries, it has struggled with and addressed the fact that much of its territory is below sea level. Between 1950 and 1997, the low-lying nation constructed vast delta works: 250 miles of dams and other barriers.

The city of Venice, Italy, is acting fast, too, because rising seas from the Adriatic are increasingly pushing past the 15th-century city’s three barrier islands. Its system of floating barriers, which will be completed next year after a quarter century of work, is designed to stop storm surges of up to 10 feet from overwhelming the lagoon where Venice is situated.

Two decades ago, London also stepped up to address the problem. Its Thames Barrier, a 570-yard-wide floating span of rotating gates, permits navigation on the river while protecting the city against storm surges and destructive high tides.

But the Dutch remain the world’s gold standard for response to sea-level rise, and are even ready to export their expertise as the world slowly awakens to the problem. Once a nation of dikes and berms, the Netherlands now employs integrated, flexible strategies to keep water at bay. In 2007, a new Delta Committee— the second in five decades—recommended raising the flood protection levels of coastal dikes by a factor of 10. That strengthens an ethos of engineering-first solutions that deepened in the 1960s following a 1953 storm surge breach that killed 1,800 people and flooded the country’s southwest coast.

The same committee advocates two new strategies that rely on sustainability principles instead of engineering. “Building with nature” uses beach nourishment as well as restored natural estuaries and tides to prevent flooding. More radically, a “room for the river” proposal calls for rewriting land use strategies, in part by saving more land along the Rhine and Meuse rivers from development. Implementing these changes will require complex new administrative, legal, and financial frameworks. Such initiatives will also require big money—as much as 3.1 billion Euros ($4.5 billion) every year until 2050.  That’s about 0.5 percent of the country’s current gross domestic product (GDP).

On the other hand, the cost of doing nothing is high, too. A single dike failure could cost the Netherlands up to 50 billion Euros, according to a 2008 study—trillions of Euros if there were multiple failures. Likewise, in New York City, according to the 2009 Allianz report, a single catastrophic hurricane would cost $1 trillion today and $5 trillion by mid-century, when sea-level rise will intensify a big storm’s impact.

Yet most of the world’s cities bordering these rising seas are acting slowly, if at all.

Timely Action

Most city-scale responses have involved “a lot of talk, a lot of thinking, a lot of postponing,” says Jerold S. Kayden, Williams Professor of Urban Planning and Design at the Graduate School of Design (GSD). One problem is uncertainty about the impacts, he says. “It’s a very tricky thing. It’s not happening tomorrow, it’s not happening next year, and it’s not happening in two years.”

Kayden is project director and principal investigator of the Harvard-Netherlands Project on Climate Change, Water, Land Development and Adaption—a project whose partners include Dutch officials. His involvement has already led to two GSD studio workshops; a third is planned for as early as the fall.

Kayden notes that the calculus over how many inches or feet, and by when must be coupled with the one certainty of politics: it moves slowly. “When you begin to align political terms of office, expenditures of money, and [questions such as] who wins, who loses, who pays,” he says, “that constellation leads to a lot of thinking, but it doesn’t lead to action.

Problem as Opportunity 

The particular vulnerabilities and possible solutions to the impact of sea level rise on the Boston metropolitan area are the subject of “Shifting Ground,” a Graduate School of Design master’s thesis by Michael Wilson ’07, M. TK’11.  Wilson is the unusual product of interdisciplinary training in science, engineering, policy and design—all at Harvard.  As an undergraduate, Wilson concentrated in Environmental Science and Public Policy.  After taking a seminar with Professors Daniel Schrag and James McCarthy as a junior, Wilson went on to write his prize-winning senior thesis about the Athabasca oil sands in Alberta, Canada.  “It was the clearest and broadest analysis of the science, economics, and politics of the oil sands that I have ever seen,” says Schrag, who served as Wilson’s undergraduate thesis advisor.

After graduating from the College, Wilson began studying landscape architecture at the Graduate School of Design. When the time came to choose a masters thesis topic, Wilson approached Schrag, who suggested that he explore how sea level rise will affect Boston and what might be done about it. Wilson jumped at the opportunity, engaging in addition to Kayden, Professor of Landscape Architecture Charles Waldheim, Chair of the Department of Landscape Architecture at the GSD, as his principal thesis advisor.

The Range of Response

In the past, engineering provided the preferred menu of solutions to the prospect of encroaching seas: dams, dikes, and seawalls. But as Wilson’s thesis documents, today’s answers to sea-level rise will also involve soft engineering solutions such as wetland restoration.  They may even include measured human retreat from coastlines, allowing rising seas to have their way.

“We would want a portfolio of responses,” says Waldheim, who notes that the Dutch are rediscovering the compatibility of hard and soft solutions. Americans should embrace that combination, too, he says. “Green infrastructure alone [will] not be sufficient. We need a mix.” Green systems can nevertheless build resilience into the framework of responses to sea-level rise. “Fifty-one weeks out of the year or nine years out of the decade, they can look like recreational space.”

Sea-level rise is commonly seen as a problem solely for engineers, but at the same time, notes Waldheim, cities have from the beginning been the sum of “a range of professional inputs,” from engineering and law to design and the arts.

That’s opportune because urban environments are complex places layered with costs that can be measured in multiple ways: economic, cultural, historical, and social. “How to respond,” to sea level rise, says Waldheim, “is an open question.

Wilson suggests a blend of hard and soft engineering solutions  for Boston. A key problem is aging protections for the Charles River basin. Boston is safeguarded to 3.5 meters (about 11 feet) by the New Charles River Dam, completed in 1978. But once intruding water rises beyond 4 meters or so, “Boston is kind of in tough shape,” says Wilson. “It starts to look like the Harbor Islands, except there is a city there.”

In his thesis, Wilson outlines many flood scenarios. One posits a sea-level rise of 2 meters (6.6 feet) in combination with a 100-year storm that produces a surge 5.5 meters (18 feet) above mean sea level. The result would temporarily reduce Boston, including Bunker Hill, to a series of drumlins.

Even a modest rise in sea level—the 12 inches expected by 2046 or sooner, for instance—combined with a powerful storm, a high tide, and the right winds, would make most of Boston briefly part of the Atlantic Ocean. Flooding from storm surges would be accelerated by modern conduits like sewers, subway tunnels, and turnpikes, and by square miles of impervious surfaces that don’t soak up water but instead channel it into the heart of the city’s infrastructure.

So even with a modest projection in sea-level rise, waves from an Atlantic storm could send ocean water cascading into the subway stops at South Station or Aquarium, for example. Landmarks such as Faneuil Hall would be partially submerged. Wilson has modeled the “potential inundation areas and impacts,” of flooding across a range from 1.5 meters (5 feet) to 5.5 meters (18 feet) above mean sea level. The results likely “over-represent” flooded areas, he says, but it’s a start. “You need a holistic, messy picture.” The real point is to begin demonstrating the “pressure on the system” exerted by storm surges in a world of higher sea levels, and to test how existing protections work—or fail.

The engineering ethos that shaped Boston—much of which is built on landfill—survives in what has become an iconic proposal for protecting the city from the sea: local architect Antonio Di Mambro’s 1988 proposal for a Boston Harbor Barrier that would stretch from Quincy to Winthrop, and include a tidal surge barrier, new transit pathways, and commercial and residential development.

While acknowledging the boldness of Di Mambro’s vision, Wilson proposes a smaller-scale engineering solution to protect the city. His work explicity points out that fort-like protection structures and other brick-and-mortar projects no longer provide all the answers. Kayden agrees: “We’ve moved away from confidence in engineering solutions [alone]. We’ve widened the lens dramatically about what we can conceive is possible.”

A re-imagined Boston Harbor would have improved seawalls, yes—but Wilson suggests it would also include “climate parks,” retention areas, and parkways that recapture the nineteenth century vision of an “emerald necklace” around Boston. His solution harks back in part to a Boston landscape of an earlier era, marked by marshes and mudflats. Wilson envisions “renewing” the last half-mile of the Charles River by creating a wetland that extends the saltwater/freshwater interface, along with a terraced berm on the waterfront. And his reconception of Paul Revere Park, a five acre open space located where the Charles River meets the inner harbor, would introduce a tidal mudflat and marsh bisected by pedestrian bridges.

Wilson also proposes “leveraging” highway infrastructure—some of it abandoned, failed, or underutilized—for flood control. A system of urban retention areas for flood waters would use everything from Back Bay back alleyways to the partially closed Rutherford Avenue underpass, which would be abandoned as a road and seeded with water-tolerant plants. Such a “retention strategy” could even be regional, says Wilson, by including a network of coastal wetlands along the upland portions of the Charles River. Although Wilson’s work focused primarily on Boston proper, it also touched on sea-level impacts to Cambridge, Somerville, Medford, Malden, and Winchester—and from Revere and Winthrop as far south as Quincy. Regionalizing the response to sea-level rise makes sense because storm surge impacts—perhaps counter-intuitively—will have greater impact inland than in Boston Harbor itself, explains Wilson, citing a 2007 model of impacts developed by the Federal Emergency Management Agency. 

Wilson pairs these soft engineering solutions with a hard and expensive one: a massive swing-out storm surge barrier like the one that protects Europoort and the port of Rotterdam 17 miles inland. (The Europoort barrier cost the Dutch $3 billion two decades ago.) When deployed, two steel triangles as high as skyscrapers would pivot on “the world’s largest ball and socket joints,”  explains Wilson, as they swing out into the channel between Castle Island in South Boston and Logan Airport in East Boston. Pontoons would fill with water, the barrier would sink, and then lock into a submerged concrete pad. “It’s a big, big, big piece of infrastructure,” he says—but would protect Boston to a mean sea level rise of 5.5 meters (18 feet). It would also augment existing safeguards on the Charles and Mystic rivers by adding 2 meters (6.6 feet) of protection. “The nice thing is, it more or less fits in the existing channel of Boston Harbor,” says Wilson. “If we built it once in Rotterdam, we can build it again in Boston. The engineering challenges are solvable.” 

Other challenges will follow, he predicts, including objections based on sentiment. For one, “You would be building something the size of the Eiffel Tower next to a historic monument.” Castle Island, continuously occupied longer than any other fortification in British North America, is on the National Register of Historic Places, along with Fort Independence. Complementing this historic landscape are a picnic area, a ballpark, and a popular pond called Pleasure Bay. These recreational amenities enjoyed by generations of Bostonians would suddenly be dominated by a giant steel barrier.

The time to act is now, says Wilson, especially since any solution to sea-level rise will take at least a generation to plan and build. He offers an example: in 1955, Hurricane Diane—the wettest tropical cyclone in the history of the Northeast and the first billion-dollar storm to strike the U.S.—flooded New England. That prompted the construction of the New Charles River Dam…23 years later. The interim between the disastrous flood and the solution was taken up with planning, analysis, stakeholder hearings, and reports from consultants. “The time to be thinking about what we want to do in 20 years or in 40, is now.” Where do we want to be, he asks? What is required? What institutions need to be in place? And who will pay?

A Rising-Seas Seminar

The questions raised by Wilson’s study of sea-level rise in Boston have encouraged new dialogues about law, policy, political action, and regional collaboration.  These discussions will bear fruit next spring when  Harvard experts in law, climate change, engineering, landscape design, and urban planning convene a graduate seminar to address the complex problems associated with how cities will adapt to sea-level rise. The course will look at case studies worldwide, drawing on generations of expertise gathered by the Dutch as well as the less hopeful case of Dacca, Bangladesh, where a city of 15 million sits at sea level in a broad and flat river delta. Because of its lack of protective infrastructure, as well as the risk of sudden mass migrations inland, Dacca is a case of extreme vulnerability. Waldheim calls it “a test case of another category.”

The course will focus principally on Boston, as an estuarial city with a three-century history of design and engineering projects that engage the ever-present sea. “It’s a city that has been well-designed and -studied,” says Waldheim.

Harvard Law School professor David Barron, one of the course organizers, has for the past five years co-taught a “green cities” seminar with Brandeis Professor of Law Gerald Frug and guest lecturers from the New York City Law Department. The two-semester offering, a fall seminar and a spring practicum, investigates how cities organize themselves to address climate change and how they use sustainability as an economic development strategy.

But Barron’s seminar awoke to sea-level rise—“as important a public problem for cities as exists,” he says—only recently, after a guest lecture by structural engineer and architect Guy Nordenson, who teaches at Princeton and practices in New York. Last year, Nordenson participated in a project that re-envisioned New York City’s harbor and coastline in the face of climate change. The visionary adaptations he presented, drawn from “Rising Currents: Projects for New York’s Waterfront,” an exhibition and lecture series at the Museum of Modern Art and at MoMA PS1, prompted Harvard law students to ponder the governance challenges and legal implications of sea-level rise along urbanized ocean shores.

Rising seas will trigger problems that go well beyond ecology and engineering, especially on intricately organized, urbanized coastlines that are ill prepared for widespread inundation. Government, public authorities, regulators, and businesses are not used to large–scale cooperation. But somehow, in a matter of years or decades at the most, they will have to collectively address a thicket of legal, social, economic, and even moral issues around the subject of rising sea levels. Issues of ownership and equity in protections will be tricky. “The question of legal authority over the relevant territory is incredibly complicated,” says Barron.

One example of that complexity is the fragmented network of seawalls in the Boston region—many of them privately owned—mapped in Wilson’s master’s thesis. “You would have to fill a lot of seawall over a lot of private land,” says Wilson (who now lives in New York, where he works for landscape architecture firm Michael Van Valkenburgh Associates) The complex technical, scientific, social, legal, and regulatory challenges “multiply from there,” he says, so using “a localized case study will sharpen the practical issues.” The course designers, including Barron, Frug, Kayden, Schrag, and Waldheim, say it might even provide a template for study and action worldwide.

In a warmup to the spring course, Kayden plans a workshop at the GSD to investigate what Boston needs to do to get ready for sea-level rise. He describes it as “a day-long thinking-through” that will include experts from two water-related ministries in the Netherlands along with officials from the City of Boston. “Like any city, Boston is confronting a range of adaptive strategies, from hard engineering to land controls to building design adaption,” Kayden explains. “There is no deeply accepted one-size-fits-all approach, nor is there a broad political consensus yet. It hasn’t ripened to that point. There are conversations, there is thinking in the City, and thinking at Harvard.”

A few American cities are in what Kayden calls “the conversation and study stage.” In Boston last November, a daylong forum sponsored by the Boston Harbor Association considered potential impacts. Talk turned to flood-proofed buildings and retention ponds—and even to a massive sea barrier that would protect the inner harbor. Ellen Douglas of UMass Boston and former Tufts professor Paul Kirshen—now with the Battelle Institute—mapped out future scenarios in which Boston is hit by record storm surges. By mid-century, the city can expect the equivalent of today’s 100-year storm every two to four years; by 2100 the city can expect a “100-year” storm every year. San Francisco and New York have sponsored similar public forums on the issue.

One of the crucial questions cities will have to answer is, “Should I put my money into protection or should I put my money into relocation?” says Schrag. “Retreat has to at least remain on the table,” he points out, “because investment in engineering solutions will help, but only for a period of time. After the first half meter of sea level rise comes the next. Glaciers are going to keep melting, ice sheets are going to keep melting.”

The idea of retreat from coastal cities, as happened in New Orleans after Katrina—with all its horror, drama, and expense—is an extreme example of what lies ahead,  says Waldheim, and a vivid inducement to cities to study, converse, imagine—and act soon.


This article is adapted from Environment@Harvard Volume 3, Issue 2.