On a chilly Sunday afternoon in the spring of 2016, a group of designers and preservation professionals wandered through one of Newport, Rhode Island’s oldest neighborhoods, visualizing what it would look like underwater. It wasn’t hard to imagine water flowing down the narrow streets and into the basements of the quaint, colonial-era homes located just blocks from Newport Harbor and a mere four feet above sea level. Some had already seen it.

In 2012, Hurricane Sandy sent floodwaters into many of the Point neighborhood’s historic homes, including 74 Bridge Street, a red-painted, two-story house originally built in the late 1720s. The basement flooded up to the first-floor framing and the kitchen took on at least seven inches of water.

Two years later, the Newport Restoration Foundation (NRF), a nonprofit preservation group founded by Doris Duke in the 1960s, purchased the house at 74 Bridge Street. As the house of one of Newport’s most notable cabinetmakers, a Quaker named Christopher Townsend, it had sat for years at the top of the NRF’s list of most desirable historic Newport properties. It was an important acquisition for the NRF, which currently owns 78 properties throughout the city and helps fund their upkeep. But the organization also knew that 74 Bridge Street would flood again.

“It’s in the lowest point in the Point neighborhood—literally, the lowest topographical point,” says Shantia Anderheggen, NRF’s former director of preservation. With sea levels on the rise—and in Newport they already had risen 11 inches over the past century—it was a statistical certainty that what happened in 2012 would happen again. And it wasn’t just the Townsend residence. The entire Point neighborhood, which has one of the highest concentrations of colonial-era structures on the continent, was under siege from the sea.

Since the passage of the National Historic Preservation Act in 1966, preservation decisions have tended to be made, out of necessity, case by case in response to specific and often urgent threats. But the regulations that govern historic resources make little provision for a changing environment. “Increasingly, we’re going to have to make decisions on such a large scale that our current practice of assessing each case individually is just not going to be practical anymore,” says Anthony Veerkamp, the director of programs for the National Trust for Historic Preservation’s Preservation Green Lab (now the Research & Policy Lab). “We’re going to need more clarity, and that’s likely going to mean more flexibility.”

At the moment, owners of historic properties find themselves caught between conflicting regulations. In response to recent storms and rising sea levels, the Federal Emergency Management Agency (FEMA) has been updating its flood maps. Properties that were not previously in a floodplain are now sometimes well below FEMA’s base flood elevation. To qualify for flood insurance (or a mortgage, which requires flood insurance), the property may need to be elevated. But doing so could threaten the property’s place on the National Register, a distinction that can also make property owners eligible for crucial rehabilitation tax credits. Of course, equally important in a place like the Point is the urban fabric, which could be significantly disrupted by piecemeal resilience efforts.

In 2016, the NRF organized a conference called Keeping History Above Water. It took place over four days at the Newport Marriott two blocks from 74 Bridge Street. More than 400 people representing nearly 20 disciplines attended, some from as far as Iran. At the Townsend property, the NRF mounted an exhibition examining the threats the neighborhood house faced, as well as the problems that adaptation measures might cause. At the heart of the conference was a single question: How do you weigh the need to adapt to the future against the imperative to preserve the past? Or as Teresa Crean, a planner with the University of Rhode Island Coastal Resources Center, put it, “How do you manage those structures with the fact that the floodplain is changing? Do you focus on making sure they’re flood-proof while preserving some aspect of historic integrity? Or do we say historic integrity is more important, they’re going to flood, and that’s just how it is?”

This tension is being felt throughout the preservation world, as sea-level rise, exacerbated by global climate change, threatens to damage and even erase coastal historic resources. In Newport alone, there are 548 buildings that are either listed or eligible to be listed on the National Register of Historic Places that are also in a flood zone, according to the Coastal Resources Center. For many, there is an acute sense that history itself is at stake. An individual building can be fortified or moved, but what about the historic landscape? What about historic downtowns or entire neighborhoods like the Point? It’s one thing to propose that communities retreat from the coast. It’s another to accept that when they do, they won’t be taking their history with them.

For the preservation profession, sea-level rise is a new and confounding problem, one that complicates an already complex decision-making matrix. “We’re used to how water gets into buildings from the sky,” says Anderheggen, who now owns the consulting firm Preservation Strategies. The issue also has brought an army of new disciplines, such as climate science and oceanography, into the mix. “We’re used to dealing with developers, economists, architectural historians,” she says.

Sea-level rise is also a multifaceted threat: There is, yes, the danger that creeping floodwaters bring, but there is also the challenge posed by adaptation measures themselves. To make a building or landscape more resilient often necessitates some degree of change to the historic fabric or landscape character. How much change can a property endure before it no longer retains its historic significance? And should changes brought on by resilience efforts be weighed differently from those proposed for other reasons?

Randall Mason, an associate professor of historic preservation at the University of Pennsylvania School of Design, says his field has undergone a fundamental shift in recent years, in part owing to these types of challenges. “It’s the difference between objects and systems,” Mason explains. “Objects are supposed to stay the way they are, and if they’re broken, you can fix them. Systems are always changing. And landscapes, by their very definition, are always evolving, always changing. So the approach that more progressive historic preservation thinking adopts is about managing change.”

Mason points to his hometown of Atlantic City, New Jersey, as an example. The boardwalk that runs most of the length of the barrier island city has existed in some form or another for the past one and a half centuries. Not a single board remains from the original wood structure, however. By 1890, Atlantic City was already on its fourth iteration of the walkway. Many of the boardwalk’s now iconic elements—for instance, the wood decking’s herringbone pattern—weren’t added until 1916. “It’s been destroyed and rebuilt numerous times, but it always serves the same cultural function,” Mason says.

Of course, there are landmarks, like the Statue of Liberty, that will be preserved at all costs. But in many places, Mason says, “there’s going to have to be a give-and-take between the cultural values and the ecological and economic values.”

Around the country, landscape architects are finding themselves in the midst of, and often guiding, these negotiations. This past November, CMG Landscape Architecture was selected as part of a team to redesign a portion of San Francisco’s Embarcadero, a three-mile-long waterfront district that includes a number of historic piers and wharf buildings, several of which are listed on the National Register of Historic Places. The area is vulnerable not only to rising sea levels but future earthquakes, which threaten to compromise the existing seawall, the foundation of the entire waterfront. If the seawall fails, roads, buildings, transit systems, and other critical infrastructure will almost certainly suffer significant damage.

To prevent such a catastrophe, the Port of San Francisco is undertaking a huge, multiphase re-engineering project, led by the Netherlands-based consultancy Arcadis and CH2M, with CMG in charge of urban design. The team is also in charge of retrofitting the Embarcadero to respond to sea-level rise.

Already, certain areas are inundated during abnormally high tides, known as king tides. The task is to develop a more resilient waterfront that also retains the integrity of its historic fabric. How to do both is the question, says Kevin Conger, FASLA, a founding partner of CMG. “We don’t have the answers,” he says. “There are going to be trade-offs, inevitably.”

How to balance those trade-offs is something property owners and preservation professionals will need help with in coming years. Thus far guidance has been limited. The planning frameworks and design guidelines that do exist are often geared toward private property owners and focus on historic structures, ignoring landscape elements and the cumulative impact of individual adaptations. Of course, a one-size-fits-all approach is at odds with the most basic premises of historic preservation, and to some degree every climate adaptation plan will be unique. But city officials and policy makers are also going to need new tools if they are going to respond to sea-level rise in culturally sensitive ways, Conger says. Three thousand miles away in North Carolina, a researcher named Erin Seekamp thinks one of those tools might just be an algorithm.

Seekamp is an associate professor in the Department of Parks, Recreation, and Tourism Management at North Carolina State University. She is also the creator of the Optimal Preservation Model, or OptiPres, a tool designed to help municipalities and government agencies like the National Park Service (NPS) balance preservation values with the realities of sea-level rise and thinly stretched budgets. Seekamp got the idea for OptiPres after realizing that NPS had a method for assessing a landscape’s vulnerability to sea-level rise but no way to determine how adaptation measures will affect the integrity of its historic and cultural resources.

According to NPS, $40 billion worth of cultural resources and park infrastructure is at risk from sea-level rise. Given that the agency already faces a backlog of deferred maintenance, park managers will have to decide which resources to save and which to let wash away. OptiPres allows for an informed sort of triage. It works by using an optimization algorithm to evaluate the impact of every possible climate adaptation action—including elevation and relocation—on a particular resource’s historic significance. Each scenario is evaluated over a specified planning horizon and budget, and the result is a series of data visualizations that provide the “optimal” approach for each building modeled—in other words, those actions that will provide the most resilience but do the least damage. Seekamp spent two years developing the framework with input from NPS, the U.S. Geological Survey, and state historic preservation offices from around the country, developing quantifiable metrics for a historic resource’s character, condition, and potential use.

In 2017, OptiPres was piloted at Cape Lookout National Seashore in North Carolina, a chain of barrier islands that is home to herds of wild horses as well as two historic villages that are listed on the National Register of Historic Places. The islands are managed by NPS and, according to an assessment conducted by a team at Western Carolina University, are at extreme risk from sea-level rise.

OptiPres was used to analyze 17 historic buildings over a 30-year span. Initially, Seekamp had planned to include every cultural resource within the national seashore’s boundary, but as she and the team developed its framework, assigning values and weights to everything from a resource’s uniqueness to its spatial significance, they kept having to scale it back. “We got to the two historic districts, and then we couldn’t include the landscape elements because it takes so much to build the model,” she says. The districts were too large still, and the team eventually selected a representative sample of buildings within them. Even at that scale, Seekamp says, the model requires a supercomputer. “It takes three days to run the model on one budget scenario,” she says.

At Cape Lookout, OptiPres provided NPS with a breakdown of when and how best to take action for each of the modeled buildings. One thing that surprised Seekamp was that the action “Document and Monitor”—essentially letting nature take its course—was never recommended by the model. “It has such a negative impact on significance across the landscape to lose a building,” she says. This summer, Seekamp is taking OptiPres to Gulf Islands National Seashore in Florida, to test how well the model performs in a different context.

In general, planners and preservation officers seem to be undergoing their own adaptation processes, evolving to handle the newfound challenges of their own profession while also responding to the needs of the other. If resilience planners want more flexibility in adapting historic resources, preservation professionals want greater consideration of their community’s cultural heritage. Madeleine Helmer, a planner and historian at AKRF in Philadelphia, is more optimistic. “There doesn’t have to be this tension,” she says emphatically. “Integrating cultural heritage and adaptation planning can lead to more holistic, place-based, and effective adaptation efforts. Our adaptation strategies can be marks upon the landscape that will become meaningful in the future.”

In other words, the role of the designer really hasn’t changed. Turning the various constraints of a site into assets—one by one—has long been the landscape architect’s job. Rising sea levels and the dangers they pose are just another set of constraints. At the same time, sea-level rise has put the profession’s profile on a similarly upward trajectory, and the specter of more frequent flooding has only made green stormwater infrastructure and other landscape interventions all the more sensible, especially given their unobtrusive nature. A bioswale in the backyard or along the street is less disruptive than elevating the street or the properties along it. On a larger scale, landscape restorations, such as that of the Dyke Marsh Wildlife Preserve, part of the historic landscape along the George Washington Memorial Parkway in Virginia, become doubly important, bringing a much-diminished ecosystem back to what it once was and creating a more resilient and regenerative landscape buffer in the process.

Still, completed flood-mitigation projects that also preserve historic resources are few. “There’s been a heck of a lot more planning and thinking about adaptation strategies than actually implementing them,” says Veerkamp, of the National Trust. But a project in Saint Augustine, Florida, initiated as far back as 2001, offers some lessons in how to balance these competing needs. It also shows how doing so might just produce a landscape that is greater than the sum of its parts.

There are few places more historic and more susceptible to sea-level rise than Saint Augustine. Founded by the Spanish in 1565, it is the oldest continuously occupied settlement in the United States. In fact, the city’s form is so historically significant that the original town plan is a National Historic Landmark. But the low-lying city is also highly susceptible to coastal flooding, which puts it at ground zero for the potential obliteration of historic treasures at the hand of sea-level rise. In 2001, long before sea-level rise entered the public consciousness, a 100-foot section of Saint Augustine’s Avenida Menendez seawall collapsed in the wake of Tropical Storm Gabrielle. The city hired Halback Design Group (now Marquis Latimer + Halback) to develop a conceptual design for the stretch of waterfront in question, including a new seawall.

The old seawall, however, which remained intact along a portion of the waterfront, was a historic artifact, constructed by West Point cadets in the 1830s out of coquina stone, a soft material made out of crushed clam shells. Besides the wall’s own historic significance, the project site also fell within the boundaries of the Saint Augustine Town Plan Historic District. Because the coquina seawall would continue to degrade, it was determined that a new seawall was needed. But Fred Halback, FASLA, a senior principal at Marquis Latimer + Halback, also knew that the area’s landmark status meant that the state historic preservation office would have to sign off on whatever the team proposed. Halback’s solution was to preserve the existing seawall in situ and build a new, higher seawall roughly 12 feet seaward, creating a new waterfront promenade, with the old seawall visible and serving as a seating wall.

This is what was eventually constructed, though it took more than a decade to be realized (and by then Halback was not involved in the final design). Interestingly, it was the seawall’s historic significance that prompted the creation of the promenade. Had the seawall been just any kind of concrete retaining wall in a less historic part of the city, Halback says the city likely would have built the new seawall on the alignment, especially since expanding seaward required permits from the U.S. Army Corps of Engineers and other federal agencies. In fact, many people originally told him the plan was infeasible. “But our whole premise was that we have to move the seawall out because it’s the only way that we can protect the artifact,” Halback says. “And we used, quite candidly, the fact that we had this historic artifact that we wanted to preserve and enhance and interpret as our rationalization and our argument for ultimately getting all the different regulatory agencies to allow us to move the seawall out.”

Seventeen years after Tropical Storm Gabrielle, the original Avenida Menendez seawall is celebrated even as a new seawall protects it—and the city—from degradation. Halback’s firm is continuing to navigate the tensions between historic preservation and sea-level rise, most recently on a new mixed-use project within Saint Augustine’s historic downtown, where the design team helped mitigate potential flooding to such a degree that FEMA permitted the building to be built at an elevation a foot lower than recommended so that it would better blend with the historic streetscape.

Both projects are demonstrative of the pivotal role that landscape architecture can play in protecting historic resources from sea-level rise. “Landscape architects should be at the forefront of this discussion,” Halback says. “Because it’s not just about a building floating in space.”

CMG Landscape Architecture is at the beginning of a long journey toward its own inevitable reconciliation. Funded by a $425 million bond expected to pass this coming November, the first phase of the Embarcadero project could set the bar for resilience planning in San Francisco. Conger has many questions, but he is not dissuaded. He says his job is to synthesize the needs and desires of the community with the technical requirements of the engineering. “And then we’re going to find a solution that tries to do it all,” he says. “We have to make it seismically safe, and protect it from sea-level rise, and make a fantastic urban waterfront, and protect the historic resources. We have to do it all. So that’s what we’re going to do.”

Timothy A. Schuler writes about design, ecology, and the natural environment. He lives in Honolulu.