Dire sea-level rise predictions call out for landscape design solutions.

By Zach Mortice

The Union of Concerned Scientists’ recent report on the economic damage and displacement that sea-level rise flooding will unleash called for investments “in a range of coastal adaptive measures,” such as “the protection of wetlands, and barrier islands, and other natural flood risk reduction methods” and other “natural infrastructure.” That puts the onus of surviving sea-level rise very clearly on landscape architects.

The report, Underwater: Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate, which the Union of Concerned Scientists (UCS) compiled with help from the real estate website Zillow, shows the consequences of sea-level rise in the short and long term, down to the state, city, and zip code levels of granularity. Released in June, it estimates lost houses, lost home value, lost tax base, and lost population by the years 2035 and 2100.

The report defines chronic disruptive flooding as inundation that happens 26 times per year or more, and projects that in approximately the next 15 years, coastal flooding will wipe out $63 billion of housing wealth, affecting 280,000 people. In the next 30 years (the life of a standard mortgage), 300,000 houses could be lost. By the end of the 21st century, with a projected 6.6 feet of sea-level rise, 2.5 million residential and commercial properties will be chronically flooded. This will add up to losses of $1.07 trillion (the gross domestic product of Florida) and affect 4.7 million people (equivalent to the population of Louisiana).

The report also outlines mitigated climate change scenarios—increasingly less viable options—in which global emissions stay within the 2 degree Celsius limit established by the Paris Agreement. This would avoid losses of $780 billion and allow 4.1 million people to keep their houses.

If this sounds impossibly dire, it’s important to remember that the UCS report is actually a conservative estimate. It doesn’t incorporate rising groundwater levels that are abetted by sea-level rise, which will flood basements before the oceans encroach. The full scope of the calamity will likely be much worse.

However, “There’s no reason that we should sit around and watch this coming,” says Erika Spanger-Siegfried, a lead climate analyst with UCS and an author of the study. “We have plenty of advanced notice on this.”

Flooded municipalities and the homeowners in them can decide to defend their properties against further inundation, accommodate floodwaters while still staying put, or retreat from the shore, but all of these approaches have landscape design ramifications. “Really thoughtful landscape design,” says Spanger-Siegfried, “is going to be an essential piece of our response to this problem.”

The UCS report details market and regulatory incentives that push homeowners toward ad hoc responses when flooding occurs, based on optimistic assumptions that flooding will be an exceptional event in the years ahead. That means flood defenses that will allow life to continue just as before are often seen as the only viable option. “We suspect our impulses as human beings and our resistance to change [mean that] we’re going to want to defend straight out of the gate,” Spanger-Siegfried says. But walling cities off from the sea would incur costs far higher than “society would be willing to bear in terms of landscape and ecosystem losses,” she says. Insensitive sea-level rise adaptations could also destroy priceless historic buildings and landscapes, as detailed by Timothy Schuler’s recent LAM story, “Balancing Act.”

Kristina Hill, ASLA, a landscape architecture professor at the University of California, Berkeley, studies how urban areas can adapt to sea-level rise. She says affluent, high-density areas should be the focus of intense adaptation measures, because they’ll have resources to perfect these systems. “We’ll learn from what they try,” she says. “That’s the big advantage the Dutch and the Germans have had.”

Miami Beach, Florida, stands to lose 88 percent of its houses by 2100. It has gained a reputation as a progressive leader in combating sea-level rise with the resources to try new strategies, such as raising the level of its streets and installing new drainage pumps. Florida (with 64,000 houses at risk) and New Jersey (with 62,000 houses at risk) are the most vulnerable states in the nation, but may not wholly recognize that these properties are imperiled. Some 15 to 20 percent of houses at risk in these two states were built after 2000.

The amount of money and resources available to deal with sea-level rise vary wildly by location, and the UCS report looked specifically at the added layers of vulnerability underserved populations (identified by income, race, and age) face. Intense overlap was found between marginalized groups and the likelihood of flooding. By 2045, 40 percent of communities at risk will have poverty levels above the national average. “We need to make sure we are mobilizing resources for those who need it most,” Spanger-Siegfried says.

And the stripping of wealth along the coasts is likely to become more entrenched. Recent research from the Harvard Graduate School of Design showed that in Florida’s Miami-Dade County, there is a positive correlation between appreciating property values and higher elevations, and that properties at higher elevations have prices that appreciate faster than those at lower elevations. The study outlined the theory of “climate gentrification,” where affluent real estate shoppers and developers can push out lower-income residents (who are often renters) living at higher elevations as floodwaters advance on luxury beachfront condos.

This cratering of real estate values for the rich and poor alike points to past economic calamities that began with the real estate market but didn’t stay there; that’s just how the Great Recession began. But there’s one key difference: Unlike in past recessions, there’s no reason to expect property values to rebound eventually. The water will drown what is most people’s largest investment forever.

Current policies for flooding and climate change don’t spend much time or money preparing plans to get out ahead of this slow-moving disaster. But Spangler-Siegfried’s report offers a set of policy prescriptions that can create the regulatory tools needed by landscape architects (or any other profession) to discourage maladaptive developments and push forward resilient ones. These include mandatory flood risk disclosure, restructuring post-disaster aid to prevent future floods, revamping the National Flood Insurance program, and offering more funding for voluntary home buyouts. However, all of these are difficult sells to a presidential administration that doesn’t acknowledge climate change.

And whereas the public sector response to climate change lags, some areas of the financial sector are building traumatic flooding into their plans for the future. UCS gathered input from banks, real estate officials, commercial property investors, and credit rating agencies, all of whom understand the inevitability of sea-level rise. (See Brad McKee’s LAM Land Matters column, “Credit Only Where Due.”)

As landscape designers develop more ways to shield cities and towns from floodwaters and deploy soft wetland edges to soak up storm surge, there’s still a job to do even when the best course of action is to cede the shoreline back to the ocean, says Hill. Remediation has to follow in humankind’s wake, even if humans are no longer there. “In many urban places, we’ve polluted the soil, and we’d be leaving pipes behind, and landfills, and gas stations,” she says. “It’s not an environment that’s going to be good when the sea reclaims it.”

For inspiration, Hill looks to the Bay Area’s success at levying a new tax to pay for restoration of 40,000 acres of salt marshes. In Japan, “super levees” elevate massive plots of urban land from floodwaters and use terraces to slow the flow of water in case they’re overtopped. Hill looks forward to adaptation strategies such as floating houses situated on “urban blocks that are connected on a shared decking with pontoons underneath” that are up to three to five stories tall.

But any solution for sea-level rise in residential areas has to confront the extreme atomization of ownership and diffusion of decision making that make collective action in the real estate market grueling. UCS collected data on nearly 4,000 coastal municipalities. There are few institutions that can make wholesale changes to land use—an intensely local issue—from coast to coast. Hill says that designers and policy makers have to find surgical ways to tap into the public sector’s purview, such as using the design and construction of roads (ideally located between the sea and settlement) as flood mitigation infrastructure.

“This is not something that any individual community is going to grapple with on its own,” says Spanger-Siegfried.

Zach Mortice is a Chicago-based design journalist who focuses on landscape architecture and architecture. You can follow him on Twitter and Instagram.