apocalyptic stories about flood-swallowed train stations and drowned basements may be extreme, but for people living in densely populated urban areas on the coast, rising water levels are a reality. In fact, the city’s infrastructure often exacerbates storms since the paved ground cannot absorb the water. Storm runoff can further endanger residents and cause flash flooding.

It’s bad enough, and whether you live in New York or Seattle, it’s only going to get worse. The US coastline expects to see a one-foot sea level rise by 2050, according to the National Oceanic and Atmospheric Administration. Twelve inches of additional water would submerge a significant portion of land and leave the nation’s coastal communities increasingly vulnerable to flooding during extreme weather conditions like hurricanes. In total, more than 2.5 million US coastal homes and buildings, with a collective value of about $1.07 trillion, may live with disruptive flooding by 2100.

Engineers and city planners may try to minimize the damage, there’s a problem: preventative action requires years of planning ahead to be effective, and if you’ve ever lived in one, you know that cities aren’t predictable. In 50 years, who’s to say whether a given neighborhood will comprise sparse single-family homes or a dense cluster of condominiums? Will it be surrounded by parks or parking lots?

Most flood analyzes assume that current neighborhood layouts will remain the same in the cities of the future, says Anna Braswell, a coastal ecologist at the University of Florida. Reverse.

“We have these very static ideas of what the world is like,” she says. “The world is not static.”

What Zillow reveals about the cities of the future

A new study offers a little more clarity on how urban landscapes might evolve amid rising sea levels. Using data from the real estate company Zillow, environmentalist Braswell and her team traced two centuries of development in US cities, paying close attention to areas that are now most vulnerable to rising water levels.

The study was published in plus one.

The analysis reveals crucial trends in the growth of our coastal metropolises. Most concerning, the researchers found that by 2015, more than a third of the land within areas expected to rise up to six feet in sea level was developed for people to use and live on.

To try to understand why someone would build land that could soon be under water, Braswell’s team took a closer look at the family trend in the US that generally tended to expand before those inland.

To give you an idea of ​​how populated US coastlines are today, they found that between 1950 and 2000, these regions saw a 446 percent increase in new structures as the people who lived there developed a 220 percent more of the land. Suburban sprawl accounts for much of the work, as do Americans flocking to live in the Sun Belt states after World War II. In general, the areas most vulnerable to sea level rise have become more densely populated and have expanded at higher rates than inland regions.

The document notes that each region progressed in different ways. For example, along the Pacific coast, cities have developed a relatively small part of the land that is susceptible to sea level rise. The Southeast, for its part, has increasingly reinforced the population within these areas since the end of the 20th century.

Of all the regions, the Gulf Coast could become a future city hotspot because it has been the least used so far.

Todd BenDor, an environmental planner at the University of North Carolina who was not involved in the study, says he was impressed by the data set that Braswell analyzed.

“A big problem has been, how do you really study this without spending, without exaggerating, years just putting these data sets together,” said BenDor.

Much of Braswell’s work confirms trends already suggested or documented in other studies, reinforcing the need for the United States to accommodate its aging, vulnerable, and cramped coastal infrastructure. This is particularly relevant because coastal regions appear to have slowed their expansion and instead focused on reinforcing dense areas.

Working before the disaster

As Braswell and his co-authors point out in their new study, fundamental differences between regions of the US call for different solutions.

On the East Coast, for example, cities are already relatively full. Also, many of the houses and apartments were built before modern building codes were established. In these cases, retrofitting older buildings, taking what’s already there and making it disaster-proof, can be especially helpful.

In November 2021, for example, New York City announced a pilot program to retrofit its infrastructure against future weather disasters. One option they may consider: stormproofing underground pipes and conduits.

“New York is a perfect example of a place where many of the city’s arteries are located underground,” says Braswell, which could leave necessities like water or electricity defenseless in a storm.

The Boston government is also thinking ahead and has announced plans to flood-proof subway tunnels.

Meanwhile, the Gulf and West coasts may benefit from a different approach. After all, state and local governments in these areas have more opportunity to keep people out of harm’s way simply by prohibiting new construction in flood-prone areas.

In Florida, the Coastal Building Control Line regulates areas around beaches and dunes, requiring developers to locate new buildings relatively far from the water. New excavations must also be able to resist storm winds and storm surges, for example by supporting them high off the ground.

Cities can also work to modify flood insurance, which can discourage living in or constructing certain buildings. “How you set up those incentives really affects how these markets operate,” says BenDor. In some areas, generous flood payments or other policies may endanger more people by encouraging them to settle in dangerous areas.

A surprising and counterintuitive finding from Braswell: After a hurricane, you might think that cities in high-risk areas would reduce construction, but in fact they often tend to rebuild more densely, possibly due to older buildings and now damaged. buildings being torn down and replaced with newer ones.

In these cases, changes in building codes or regulations could limit new construction or ensure that buildings that spring up in crowded areas are prepared to withstand the next storm.

the biggest photograph

Solutions like stilts and repaired pipes are one factor in a more complex flood preparedness equation. After all, excess water needs a place to go. For that reason, some cities are creating reservoirs to help control flooding. Bangkok is building underground containers for water, for example, and in Rotterdam, the Netherlands, the government is turning ponds, garages and parks into emergency reservoirs. When a storm hits, the water will be channeled and trapped in these areas instead of rushing toward homes or businesses.

Other places are investing in ways to contain the sea, like in Tokyo, where the government has built “super dams” wide enough to fit entire street buildings, or the massive flood gates known as MOSE that now protect Venice. . However, this is not a new concept. Cities have also used land reclamation for centuries in countries like the Netherlands, where artificial islands were raised from the bottom of the sea.

Another option is what are known as “nature-based solutions”, which have recently been implemented around the world. Ho Chi Minh City in Vietnam, for example, created the Can Gio Mangrove Biosphere, which protects nearby mangrove forests. They also planted more trees and asked residents to participate in monitoring deforestation. In countries like the US, cities are planting useful vegetation or coaxing oyster reefs back.

For some communities, the best option may be to pack up and move, a strategy known as controlled retirement. It is often carried out by small groups, but the huge city of Jakarta, Indonesia, is now relocating more than a million people. By 2050, rising sea levels will force around 300 million people living in coastal areas around the world to relocate.

None of these solutions will be easy. Controlled removal, for example, can be devastating to the communities involved. And adaptation strategies have the potential to backfire and create new environmental hazards. Such risks will undoubtedly fall on low-income households and people of color, who often bear the brunt of environmental disasters.

While Braswell points out how further development around the world is inevitable and necessary to accommodate growing populations, mindful strategies can help communities adapt to incoming floods. “It’s a new concept that I’m not sure we’re really the best at cracking yet,” she says.