These Five Cities Are Vulnerable To Rising Seas, Including Miami and New York

The Thwaites Glacier is about the size of a U.S. swing state and holds enough ice to raise sea levels by about 10 feet. This alone is scary enough to justify its nickname, the Doomsday Glacier, but there's more. The Thwaites sits along a 75-mile stretch of shoreline in Antarctica that serves to partially shield the vast West Antarctic Ice Sheet from the warm ocean waters. The WAIS has enough ice to raise the seas by 200 feet.

Forty years ago, the Thwaites was thought to be shedding 40 billion tons of water each year. Scientists recently upped that figure to 250 billion tons. To their alarm, a river of warm water appears to be flowing beneath the glacier, which can only hasten the day when it collapses into the sea—it could be a century from now, or a few decades. No one really knows.

We haven't even talked about Greenland yet. Another underground river of warm water was recently discovered under the Nioghalvfjerdsfjorden Glacier, which is expected to add between a foot-and-a-half and 5 feet to ocean levels in the next 200 years.

These projections carry some uncertainty, but one thing seems pretty clear: the next century will be tough for coastal city dwellers. Sea levels are rising about 3 millimeters each year. By the end of the century, the oceans could rise at least 2 feet over 2005 levels, according to a 2018 study in the Proceedings of the National Academies of Science. Michael Mann, a climate scientist, told NBC News that unless emissions of greenhouse gases are abated, by the end of the century more than 650 million people will be living on land that is under water all or much of the time.

Cities will take the brunt of the impact. The last big survey by the World Bank of cities around the world that are vulnerable to climate change was published in 2013, based on satellite data captured in 2005. It found that hundreds of coastal cities around the world will be at heightened risk of flooding in the next few decades. In the years since the study was published, risk calculations have changed for the worse, says Stephane Hallegatte, lead economist at the World Bank's global facility for disaster reduction and recovery and an author of the report.

One change is that cities in Africa have grown quicker than expected. That means that any list of vulnerable cities would now have to include new names, like Lagos in Nigeria and Dar es Salaam in Tanzania. A dangerous combination of rising seas and poverty make these cities increasingly vulnerable. Many of the cities on the original 2013 list have improved their prospects greatly by taking steps to protect themselves against flooding. These include Guangzhou and Shanghai in China, Manila in the Philippines, Can Tho in Vietnam and New Orleans in the U.S.
Some cities in the developed world haven't adequately addressed the rising threat. In particular, Miami and New York are vulnerable to storm surges that bedevil the east coast of the U.S., and neither has implemented adequate protections. They would do well to take a page from London, Amsterdam and Rotterdam, which have invested in dykes, barriers and drainage systems.

The graphic below, provided by Statista, illustrates how rising sea levels will threaten populations around the globe by 2100.

The worsening outlook on sea-level rise is prompting a change in how people think about flooding and plan for it. "People realize that it's just not possible to prevent all floods, so you have to learn to live with the water and accept that it will sometimes have an impact," says Hallegatte. "We cannot live behind taller and taller walls, because at one point, the consequences of one of those walls failing becomes too big."

The Netherlands is at the forefront of new living-with-water techniques. They are building spaces in their cities for flood water to collect—areas of low density that are relatively easy to evacuate—to protect areas of high population density. They are using the dynamics of the river deltas to distribute sand in such a way that maintains protective dunes. Such quasi-natural systems are both less expensive to build and fail more gracefully than a big wall. "It's what we call nature-based solutions," he says. "Instead of trying to use concrete to just protect everything, you try to use natural mechanisms."

"We see people from all continents, all income levels, asking the same question: how to manage increased flooding over the next 10 or 20 years," says Hallegatte.

Here are five cities that have grown relatively more vulnerable in the last few years.

Dar es Salaam

Dar es Salaam, the former capital of Tanzania, is home to 4.3 million people and is one of the fastest growing cities in the world. People are leaving the countryside in pursuit of jobs, better schools and access to healthcare. When they arrive, they tend to settle on flood-prone land.
The city is not planning for the impact of extreme weather events that come along every few years because its problems are more immediate: it is beset by chronic flooding that comes with heavy rainfall each year. Although Tanzania
has worked to build a network of drainage canals to the Indian Ocean, these measures haven't solved the flooding problem in Dar es Salaam. Sea-level rise has meant that waters take longer to find their exit from the city. Garbage often blocks the drains, allowing stagnant water to collect. The city does not have the resources for big infrastructure projects. But recently, community groups have formed to clear the drains when heavy rainfall is in the forecast.

Jakarta

Like Dar es Salaam, Jakarta is also prone to yearly flooding during the rainy season. Several rivers flow through the metropolitan area and frequently overcome their banks. Compounding the problem of sea-level rise is subsidence: the city itself is sinking. The river delta, upon which the city rests, has been losing sand; the presence of the sprawling city prevents the sand from being replaced naturally by the rivers. Heavy buildings and the extraction of fresh water for drinking have compressed the sand further.

Jakarta has struggled to find resources to build the infrastructure it needs to mitigate flooding. Last fall, a plan to purchase land along the river for the construction of flood-prevention walls was canceled to plug a budget deficit. In 2015, the city installed concrete walls along the Ci Liwung River, evicting settlers and moving them to permanent shelters, but it wasn't enough to prevent flooding in the heavy rains earlier this year. More than 90,000 people had to be evacuated from Jakarta and more than 60 people lost their lives in the disaster.

Government officials in Indonesia announced a plan last August to move the nation's capital from Jakarta to Borneo.

Lagos

The population of Nigeria,Africa's biggest nation, is on track to double to 400 million by 2050, when most of its citizens are expected to live in the cities. Lagos is the biggest—its population, now estimated between 14 million and 21 million, is expected to top 30 million by 2050.

Lagos is already struggling under the weight of population growth, extreme weather and poor infrastructure. People moving to the city for a better life tend to settle on low-lying land that is prone to flooding. Every rainy season, rainwater mixes with sewage and floods homes, triggering outbreaks of respiratory and other diseases.

Development has been focused on building high-rise buildings to handle the burgeoning population, but these are out of reach for many people in flood-prone areas. Improvements in housing stock across the board are sorely needed. A lack of infrastructure to mitigate the frequent flooding has inhibited investment. If the city can overcome this catch-22, it may be able to turn its attention to protecting the city from the extreme storms that come along every few years.

Miami

Miami has been called ground zero for sea-level rise. South Florida is expected to be hit hard in the coming decades. Flooding in the city has increased in frequency in recent years, and the projections for sea-level rise suggest that many beaches and neighborhoods will eventually be fully submerged.

Barricading itself against the rising seas is not an option for Miami. Not only would a big wall disrupt tourism, it would also be ineffective. The city is built on limestone, which is porous—sea water can simply rise up through the ground.

In recent years, Miami has begun to take steps to prepare for its watery future. It raised a stretch of seawall breached in a storm a few years ago. It is also raising roads and bridges and investing in pump stations in neighborhoods that are prone to flooding. It is also designing a new storm-water drainage system to cope with hurricanes. It has imposed height requirements for new buildings.

Although these measures may help in the short term, coping will be a challenge in the coming decades.

New York

In 2012, Hurricane Sandy sent about 10 feet of floodwater to New York City, inundating tens of thousands of buildings and threatening the city's $2 trillion in assets. The water came mainly from the swell of Atlantic seawater that tends to push up against the U.S. eastern seaboard during big storms. As sea levels rise, the city is expected to see flooding in excess of 7.5 feet with increasing frequency—flooding that now occurs once every 25 years will happen every 5 years, according to a 2017 study. By 2050, more than a third of the city's financial district will be at risk for flooding from storm surges.

The Big Apple has made piecemeal investments to harden itself against future storms but has yet to enact comprehensive measures. Mayor Bill DeBlasio announced in 2019 a $10 billion project to extend lower Manhattan into the East River and build movable flood barriers. Other plans have called for seawalls, sand dunes and other structures. But time is short. If calamity strikes again anytime soon, New York will take a big hit.

This article was updated to include an infographic.