From shifting tectonic plates to prehistoric legacies, these cities could be "swimming with the fishes" by the end of the century if solutions can't be found.
What city is sinking the fastest?
According to a study called "Sinking Cities" by Dr. Katherine Kramer, the world's fastest sinking city is Jakarta in Indonesia. To date, 40% of the city has already succumbed to rising waters.
As it turns out, the city is sinking at an incredible 25 cm a year!
Jakarta lacks a reliable network of piped-in water, causing many the city's inhabitants building and using private, unregulated, water wells.
According to The New York Times, this causes underground aquifers to become drained, “like deflating a giant cushion underneath the city.”
This has led to a double-edged sword of issues for the city. Heavy rains regularly flood the city's neighborhoods and its heavy development (especially abundance of skyscrapers) are compromising the city's weak, and groundwater drained foundations.
What European cities are sinking?
Believe it or not, various European cities are currently sinking. This might sound crazy, but it is indeed true.
Some of the most notable European cities that are experiencing large-scale subsidence include, but are not limited to:
- Venice, Italy (of course)
- Rotterdam, The Netherlands
- London, The United Kingdom (more or this later)
Is New York City sinking?
It most certainly is. According to a study reported in Scientific American, New York could, by 2100, have sunk around 5 feet (12.7 m).
Its problems are very similar to those of other sinking cities like London.
"Since North American glaciers began retreating 20,000 years ago, the crust from New York City to North Carolina has been sinking, as the larger continent continues to adjust to the unloading." - Scientific American.
New York's woes are also not helped by its insatiable groundwater extraction and proximity to two large rivers that have a tendency to flood.
What cities are sinking?
So, without further ado, here are 7 of the world's most notable sinking cities. This list is far from exhaustive, we are sad to say.
It is also in no particular order.
1. Shanghai, China
Shanghai is, believe it or not, one of the world's fastest sinking cities. According to sources like EcoWatch, the city is sinking at a rate of around 1 cm per year.
The main cause of the subsidence is groundwater extraction.
This is dramatically down from only a few decades when rate whereas high as 9 cm a year. This dramatic improvement was achieved by local officials requiring official permits for any water wells from 1995.
The city is also losing sediment that would naturally protect it as its rivers are dammed and sediment is used as a construction material.
2. Mexico City, Mexico
Mexico City is one of the world's sinking cities. Groundwater extraction is, according to EcoWatch, causing the city's water table to drop at around 38 cm a year in places.
Over the last 60 years, the city has actually subsided around 9.8 meters or so.
As water is extracted from under the city it leaves empty spaces where the water once was. Over time this is compressed by the weight above, resulting in subsidence.
Another contributing factor is the fact that the city was once built on a drained lake within an old volcanic crater.
3. Bangkok, Thailand
Bangkok is yet another of the world's sinking cities. In fact, the city could be in serious danger of becoming irreparably sunk within the next decade or so.
It is currently sinking at around 2 cm a year.
A 2015 government report predicted the city will likely be underwater by around 2030. The main culprit, like other cities on this list, is groundwater extraction.
Action has been taken to attempt to mitigate this problem such as the 1977 Ground Water Act that has attempted to restrict the practice. Groundwater extraction rates have been reduced and water is also being pumped back underground.
But these measures might not be enough to save the city in the long run.
4. Venice, Italy
Best known for its extensive waterways and romantic history, the city is built in a muddy lagoon with inadequate foundations.
This is causing the ground beneath the city to compact over time. Combined with gradual sea level rises over time, the city is slowly being reclaimed by nature.
It has a relatively low population when compared to other cities, which means groundwater extraction is less of a problem for the city but isn't helping matters.
5. Lagos, Nigeria
Lagos in Nigeria is another city sinking under its own weight. The city was built on the coast and incorporates a series of islands.
The city suffers from poor drainage and is under constant threat of flooding. One 2012 study showed that just a sea-level rise of 1 to 3 meters would be catastrophic for the region.
Its large population also consumes huge amounts of groundwater every year leading to series subsidence over time.
6. London, The United Kingdom
The famous and iconic British capital of London is another of the world's sinking cities. Unfortunately for the city's officials, the problem is a legacy from the city's prehistoric past.
During the last ice age, enormous glaciers covered much of Northern Europe. Their weight pushed the Earth's crust in Northern regions like Scotland, resulting in relative rises in the land to the South.
Once the glaciers melted, the crust "rebounded" resulting in Scotland rising at around 1 mm a year. London, on the other hand, is sinking at around the same rate - making it increasingly prone to sea-level rise.
As a result, the enormous Thames Barrier, that first opened in 1984 to mitigate this issue, was expected to only be used 2-3 times a year to protect it from one-in-100-year floods.
In fact, it is currently being used around 6-7 times a year.
7. Dhaka, Bangladesh
Dhaka in Bangladesh is yet another city sinking under its own weight. Currently sinking at around 1.5 cm a year, the cities woes are a combination of plate tectonics, groundwater extraction, and sea-level rise.
The Bay of Bengal is rising at around 10 times the global average which has already resulted in millions of people migrating from surrounded coastal villages to the city's slums. This population needs to be supplied with potable water leading to excessive groundwater extraction that isn't helping the situation.
The Indian plate and Burman sub-plate are also interacting in such a way as to further compound the city's sinking problems.