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| Cities that are sinking under the weight of their buildings |
In the US city of New York, the ground is sinking under the weight of buildings and it is not the only coastal city around the world that is facing this problem. As sea levels rise adjacent to these concrete jungles, the question is whether these cities can be saved.
September 27, 1889, was the day the workers finished work on the Tower Building. This 11-story building was New York's first skyscraper due to its steel structure.
The tower building is no longer there, but its construction started a tradition of similar buildings that has never ceased.
New York City's 300 square miles contain 762 million tons of concrete, glass, and steel. This estimate has been made by researchers of the US Geological Survey. It does not include the weight of furniture and other items in the building. Nor does it include the 8.5 million people who live in these buildings.
All this weight is having a surprising effect on the land on which these buildings are built. According to a study published in May, the ground in New York is sinking at a rate of one to two millimeters per year, partly due to the pressure of these buildings.
This is a matter of concern for experts. Considering the rising sea level, which is rising at a rate of three to four millimeters per year, this is a major problem for any coastal city.
Land subsidence is not a new phenomenon in New York, nor is it confined to this city. Tom Parsons works at the US Geological Survey's Pacific Coastal and Marine Science Center.
He says this is a global problem and New York should be used as an example of the same problem in other US coastal cities.
All cities, where people are settling in large numbers and where sea levels are rising, face the same problem, he says.
Why are coastal cities sinking? There are many reasons for this, but human constructions that put extra pressure on the land are also playing a role, and these constructions are becoming more numerous. In 2020, man-made objects had grown more than all living things combined.
Can anything be done before these cities sink into the sea?
Some cities in the world are sinking faster than others. They include Jakarta, the capital of Indonesia.
Oceanography professor Steven de Hondet says some cities are sinking at an average rate of a few centimeters a year.
De Hondet is one of the authors of a study published in 2022 that used satellite images to examine average land subsidence in 99 cities around the world.
He wrote that if land subsidence continues at the current average, these cities will experience severe flooding sooner than we expect.
The majority of the list of such cities is from Southeast Asia. Some parts of Jakarta are sinking at an average of two to five centimeters (two inches) per year.
It should be noted that Indonesia is working on building an alternative capital instead of Jakarta. Apart from this, Manila in the Philippines, Chittagong in Bangladesh, Karachi in Pakistan, and Tianjin city of China are also included in this list. These cities are frequently flooded.
Meanwhile, Mexico City is sinking at a rate of 50 centimeters per year. The city of Semarang in Indonesia is sinking by an average of two to three centimeters per year, while the northern part of Tampa Bay in Florida is sinking by an average of six millimeters.
Matt Wei says that some of this process occurs naturally, but is accelerated by humans. Not only the weight of the buildings but also the drainage of underground water and the process of extracting gases and oil from the ground.
Part of each of these processes can vary spatially, which complicates understanding land subsidence in coastal cities, Matt says.
One thing is certain that no matter how complicated this issue is, it has to be solved. Rising sea levels cause considerable damage even before a flood, a storm that will sink all boats.
De Hondet says the effects of sea-level rise first occur underground. Most of our infrastructure is buried underground, even the foundations of buildings, and seawater has effects on them that are visible on land much later.
But what is the solution? One solution is to stop further construction.
Tom says that the ground beneath buildings gradually settles after a year or two of construction. Therefore, according to them, it should be ensured that large buildings are built on a strong surface to reduce the subsidence of the land.
Another solution is to slow down the process of extracting water from the ground. Tom and his colleagues warn that population growth in cities will increase groundwater drainage and increase construction. Therefore, according to them, there is a need to find sustainable solutions to meet water needs.
However, another solution is to build walls along the coast to prevent flooding. Two works have been done to solve this problem in Tokyo, the capital of Japan.
On the one hand, walls, pump stations, and floodgates have been constructed along the coast, and on the other, emergency drills and flood early warning systems have been developed.
Often it is up to the citizens themselves to step up to solve their city's problems. According to a 2021 study, in Jakarta, Manila, and HoIn Chi Minh City, residents took matters into their own hands and took steps to avoid damage in the event of a flood.
One of the most effective steps was to build large underground water tanks to slowly release the floodwaters.
Martin Lumbley works for a company called Waven and specializes in water drainage.
He says that the problems of today's world are quite different from those when drainage systems were introduced in cities.
We may see an increase in innovation with rising water levels. In 2019, the United Nations discussed the concept of floating cities at a meeting.
Halting climate change by cutting greenhouse gas emissions can also slow sea-level rise.
"Governments should be worried," says de Hondet. If we want to avoid a major disaster in a few centuries, we need to plan now.