MOSCOW, May 24, Vladislav Strekopytov. New York is sinking at a rate of several millimeters per year. The reason is giant skyscrapers built on shaky ground. According to scientists, subsidence threatens another 99 large metropolitan areas. There are no Russian cities in this list yet.
Under its own weight
Scientists from the US Geological Survey and the University of Rhode Island, after analyzing satellite altimetry and ground-based geodetic observations over the past few years, came to the conclusion that the earth's surface in New York is sinking an average of one to two millimeters a year. The simulation results showed that this is due to soil subsidence under the weight of buildings and infrastructure.
Previously, flood forecast models only took into account global sea level rise, which is three to three and a half millimeters per year. It is now clear that subsidence may be an equally important factor.
The researchers calculated the total weight of New York structures — almost 770 million tons. This is without taking into account roads and railways, sidewalks, bridges and other infrastructure. Then the authors divided the city into cells with an area of 100 by 100 meters, calculated the pressure of buildings in each and compared it with the type of soil. It turns out that in certain areas, such as Lower Manhattan, Brooklyn and Queens, where skyscrapers line the coastline and rest on a base of sand and clay, the rate of subsidence reaches six millimeters per year.
Moves can create a serious problem for the largest metropolis in the United States. Firstly, from such displacements and the penetration of salt water into the base, skyscrapers simply collapse. Secondly, the risk of flooding is increasing. Much of Lower Manhattan is only a meter or two above sea level. Hurricanes 2012 (Sandy) and 2021 (Ida) showed how quickly the area can be completely under water.
The researchers warn that measures that are usually proposed to protect against possible flooding (the construction of coastal embankments, drainage and pumping of groundwater) in this case will only exacerbate the problem. They work effectively where buildings rest on hard bedrock, which in New York only comes to the surface in the very north, in the Bronx and in Upper Manhattan. The main part of the city, in geological terms, is a complex of loose coastal, lacustrine and glacial deposits — sand, clay, silt and glacial moraine. This type of soil, in principle, is not intended for the construction of large structures.
«Each new high-rise building erected on the coast increases the risk of subsidence and flooding in the future,» lead researcher Tom Parsons of the USGS said in a press release. />
Water all around
A similar situation is typical for many other metropolitan areas. In San Francisco, for example, another study by Tom Parsons showed that the compaction of loose, porous base rocks resulted in groundwater squeezing out and an overall lowering of the surface by about 80 millimeters.
Scientists from the University of Rhode Island analyzed satellite altimetry data for 99 major coastal cities of the world for the period 2015-2020. The results showed that most are sinking faster than sea levels are rising, meaning residents will face the risk of flooding sooner than climate models predict.
Chinese Tianjin (40 millimeters per year), Chittagong in Bangladesh and the capital of the Philippines Manila (20 millimeters per year), as well as Pakistani Karachi (ten millimeters per year) are leading in the rate of sinking. The combined population of these four cities is 59 million people. Major cities such as Istanbul, Lagos, Taipei and Mumbai are sinking by more than two millimeters a year.
According to the latest report of the Intergovernmental Panel on Climate Change (IPCC), due to local problems and general sea level rise due to global warming, at least nine major cities may be partially under water by 2030 — Jakarta in Indonesia, Kolkata in India , Ho Chi Minh City in Vietnam, Lagos in Nigeria, New Orleans in the USA, Rio de Janeiro in Brazil, Osaka in Japan, Venice in Italy and Rotterdam in Holland. Now New York has been added to the list.
The worst situation is in Jakarta, the capital of Indonesia. In a city with 11 million inhabitants, there is no central water supply; residents build wells and boreholes on their own to pump water from there. As a result, voids and dips are formed in the rocks. In some areas, the surface of the earth is sinking at a rate of up to 11 centimeters per year.
Now the uncontrolled pumping of water has been stopped, but the soil is still sinking. If this continues, by 2050 a quarter of Jakarta's territory may be under water. The government is building a coastal fence along the northern part of the city, and is also seriously discussing the project of moving the capital to the island of Kalimantan.
Overexploitation of underground aquifers is the most common cause of subsidence in other cities as well. In Tianjin, the northeastern part of the city is sinking at a record pace, where numerous enterprises using underground water are located. The same situation is in Indonesian Semarang and American Tampa.
Destructive urbanization
Traditionally, large cities were built on the coast. Now many of them are overpopulated, including in developing countries where urbanization is taking place at a rapid pace. 37 percent of the world's population already lives within 100 kilometers of the coastline. But it is this area that is especially vulnerable to sea level rise and erosion, and the loose soils here are usually ill-suited for the construction of high-rise buildings.
The most striking example of uncontrolled urbanization is Lagos, the capital of Nigeria, the country with the highest population growth rates in the world. The city is sinking at a rate of two to 87 millimeters per year. Partly due to groundwater pumping, but most rapidly in coastal areas where heavy structures are built on weakly cemented sediments.
In Ho Chi Minh City, Vietnam's largest metropolitan area, population growth is also exceeding infrastructure capacity. Central water supply does not have time to bring to new buildings, residents use their own pumping wells. Chaotic development destroyed most of the natural channels, as well as islands of nature in the city, and the soil stopped holding water. Because of this, new houses shrink, which threatens to collapse.
The water in the Saigon and Mekong rivers that cross Ho Chi Minh City has risen by 80 millimeters over the past 20 years. At the same time, almost half of the metropolis is located at an altitude of less than a meter above sea level. Residents move houses on piles, and the authorities raise roads. There are similar problems in the country's second largest city, Hanoi.
Scientists propose to declare the risk of floods in large coastal cities as a global threat, which is growing every year as urbanization and general warming on the planet continue. According to experts, by 2040, 12 million square kilometers of land, which is home to 19 percent of the world's population, will be below sea level. This will also hit the global economy hard: these territories account for 21 percent of the world's gross domestic product.