Land subsidence is a gradual settling or sudden sinking of the Earth’s surface (1).

Land subsidence is a gradual settling or sudden sinking of the Earth's surface owing to subsurface movement of earth materials. Subsidence is sinking of the Earth's surface in response to geologic or man-induced causes. The principal causes of land subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, dissolution of limestone, seasonal effects, and thawing permafrost.

Subsidence - sinking of the ground because of underground material movement—is most often caused by the removal of water, oil, natural gas, or mineral resources out of the ground by pumping, fracking, or mining activities. 

Subsidence can also be caused by natural events such as earthquakes, soil compaction, glacial isostatic adjustment, erosion, sinkhole formation, and adding water to fine soils deposited by wind (a natural process known as loess deposits). Subsidence can happen over very large areas like whole states or provinces, or very small areas like the corner of your yard.

Some cities sink because of the weight added by human beings. For instance, New York is sinking (2), and its skyscrapers are bringing it down. That's the finding of a new study that modeled the geology beneath the city compared to satellite data showing its footprint is collapsing into Earth.

This gradual settling or sudden sinking of Earth's surface occurs when soft sediments shift, or loads bearing down on the ground push it deeper still. There are many causes, but the weight of cities themselves is  really disturbing. 

And  every additional high-rise building constructed at coastal, river, or lakefront settings could contribute to future flood risk (2).

It also brings to mind the totality of human construction. As of 2020, scientists estimated that all the stuff humans have ever made was close to or already outweighing the dry weight of every last living thing on Earth. Buildings and roads weigh more than all trees and shrubs combined; plastics double the weight of animals (3).

Apart from the mass of buildings and their contents, the roads, sidewalks, bridges, railways, and other paved areas also contribute to subsidence. 

And the ground beneath a city is important too while measuring this sinking of cities. Modeling the behaviour of these substrates,  researchers showed clay-rich soils and artificial fill are particularly prone to subsidence. More elastic soils bounce back after construction, while bedrock, anchoring many skyscrapers, doesn't budge as much.

Comparing these models with satellite data measuring land surface height, researchers  map its subsidence estimates across any city. Increased urbanization, including the draining and pumping of groundwater, could only add to the subsidence problem, the researchers warn.

New York is certainly not alone in its subsidence. A quarter of Indonesia's capital, Jakarta, could be underwater by 2050, with parts of the city sinking by almost 11 centimeters a year due to groundwater extraction. More than 30 million Jakarta residents are now reckoning with the prospect of relocating the city or doubling down on climate action, such as opting for electric buses.

Other cities that are under more threat are Lagos (Nigeria), Houston (Texas, USA), Dhaka ( Bangladesh), Venice (Italy), Virginia Beach ( Virginia, USA), Bangkok ( Thailand), New Orleans ( Louisiana, USA), Rotterdam (The Netherlands), Alexandria (Egypt), Miami (Florida, USA) (4).

And in India, Mangalore in Karnataka, Kandla in Gujarat, Mormugao in Goa, Paradip in Odisha, Mumbai in Maharashtra, Kochi in Kerala, Bhavnagar in Gujarat, Tuticorin (1.9 feet), Khidirpur (0.49 feet), Okha 1.96 (feet), Chennai (1.87 feet, Tamilnadu) and Visakhapatnam (1.77 feet, Andhra Prades) are at risk (5).

These are not the only ones that are sinking. 

A 2022 study of 99 coastal cities around the world found that subsidence might actually pose a bigger, or at least underrated, problem compared to sea-level rise. In most cities surveyed, the land is subsiding faster than sea levels are rising, which means residents will be challenged by flooding sooner than climate models have projected.

While tons of skyscrapers have already been built, our planet's future trajectory is not set in stone – and reducing greenhouse gas emissions is the best bet we have to limit future risks, be they rising seas or hurricanes.

How to stop this sinking of cities?

Sustainable water management, restoring water ecosystems in cities, waterproof urban planning, pumping stations in low lying areas, reclaiming of natural waterways, creating buffer zones in suburbs and saving what is left of the floodplains,  are the solutions. 

Protecting shorelines of coastal sinking cities is crucial to preventing the sea from taking over. Building on stilts is another way to prepare for changing water levels. And compensated foundations can reduce the stress on a city's surface, which otherwise is a consequence of heavy loading. 

Rapid increases in population growth challenge the carrying capacity of these urban environments often leading to mismanagement of natural resources. For sinking cities, the most common result has been over-extraction of groundwater ultimately resulting in land subsidence. This should be stopped. Replenishing ground water is absolutely necessary. Urban planners should design cities in ways that avoid subsidence. This includes plenty of green places, such as parks, to allow natural groundwater replenishment from rain.

Constructing high rises and skyscrapers appropriately. In general, it is good to have a deep foundation of your building so that the weight is not compressing the soil and allows for enough groundwater to infiltrate. This keeps spaces open so that rainwater can fill in any void and reduce subsidence in that way.

Building high rises and skyscrapers on bedrock or hard soils helps prevent subsidence. He adds smaller buildings that do not need such a deep foundation will not subside as long as the mass of earth moved from underneath them is equal to its mass.

Listen to the experts and follow their advice. There is no other go. You cannot do whatever you want recklessly anymore on this planet.

Footnotes:

1. https://oceanservice.noaa.gov/facts/subsidence.html

2. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022EF003465

3. https://www.sciencealert.com/new-york-city-could-be-sinking-under-t...

4. https://www.weforum.org/agenda/2019/09/11-sinking-cities-that-could...

5. https://curlytales.com/sinking-cities-in-india-that-can-go-underwat...