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Study reveals that 34 million people live on unstable terrain - the ground is sinking in cities such as New York, Chicago and other major US metropolises
Sidewalks are cracking, streetlights are leaning, and walls are cracking. Many residents see these as signs of normal wear and tear. But in many U.S. cities, the problem is more serious: the ground is sinking.
And, according to a new study published in the journal Nature Cities, this is happening in all 28 of the most populous cities in the US.
Millions live on unstable ground
The research indicates that the phenomenon, called subsidence, affects 34 million Americans. This sinking of the ground occurs slowly, often without being noticed. The main cause is not earthquakes or erosion, but rather the excessive withdrawal of water from US underground aquifers.
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With the help of satellites, researchers have detected that in 25 of the 28 largest American cities, more than 65% of the urban area is sinking. And in cities such as New York, Chicago, Detroit and Dallas, this rate exceeds 98%.
Houston leads urban subsidence
The worst case is Houston, where 42 percent of the area is sinking at a rate of more than 5 millimeters per year. In some neighborhoods, the rate is more than one centimeter per year. That may not seem like much, but that represents about 30 centimeters in three decades — enough to undermine entire buildings.
Subsidence isn’t just happening in peripheral areas. It’s also affecting urban areas with critical infrastructure. LaGuardia Airport in New York City is sinking. The same is happening in parts of San Francisco and even East Potomac Park in Washington, D.C.
Water shortage, soil collapse
The main cause identified by the study is the excessive use of groundwater. Removing this water reduces the pressure that keeps the soil stable.
When this pressure decreases, the ground begins to compact. In some cases, the collapse can be irreversible, especially in aquifers confined between layers of clay and rock.
The study reveals a direct link between falling groundwater levels and land subsidence in at least 13 cities.
The most worrying examples are in New York, San Diego, Houston and Memphis. In New York and San Diego, 76% of the vertical ground movement can be explained by these changes in water pressure.
Geology also influences the rate of sinking
Local geology also plays a role. In San Diego, the aquifers are highly permeable, which speeds up the process. In Washington, DC, the bedrock offers more resistance. However, it does not guarantee complete protection.
More than 29 thousand buildings in risk zones
The impact is tangible. More than 29 buildings are in areas at high or very high risk due to subsidence.
Many are subject to what is called differential ground movement — when one side of the structure sinks more than the other. This can cause cracks, affect foundations and compromise bridges, roads and homes.
In cities like Austin, Fort Worth and San Antonio, the structural risk is even greater. Between 1 in 45 and 1 in 143 buildings in these locations are at risk. Even a slight tilt of just a few millimeters per year can have serious consequences over time.
Silent and often invisible damage
The study highlights that the problem varies greatly between cities and even between neighborhoods. Soil composition, construction methods and the type of foundation make a difference. However, the risk exists and, according to the authors, is being underestimated.
Recent cases of landslides have highlighted the fragility of urban infrastructure. However, the damage caused by subsidence often goes unnoticed until it becomes serious. The study suggests that this process may be silently weakening many buildings in the country.
There are ways to act and avoid the worst-case scenarios
The good news is that some of the problem can be controlled. While some causes are natural, much of the subsidence is caused by human actions. This means that measures can be taken.
The first step is to improve groundwater management. This includes limiting pumping, promoting responsible use, and investing in aquifer recharge technologies. In some places, it is possible to store surface water underground during periods of rainfall.
Planning for the future with data and adaptation
Another essential measure is to map risk areas. Satellite data helps, but more detailed local studies are essential. They allow for a better assessment of the soil and adaptation of construction plans according to the risk.
U.S. cities also need to adapt. In flood-prone regions, subsidence can exacerbate the effects of rainfall and tidal surges. Raising infrastructure, banning construction in certain areas, and improving drainage systems can help mitigate the impacts.
Call for immediate action
The study concludes with a clear warning: subsidence needs to be taken seriously. Urban planners and authorities must consider this factor at every stage of decision-making. Otherwise, the damage could multiply and become irreversible.
With information from ZME Science.
