A recent study published in the British journal Nature Cities on May 8 highlights a concerning trend in American urban areas: sinking cities.
According to the research, 25 out of 28 of the most populous cities in the United States are experiencing varying rates of land subsidence.
While coastal cities are often thought of as the most vulnerable due to rising sea levels, this study reveals that many interior cities are also facing similar challenges.
Notably, in every city analyzed, at least 20% of the urban area is sinking, and for 25 of the 28 cities, that figure rises to at least 65%.
Boston finds itself among these affected cities, with data indicating that over 72% of its land area is sinking at rates of up to 3 millimeters annually.
Moreover, around 0.3% of the city is subsiding at even greater rates.
This phenomenon impacts a staggering 535,231 residents, with over 80% of Boston’s population directly exposed to the risks associated with land sinking.
The primary driver of this subsidence in Boston and other cities is substantial groundwater extraction.
Groundwater withdrawal from aquifers, particularly those composed of fine-grained sediments, leads to a collapse of the pore spaces that were once filled with water.
As the water is extracted and not replenished, the land above can become compacted, ultimately resulting in sinking at the surface, according to experts from the Lamont-Doherty Earth Observatory.
In addition to natural subsidence, coastal areas may also experience exacerbation due to activities such as sand mining and dam construction.
Other regions, like Texas, see accelerated sinking from oil and gas extraction practices.
Leonard Ohenhen, the study’s lead author from Lamont-Doherty, notes that land subsidence can have serious repercussions on infrastructure.
As the ground shifts, the integrity of buildings, roads, and bridges may be compromised.
Many early warning signs often go unnoticed but include symptoms like cracks in walls, sloped floors, improperly closing doors and windows, warped roads, and tilting fences or utility poles.
Houston has been identified as the fastest-sinking city in the nation, with over 40% of its area sinking more than 5 millimeters per year.
Additionally, cities like Fort Worth and Dallas, also in Texas, are not far behind in terms of subsidence rates.
Localized areas such as East Potomac Park in Washington, D.C., and LaGuardia Airport in New York are also experiencing notable sinking, with rates reaching up to 5 centimeters per year.
Looking ahead, researchers warn that continued population growth, coupled with increased water usage and climate-induced drought in specific areas, is likely to worsen subsidence issues in the future.
Ohenhen emphasizes the importance of proactive measures, stating, “As opposed to just saying it’s a problem, we can respond, address, mitigate, adapt.”
In Boston, where both land subsidence and sea-level rise pose significant threats, the study suggests a variety of strategies including protection, accommodation, retreat, and possibly acquisition to tackle these challenges effectively.
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