New research reveals that every major city is slowly sinking.

A comprehensive study published in natural cities has found a shocking reality: all the largest metropolitan areas in the United States are gradually trapped under them.

The study analyzed high-resolution satellite data in 28 most populous U.S. cities and found that extensive land settlement affected urban areas from coast to coast. Although coastal cities have long been concerned about ocean rise, this phenomenon poses a unique threat to infrastructure across the country, as different regions of cities sink at different rates – sometimes putting dangerous pressure on buildings, roads and utility systems. About 34 million Americans currently live in affected areas, and this discovery calls for urgent attention to this slow but potentially destructive hazard.

Extensive settlement of cities across the United States

The research team, led by Leonard Ohhen of the Columbian climate school Lamont-Doherty Earthervatry, uses advanced satellite technology to map vertical land motion with unprecedented accuracy. Their analysis covers all U.S. cities with a population of more than 600,000.

“As cities continue to grow, we will see more cities expand into lurking areas,” explains Ohenhen. “As time goes by, this settlement creates pressure on the infrastructure, which will exceed its security limits.”

The study shows that of the 28 cities examined, two-thirds or more of the 25 cities are sinking. Among the most affected metropolitan areas, cities in Texas account for the fastest rankings.

Potential rates for Texas cities

Houston is the fastest major city in the country, with over 40% of its area exceeding 5 mm (about 1/5 inch) per year, while 12% sinks twice that speed. Some isolated spots fall as much as 5 cm (2 inches) each year. The overall settlement rate for Fort Worth and Dallas is not far.

Other cities showing locally rapid sinking include areas around LaGuardia Airport in New York and parts of Las Vegas, Washington, D.C. and San Francisco.

The main culprit behind this widespread urban settlement is human activity. The researchers determined that based on county-level groundwater evacuation data, using it for human use caused about 80% of the overall sinking.

Various forces driving the decline

Although excessive groundwater pumping occurs as a major factor in settlement in most cities, several natural forces also contribute to this phenomenon:

• The lingering effect of the ancient ice sheet that once covered North America is still causing a portion of the landscape to gradually settle
• The huge weight of city buildings may be pressing against the earth beneath them
• Building new buildings will damage the underground stability of surrounding structures
• In Texas, oil and gas extraction exacerbates settlement problems
• Climate change-induced droughts in some areas exacerbate groundwater

The researchers noted that even cities that exhibit overall stability or slightly upward movement may have problematic differential motion, while adjacent places move at different speeds or in opposite directions. This unbalanced movement can put dangerous pressure on building foundations and infrastructure.

Infrastructure is at risk

Perhaps the most worrying thing is the study’s findings on building safety. The researchers determined that there are currently about 29,000 buildings located in the area, and the land movement of the differential puts them at a high or very high risk of structural damage.

San Antonio faces the highest proportion of threatened structures, with 1 in every 45 buildings at high risk of survival-induced stress. Austin (one in 71), Fort Worth (one in 143) and Memphis (one in 167) followed closely behind.

Although a historical analysis of 225 U.S. buildings between 1989 and 2000 found that only 2% were directly attributed to settlement, the 30% factor of collapse was classified as unknown, suggesting that settlement could have had a greater role than previously recognized.

Eight most populous cities have lived on sunken lands since 2000 – New York, Chicago, Los Angeles, Phoenix, Houston, Philadelphia, San Antonio and Dallas – have experienced more than 90 major floods since 2000, which may be exacerbated by changing terrain as land production.

Going to a solution

How to solve this national challenge? The researchers stress that potential solutions vary by local conditions and specific types of settlement.

In areas with a major focus on flooding, mitigation strategies may include raising land, strengthening drainage systems and green infrastructure such as artificial wetlands to absorb flooding. For areas experiencing differential movement and tilt hazards, remodeling existing structures, implementing stricter building regulations and limiting new buildings in high-risk areas may be effective.

The researchers believe cities should use these new details to target specific solutions rather than adopting all methods of a certain size.

“With just saying that this is a question we can answer, solve, mitigate, adapt,” Ohhenhen said. “We have to turn to solutions.”

As climate change could exacerbate drought in many regions, population growth continues to increase water demand, experts warn that if no intervention, the decline rate could accelerate in the coming decades. The study provides valuable data for urban planners and policy makers to identify vulnerable areas and identify infrastructure protection before critical thresholds are reached.