Introduction to the Study
A recent study published in Nature Cities, conducted by researchers from Columbia Climate School, examines the vertical movements of the Earth’s surface using satellite data. The study reveals that major cities in the United States are sinking at varying rates due to factors such as groundwater extraction, geological processes, and the weight of buildings.
Extent of Sinking in Major Cities
According to the study, two-thirds or more of the surface area in 25 out of the 28 most populous cities is sinking. This affects approximately 34 million people living in these areas.
Cities Experiencing the Most Sinking
- Houston, Texas
- Fort Worth and Dallas, Texas
- New York City
- Las Vegas
- Washington D.C.
- San Francisco
Causes of Sinking
The researchers determined that groundwater extraction for human use accounts for 80% of the overall sinking. In Texas, the issue is exacerbated by oil and gas pumping.
Future Implications
As urban areas continue to grow, more cities will expand into regions that are sinking. The ongoing population growth and water usage, along with droughts, will likely worsen the situation in the future.
Natural Factors Contributing to Sinking
In some areas, natural forces contribute to the sinking phenomenon. The weight of ice sheets that once occupied much of North America until about 20,000 years ago caused the land to bulge at the edges. These protuberances gradually decrease by a few millimeters each year.
Differential Movement and Its Impact
The study found that some cities experience differential movement compared to adjacent localities, either sinking at different rates or having varying elevations. This differential movement can lead to uneven settlement, potentially causing inclination and affecting buildings and infrastructure.
Only about 1% of the total surface area of these 28 cities is within zones where differential movement could impact buildings, roads, railways, and other structures. However, these areas tend to be dense urban cores containing around 29,000 buildings.
