Houston: The fastest-sinking city in the U.S.

A recently published study found that Houston (Texas) is the fastest-sinking major city in the United States, with more than 40% of its land area subsiding faster than five millimetres per year[1].

The study used satellite data from a period of six years to measure how fast the 20 most populous cities in the U.S. are sinking. Researchers also studied the impact that subsidence has on buildings and infrastructure.

The study found that in Houston, 42% of the area was sinking about five millimetres per year, with 12% are is sinking by as much as 5 centimetres per year.

The researchers determined that groundwater removal for human use was the main cause for 80% of overall sinkage. The researchers say that continued population growth and water usage combined with climate-induced droughts in some areas will likely worsen subsidence in the future. The problem is compounded by oil and gas extraction around Houston.

This subsidence is caused by the settling of the ground into the voids left behind after water or oil is removed.

When a land area subsides, it can make the region more prone to flooding, and lead-author Ohenhen said previous research has suggested that subsidence exacerbated the flooding seen during Hurricane Harvey in 2017.

"Subsidence lowers the ground surface, allowing water to collect within a specific region of the city," he said. "You often have drainage which will allow water to flow from one direction to the other. When you change that, you basically stop the water from moving through the pathway it would normally take, and it goes into other areas [and] allows water to remain in an area for an extended period of time."

The perpetual shifting of the ground can also lead to damaged buildings and uneven roads, Ohenhen explained. While the simplest solution would be to stop extracting water and oil from the ground to prevent the further acceleration of subsidence, Ohenhen said that is not always feasible.

This is the America where most of the damage of hurricane Katrina from late August 2005 still hasn't been repaired.

[1] Ohenhen et al: Land subsidence risk to infrastructure in US metropolises in Nature Cities - 2025