Researchers from the Columbia Climate School’s Lamont-Doherty Earth Observatory published their study that focused on the 28 most populous cities across the country, each home to more than 600,000 Americans. Recent satellite data was used to monitor land movement down to the millimeter.
In a staggering twist, the study’s authors found that in 25 of the cities, two-thirds or more of their land was sinking. All of the 28 cities experienced some degree of land subsidence.
One city had sunk lower than any other: Houston.
According to the study, approximately 40 percent of Houston’s area subsided more than five millimeters per year, and about 12 percent was sinking at double that rate. Some localized spots were found to be sinking as much as 50 millimeters per year.
Factors such as groundwater pumping and oil extraction are causing land to cave in on itself, which poses an infrastructure risk in major urban areas. Researchers noted that buildings can be “silently” compromised over time, with damage only potentially noticeable when it is “catastrophic. "
“Unlike flood-related subsidence hazards, where risks manifest only when high rates of subsidence lower the land elevation below a critical threshold, subsidence-induced infrastructure damage can occur even with minor changes in land motion,” the study’s authors write.
The study said that the extraction of groundwater is likely the cause of subsidence in Houston, the worst-impacted city. As cities continue to expand, populations increase, and climate change worsens, areas are likely to continue sinking. Droughts, for example, can dry out soil in cities like Houston, leading to further groundwater extraction, continuing the cycle.
