US Cities Sinking? Here's What a New Study Found

A new study by researchers from Virginia Tech reveals that 28 of the most populous cities in the United States are sinking at an alarming rate between two and ten millimetres per year.

At least 20 per cent of the urban area was sinking by at least 2mm per year. These include cities like New York, Chicago, Dallas and Denver. The fastest sinking city in this study is Houston, which is subsiding faster than 10mm per year. Land subsidence might feel like it happens only in coastal areas but also threatens inland urban areas. It is a slow-moving hazard with great global consequences on the environment and socioeconomic situation.

The immediate risk of this sinking includes increased exposure to localised flooding and structural damages to architecture, roads, bridges, and pipelines, which will disrupt people's essential services and daily routines. Even a slight shift in land would significantly compromise the structural integrity of the city. According to the researchers, groundwater extraction is the main cause of this land subsidence. This method is a source for all agriculture, public supply, and even industrial processes, and it provides more than 70% of the total consumption.

This consumption and dependency on groundwater is alarming, as cities alone account for at least 12% of the total US population, around 34 million people. There are other causes of subsidence, for example, some parts of the country still experience the extraordinary see-sawing of bedrock caused by the retreat of glaciers during the tail of the Pleistocene epoch.

Additionally, in the west, cities like Portland, San Francisco, and Seattle can blame the case on the plate tectonics. In a press statement, the co-author of the study, Susanna Werth, claimed, “Sustained groundwater extraction lowers pore pressure in aquifer systems, leading to compaction of fine-grained sediments, which results in land subsidence that can be detected from satellites.”

This subsidence has been observed for many decades in the US; however, it has been increasingly relevant in urban areas. This does not mean that America is about to turn into Atlantis; rather, it is a wake-up call at the rate it’s sinking to help water resource managers, policy makers, city planners, and average house owners prepare for the sinking future.

This article is authored by Nikhila Gayatri Kalla as part of internship program with Deccan Chronicle.