Subsidence, the slow sinking of land beneath cities, is a growing crisis across the United States. A recent study published in the journal Nature Cities has shed light on the extent of this issue in the country’s most populous urban areas. Using satellite data, researchers found that in all 28 cities studied, at least 20% of the urban area is experiencing subsidence, with rates of up to 0.4 inches per year.
The primary cause of subsidence in these cities is groundwater withdrawal, accounting for 80% of the total subsidence. As cities expand and demand for water increases, the depletion of aquifers accelerates the sinking process. Nearly 7,000 square miles of land across the 28 cities are sinking, posing a threat to 29,000 buildings and potentially impacting 34 million people. Hotspots include major cities like Los Angeles, Las Vegas, San Francisco, and Washington D.C.
Houston has been identified as the fastest-sinking city in the United States, with 40% of its area sinking more than a fifth of an inch annually. Decades of excessive groundwater pumping and fossil fuel extraction have contributed to significant land subsidence in the city. This subsidence exacerbates Houston’s existing flooding problems, making it more vulnerable to extreme weather events.
Differential subsidence, where different parts of a building sink at varying rates, poses a significant risk to infrastructure stability. Over time, even small rates of subsidence can add up, leading to substantial elevation loss in urban areas. In some regions, such as California’s agricultural areas and Mexico City, subsidence has reached alarming levels, with land sinking by several feet or inches annually.
Roads, airports, and critical infrastructure are also at risk due to subsidence, as differential sinking can destabilize these structures. The study highlights the need for cities to address this issue by implementing managed aquifer recharge strategies to replenish depleted groundwater reserves and mitigate subsidence. By replenishing aquifers, cities can prevent further land sinking and protect their infrastructure from the effects of subsidence. Land subsidence, the gradual sinking of the Earth’s surface, is a growing concern due to groundwater mismanagement. However, according to Amanda Fencl, director of climate science for the Union of Concerned Scientists, this problem can be addressed and reversed over time.
Fencl explains that land subsidence can be reversed through natural processes like rainfall that infiltrates and recharges the groundwater, or through managed aquifer recharge. While she wasn’t involved in the research, Fencl highlights the importance of implementing sustainable practices to mitigate the effects of subsidence.
Shirzaei, a researcher involved in the study, emphasizes that in most cases, there is plenty of time to address land subsidence and that cost-effective solutions are available. By managing groundwater supplies more effectively, we can prevent further sinking of the land and protect vital resources for future generations.
Overall, the key takeaway is that land subsidence is a solvable problem that requires proactive measures and collaboration between stakeholders. With the right strategies in place, we can ensure the long-term sustainability of our water resources and prevent irreversible damage to the environment.
