US cities are sinking


The land below many U.S. cities is sinking, including New Orleans, New York City, Miami and south San Francisco, CNBC reports.

US cities are sinking
This phenomenon, known as land subsidence, can severely affect the integrity of buildings and infrastructure. When coupled with a sea-level rise, it can greatly increase the incidence of flooding.

Problems associated with land subsidence can cost U.S. homeowners 6% of their home value. In areas with high subsidence, that number can jump to 8.1%, according to forthcoming research done by assistant professor of public policy Mehdi Nemati at the University of California, Riverside, and his colleagues. Their research focused on the Central Valley of California, but Nemati said the findings could be extrapolated nationwide.

Both natural and man-made processes cause land subsidence.

As glaciers are receding from the land in the U.S. and Canada, the process creates a “see-saw” effect where the land in the U.S. falls but rises in Canada, researchers say.

Human-induced land subsidence relates to how we have developed our cities, namely groundwater extraction and building practices.

“We use groundwater to drink and for other purposes. And as we take water out from the land, the space beneath it becomes compact because we’ve built on top of it,” said Rob Freudenberg, vice president of energy and environment at the Regional Plan Association. “Heavy building materials also compact the land, putting infrastructure at risk.”

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