U.S. cities are sinking. Here's what that means for homeowners

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

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.

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Standard homeowners insurance usually does not cover land subsidence issues, according to Policygenius, although in some areas, you may be able to purchase specific coverage for subsidence caused by nearby mines or mining activity.

Consumers are likely to see the effect of land subsidence directly, in the form of problems with their home, and indirectly, in the form of issues for their local economy.

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.

Manoochehr Shirzaei, a professor of geophysics and remote sensing at Virginia Tech, also attributed some land subsidence to tectonic processes.

"For example, earthquakes can make the land rise, but