Due to sinking land and rising sea levels, 32 coastal cities across the US are experiencing subsidence and have a higher risk of worsening floods. These cities include New York, Miami, New Orleans, and San Francisco.

32 Sinking US Cities

According to a new study, over half a million people in 32 US coastal cities will be threatened with repeated flooding due to rising sea levels and sinking ground. If no efforts are exerted for risk mitigation, this could lead to $107 billion worth of damages in 2050.

Roughly 30% of the population of the US lives in coastal cities, where sea levels are projected to go up by one foot in 2050. Though this was taken into account in previous forecasts, the alarming sinking rate of US cities was not factored in.

The new study "Disappearing cities on US coasts" models the blows of both sinking land and rising sea levels.

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Subsidence and Rising Sea Levels

Geophysicist Leonard Ohenhen from Virginia Tech shares that omitting subsidence in earlier estimates can be widely due to its gradual nature, which may often escape immediate attention. While the findings of the research were quite anticipated given current knowledge regarding subsidence, they were still striking.

Glaciers have been melting and ocean water has been heating due to climate change. This leads to the expansion of water and prompts the rise of sea levels, amounting to 3.4 millimeters per year in the past 30 years.

At the same time, coastal land areas are also sinking due to a mix of different factors. This includes the growing height and weight of metropolises, the downward shift of coastal land following the last ice age, and the lifting of water, gas, and other materials from the ground.

This has led to the sinking of coastal cities at a rate of five millimeters a year.

To shed more light on the threats brought about by relative rises in sea levels, the researchers fed flood hazard models with radar-obtained and precise data that charts subsidence across 32 US cities in the Gulf, Pacific, and Atlantic coasts. The models then mapped the areas with the highest risk.

Through the overlay of the flood map with 2010 US Census population data, the scientists were able to have rough estimates regarding the economic and human costs that future flooding would cost.

The scientists found that one in 50 people will end up affected if no preventive measures are taken. Low-income and minority groups would also face a disproportionate share of damages.

For these consequences to be avoided, it will be necessary for the US to limit natural gas and groundwater extraction in order to prevent further subsidence.

Ohenhen explains that it is clear that subsidence management strategies and structural defenses are both crucial. The geophysicist adds that the investments' economic implications should be factored against the possible costs of inaction, which could lead to greater social and economic impacts.

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