Cities are not prepared for a significant share of sea-level rise: They are drowning, too

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Fighting rising seas without reducing humanity's carbon emissions is like trying to empty the bathtub without turning off the tap. But increasingly, scientists are sounding the alarm on another problem escalating the crisis for coastal cities: their land is also sinking, a phenomenon known as subsidence. The metaphorical faucet is still on – as rapidly rising temperatures turn more and more polar ice into sea water – and at the same time the tub is sinking into the floor.

A shocking new study in the journal Nature It shows how bad the problem can be in 32 coastal cities across the United States. Previous estimates have been studied Earth centered Sea level rise, or how much the sea is rising along a given coastline. This new research believes Relative Sea-level rise, which also includes vertical movement of land. This is possible because of new data from satellites that can measure changes in elevation along the coastline at a very fine scale.

Taking that landslide into account, the study suggests that those coastal areas of the US could flood an additional 500 to 700 square miles of land by 2050, affecting an additional 176,000 to 518,000 people and up to $100 billion in property damage. There will be a loss of Rs. That's on top of baseline estimates of damage so far in 2020, which affected 530 to 790 square miles and 525,000 to 634,000 people, and cost between $100 billion and $123 billion.

Overall, the study shows that 24 of the 32 coastal cities studied are losing more than 2 millimeters per year. (One millimeter is equal to 0.04 inches.) “The combination of both land sinking and sea rise has this mixed effect of exposure on people,” says the study's lead author, Leonard Ohnhein, an environmental protection expert at Virginia Tech. ” “When you combine the two, your risk is even greater.”

The point is that cities are preparing for geocentric sea-level rise projections, for example with sea walls. Through no fault of their own—given the rudimentary state of satellite landslide monitoring—they are missing half the problem. “All the adaptation strategies we have right now are based on rising sea levels,” says Manouchehr Shirzaei, an environmental security expert at Virginia Tech and co-author of the paper. “This means that most – if not all – of those adaptation strategies are underestimating the time we have for those extreme consequences of sea level rise. Instead of 40 years to prepare, “In some cases we only have 10.”

Subsidence can occur naturally, for example when loose sediments are deposited over time, or due to human activity, such as when cities extract too much groundwater and their aquifers collapse like empty water bottles. In extreme cases, this can result in subsidence of dozens of feet. The sheer weight of coastal cities like New York is also putting pressure on land, threatening even more sinking.

Maps and graphs showing rise in water levels

Courtesy of Leonard Ohnhein, Virginia Tech