Cities are sinking and that makes them more vulnerable to climate change

America’s coastal cities are sinking, putting more people at risk of flooding than city planners expected from sea level rise alone.

The gradual sinking of land, also known as land subsidence, could lead to flooding reaching many more communities than previously expected, according to new research published today in the journal. Nature. The study looked at 32 major cities along the US coastline and predicted future flooding due to climate change. In the worst case scenario, without adequate flood defenses, up to one in 50 people and one in 35 properties in these cities could experience flooding during high tides by 2050.

Cities must prepare for the double blow, the researchers claim. The problem is twofold – sinking cities and rising seas – so the solutions must also be twofold.

“It’s something that’s not that far away.”

“It’s something that’s not that far away. And the dangers we pose are very real,” said Leonard Ohenhen, lead author of the study and doctoral candidate at Virginia Tech. “We really hope that citizens and policy makers alike, every stakeholder in the community discussion, can start thinking about how we will respond to these future changes.”

Ohenhen and his co-authors used radar satellite measurements to map land subsidence along American coasts. This allowed them to see how land is changing over time, and then predict how many more cities could sink in the coming decades. From there, they were able to model the likely extent of future flooding more accurately than predictions that do not take land subsidence into account.

“This represents a large new data set that will hopefully be useful to these communities as they plan their responses to this coming sea level rise,” said Eric Lindsey, an assistant professor at the University of New Mexico who has studied land subsidence and sea level rise. was not involved in this new article.

The study’s flood forecast is likely conservative. High water is taken into account, but flooding from groundwater is not taken into account as sinking land gets closer to the water table. “It’s like you’re sinking to the bottom of a bowl and suddenly the water around your ankles starts to rise,” says Kristina Hill, program director of the Institute of Urban and Regional Development at the University of California, Berkeley, who was not involved in the research. the study.

Some causes of land subsidence are natural, but others are man-made – meaning steps can be taken to prevent the problem from worsening. For example, by pumping water, oil and gas out of the ground, land sinks. Stop drilling and pumping, and the sinking slows down.

You can even undo some of the damage by replenishing aquifers. “The solutions to the problem of land subsidence are available in our toolbox and are very effective in a short time frame,” said Manoochehr Shirzaei, another author of the study and director of Virginia Tech’s Earth Observation and Innovation Lab.

Because greenhouse gas emissions from fossil fuels cause climate change, leaving fossil fuels in the ground is also a solution to sea level rise. Sea walls and dikes will not be enough. Even with current defenses, an additional 1,389 square kilometers of land along U.S. coasts could be threatened by sea level rise by 2050.

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