There are cities sinking in China. Really. As in New York and other big cities, it is observed that some cities in China are starting to collapse, and it is estimated that something will change if the situation does not change even if precautions are taken. It affects millions of people. Besides the weight of cities, we also need to talk about climate change and rising sea levels.

Now realizing this is the first brick in creating a solution.

Big cities are in danger. Although it’s something that has emerged in recent years, the latest alarm comes from a study published in the journal Science that analyzed the sleep of 82 major cities in China. Radar systems that can detect very small changes on a millimeter scale were used to measure this, and it was observed that around 40% of urban land suffers from subsidence, which is considered “moderate to severe”. Over-urbanization, the weight of buildings and our own actions are responsible for this.

Limit: year 2120. The researchers used interferometry techniques on a spacecraft-mounted radar to take measurements of China’s major cities (those with populations over two million) between 2015 and 2022. Essentially, they measured changes in the distance between the satellite and the Earth, but also how the elevations of these cities changed over the time period in question. What they discovered was that 45% of urban land was sinking at a rate of about three millimeters per year, while 16% of the cities studied were sinking at a rate of about 10 millimeters or more per year, but 5% of the cities measured had areas that were subducted at a rate of about three millimeters per year. here the subsidence is just over two centimeters per year.

These important cities include Shanghai as well as Beijing or Tianjin. In fact, Beijing’s situation appears critical, as areas near some areas, such as highways, are estimated to be subsiding at 45 millimeters per year. And by 2120, they say, 22 percent to 26 percent of China’s coastal land will have a relative elevation below sea level. This represents 9 percent to 11 percent of the country’s coastal population, and to give context, Shanghai has sunk three meters in the last century.

It’s our fault. No matter how much the buildings weigh, if their foundations are solid, why do cities sink? Even though these foundations were laid properly, it turned out that the sinking of the cities was due to the withdrawal of groundwater. The analysis revealed that the fastest sinking areas corresponded to places where more than 1,600 water extraction wells were registered.

When water recedes and natural resources cannot be replenished sufficiently, sedimentary basins consisting of soft soil that must bear the weight of the city are formed. This process of soil settling is called subsidence, and it’s something we can speed up through our actions. It’s visible in some cities, but it’s not the only thing affecting the future of major coastal cities.

Solutions? Discovering that this is happening is the first step in trying to find a solution. Other major Asian cities affected by this process are Osaka and Tokyo. But they began to find a solution a few decades ago, by stopping the extraction of groundwater in 1970. As a result, the subsidence was significantly reduced and stopped at some points.

The problem is that China is urbanizing at a rapid pace, and not only is the construction of increasingly vertical cities instead of horizontal ones accelerating the process, but traffic itself is a key element in this collapse, due to the vibration of millions of vehicles passing by. roads. This explains why some of Beijing’s most subsidence-prone areas are located around highways or subways. Another solution would be to put up barriers that would stop the sea when cities are in trouble, something cities like New York have already tried.

This doesn’t just affect China. This collapse is observed in some cities, but it is not the only thing affecting the future of large coastal cities. Robert Nicholls is a climate change researcher at the University of East Anglia, and although he was not involved in the research, he says “we need to learn from this experience to solve the problem because it is more widespread than is currently known.”

For example, in the United States, subsidence problems occurred in thousands of square kilometers in 45 different states. break and exploitation of groundwater, activities responsible for more than 80% of identified sinkings.

Currently, resolving the problems caused by this sinking costs China approximately $1.05 billion a year.

Image | Fanghong

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