Major Chinese cities are sinking

According to a new study, 270 million people live on sinking land

a Land Millions of people in China's major cities are submerged underfoot due to human activities, putting the country's coastal areas at greater risk of flooding and rising sea levels, according to new research.

Nearly half of China's urban areas, covering 29% of the country's population, are sinking at a rate of more than 3 mm annually, according to the study published Thursday in the journal Science Magazine. There are 270 million people living on sinking land.

Meanwhile, 67 million people live on land that is sinking rapidly, at a rate of about 10 millimeters per year.

Large-scale groundwater extraction in China is one of the main factors behind the decline, according to researchers. Cities are pumping water from aquifers faster than it can be replenished, a situation exacerbated by drought caused by climate change. Overpumping lowers the water table and weakens the ground it covers.

The land is also sinking due to the increasing weight of the cities themselves. Soil can naturally become compacted due to the weight of sediments that accumulate over time and heavy buildings pressing down on the ground, causing the ground to continually sink.

Soil sinking is not a problem limited to China. in the United States of America, Dozens of coastal citiesincluding the city New YorkThey're drowning. In the Netherlands, 25% of its land has sunk below sea level. and on Mexico CityIt is perhaps the fastest sinking city in the world, with the earth sinking at a rate of up to 50 centimeters per year.

The effect of this phenomenon is usually worse along the coasts, where sea levels rise at the same time. This combination exposes more land, people and property to devastating floods.

The study indicates that about a quarter of China's coast will be below sea level due to the expected subsidence and rise in sea level, exposing the region to serious damage and putting people's lives at risk. According to the study, Tianjin, Shanghai and the areas surrounding Guangzhou are highly vulnerable to both problems.

But some coastal areas in China have already built physical protections against the increasing risk of flooding, and the study does not take these protections into account. In Shanghai, for example, the city has built “impressive” meter-high dam systems, said Shengli Tao, a co-author of the study and a professor at Peking University.

“These massive coastal levee systems will significantly reduce the risk of flooding, even taking into account land subsidence and sea level rise,” Tao told CNN International. “I'm not aware of other countries that have built these huge dam systems.”

Leonard Ohinen, a doctoral researcher at Virginia Tech in the US, who recently published a study on subsidence, said the study was “scientifically sound” and did a “good job” in highlighting that subsidence is not just a “coastal problem.” Land in the United States of America.

“Most urban cities suffer from land subsidence, but we focused our attention on coastal cities because of sea level rise,” Ohinen, who was not involved in the study, told CNN International. “However, most urban cities are experiencing land subsidence at similar or even higher rates than coastal cities.”

Tao said the Chinese government is dealing with sinking land in several ways, including implementing strict laws to control groundwater pumping in recent years. Shanghai and its surrounding areas have been limiting groundwater extraction, slowing the rate of subsidence in the region. Decades ago, Shanghai's decline was a big problem.

China also pumps water from the Yangtze River in southern China to the north – including Beijing – which suffers from water shortages. The study concluded that the project avoids the need to pump excess groundwater and puts an end to land subsidence in Beijing.

“I believe the Chinese government's efforts will solve the land subsidence issue,” Tao said. “But I propose that groundwater extraction should continue to be controlled in major cities and that dam systems be constantly maintained in coastal areas.”