A building collapsed in Guangxi. Photo: Getty Images
According to research published on April 19 in the journal Science, nearly half of China’s urban areas, accounting for 29% of the country’s population, are sinking at a rate of more than 3 mm per year. This equates to 270 million people living on sinking land, of which 67 million are living on land that is sinking faster than 10 mm per year.
Researchers say China’s widespread groundwater exploitation is one of the main factors causing subsidence. Cities have been pumping water from underground aquifers faster than it can replenish them, a situation exacerbated as climate change causes more severe droughts. Over-exploitation lowers the water table and causes the land above to sink.
In addition, land is also sinking due to the increasing weight of cities. Soil can become naturally compacted by the weight of sediment that accumulates over time and from heavy tall buildings pressing down on the ground, causing the soil to continuously sink.
Land subsidence is not just a problem in China. In the US, dozens of coastal cities, including New York City, are sinking. In the Netherlands, 25% of the land has sunk below sea level. And Mexico is probably the fastest sinking city in the world, with land sinking at a rate of up to 50 centimeters per year.
The impact of subsidence is often expected to be more severe along the coast, where sea levels are also rising at the same time. This combination causes more land, people and property to be affected by devastating floods.
Research shows that about a quarter of China’s coastline will be below sea level due to subsidence and rising sea levels, causing the area to suffer enormous damage and putting people’s lives at risk. Research shows that Tianjin, Shanghai and areas around Guangzhou are significantly affected by both of these problems.
A large hole appeared on the road in Zhengzhou, Henan due to subsidence. Photo: Getty Images
However, some coastal areas in China have built physical protection against the increased risk of flooding, and this study does not take those protections into account. In Shanghai, for example, Shengli Tao, study co-author and professor at Peking University, said the city has built an impressive dike system several meters high.
“Such massive coastal dike systems would largely reduce the risk of flooding even as land subsides and sea levels rise. I don’t know of any other country that has built one,” said Shengli Tao. Such a huge dyke system or not?
“Most urban cities are experiencing land subsidence, but we’re focusing our attention on coastal cities because of rising sea levels,” said Leonard Ohenhen, a doctoral student at Virginia Tech. , most urban cities experience land subsidence at levels comparable to or even greater than those in coastal cities”.
The Chinese government is addressing the problem of subsidence and sinking in a number of ways, Shengli Tao added, including enforcing strict laws to control groundwater pumping over the past few years. Shanghai and surrounding areas have restricted groundwater extraction, which has slowed the area’s rate of subsidence. He said that decades ago, subsidence in Shanghai was a very serious problem.
China has also pumped water from the Yangtze River in the south to northern China, including Beijing, which is suffering from water shortages. Research shows that the project to prevent excessive groundwater pumping has stopped land subsidence in Beijing.
“I believe that the Chinese government’s efforts will solve the problem of land subsidence. But I suggest continuing to control groundwater exploitation in large cities and continuously maintain the dyke system in coastal lands”, Mr. Shengli Tao emphasized.
