Excessive construction and groundwater extraction are contributing to the sinking of major cities in China, putting hundreds of millions of residents at risk of flooding and other damages.
As intense rainfall and destructive floods prompted recent evacuations in Southern China, researchers uncovered a few days ago that rapid urbanization is also exacerbating land subsidence.
Researchers from Peking University used satellite technology from a European Space Agency satellite to measure the extent of land subsidence occurring in 82 major cities in China. InSAR, the observation technique used, enabled them to find that nearly half of the urban land examined is sinking at a rapid rate.
The researchers concluded in their study that if preventative measures are not taken soon, in 100 years, a quarter of China’s land will be submerged in water, published in the journal Science on April 18.
The change in land elevation is due to a combination of factors: climate change causing rising sea levels, depletion of groundwater to provide for a growing urban population, and excessive construction of high-rise buildings.
Since April 16, sustained torrential rain in the province of Guangdong has forced more than 110,000 people to relocate, and killed at least 4 people while 10 remain missing.
Groundwater-related subsidence, which renders land more susceptible to flooding, will only exacerbate climate change-related incidences and more extreme weather phenomena. When excessive amounts of water are pumped out of the ground faster than it can be replenished, it causes land subsidence as the soil compacts, drops and may even collapse.
Jakarta is considered the fastest-sinking city in the world, with a land subsidence of 2–15 centimeters a year due to excessive water extraction.
However, due to rapid urbanization, Chinese cities are now catching up. The country is engaging in construction activity on the largest scale in the world, adding 2,000 square kilometers (772 square miles) of new building floor area per year.
As a result, 45% of the examined urban land is sinking at a rate of 3 millimeters per year, affecting 270 million people. Even more urgently, 67 million people live on land sinking at a rate of 10 millimeters per year. Some other coastal cities are experiencing subsidence of 22 millimeters annually.
These findings are worrying experts. Climate change has already made coastal cities the most susceptible to flooding and storms, and with a rapid land subsidence rate, these conditions are becoming more dangerous.
Last year, more than 3,000 people were evacuated from high-rise buildings in China’s northern city of Tianjin due to massive fissures appearing on roads. The government reported that the cracks were due to a land subsidence issue, with the city now in the top five sinking cities in the world.
The phenomenon is not new in China; Shanghai has been slowly sinking and has fallen by 3 meters in 100 years due to groundwater overuse and the weight of buildings.
A silent global problem
Cities in the United States and Europe are experiencing the worrying trend too; in New York City, land subsidence is occurring at a rate of 1–2 millimeters per year due to excessive construction.
A previous study published in Geophysical Research Letters found that 33 out of 99 examined coastal cities are sinking at a rate of more than one centimeter, which is five times faster than the rate of sea level rise. This particular study spelled out bad news for Houston, Texas. According to the report, the city is on track to being completely submerged by 2100.
The Netherlands has also been facing this problem for a while. Maarten Kleinhans, professor of geosciences and physical geography at Utrecht University, described to POLITICO a “really scary situation” in the Netherlands, where some areas of the country were already built 10 meters below sea level, and that people are trapped in a “false sense of security.” Amsterdam, for example, is sinking at a rate of 8 millimeters per year.
However, China is the first country to have such a wide range of cases.
The assessment concluded that the situation is urgent and highlights the necessity of enhancing protective measures to mitigate the potential damages from land subsidence.
China’s sponge cities
Some of China’s coastal cities have been preparing for sea level rise. The World Economic Forum reported China’s “sponge city” initiative of 2015, investing in permeable pavement, artificial ponds, wetlands, and rain gardens that store excess rainfall. By ensuring that 80% of all urban lands repurpose stormwater through this green infrastructure, around 30 cities, including Shanghai, are limiting groundwater extraction.
However, the “sponge city” initiative has been implemented unevenly, with some cities lacking the necessary legislation to reduce urban flood risks. The cities involved remain vulnerable to heavy rain, according to Reuters.
The infrastructure is only able to handle 200 millimeters of rain per day, and in 2023, heavy rainstorms overwhelmed Beijing with over 745 millimeters in three days, while Zhengzhou experienced 200 millimeters in just one hour.
Although the initiative has achieved positive effects through low-impact green projects, the recent study from Peking University shows that the majority of major cities in China, including those involved in the “sponge city” initiative such as Beijing, Shanghai, and Tianjin, do not have adequate resources to mitigate the effects of land subsidence, whether it be due to extreme weather or groundwater extraction.
