On 18 April, Science Journal published a study that says China’s major cities lost more than 10 millimetres of elevation per year; half of the cities are losing more than 3mm yearly. Despite minor changes, their accumulation over 100 years will threaten one-fourth of China’s coastal cities below the sea level. The study used a spaceborne synthetic aperture radar interferometry technique to assess land subsidence in China’s major cities from 2015 to 2022.

What is Land Subsidence?
According to the National Oceanic and Atmospheric Administration (NOAA), “land Subsidence is a gradual setting or sudden sinking of the Earth’s surface.” It can happen naturally, such as earthquakes, soil compaction, glacial isostatic adjustment, erosion, sinkhole formation, and human activities, such as removing water, oil, natural gas, or mineral resources from the ground by pumping, fracking, or mining.  Land subsidence is an overlooked problem that is not just limited to China but around the world.

The following are the four takeaways of the above report on the issue.

1. Land subsidence across China is pervasive
Major cities like Beijing, Tianjin, and Shanghai witnessed land subsidence as early as the 1920s. China currently witnesses widespread evidence of land subsidence issues in 82 cities. As the study says, around 16 per cent of urban land is sinking more than 10mm a year, greater than the rest of the world. This would impact the 67 million people who are residing in these areas. Also, more than 44.7 per cent of the 82 cities are shrinking faster than 3mm a year.

In China’s Northeastern region, especially in the Daqing province, the lands are shrinking by 22mm. This has become critical as they have been comprised of industrial hubs established since the 1950s. The lands in the Central-Northern region of China close to Beijing and Tianjin are sinking by 52mm a year. This becomes critical as the region’s population density and groundwater demand are very high.

The lands in the Central China region containing many renowned industrial cities such as Pingdingshan, Jincheng, and Huainan are sinking by 28mm/year, 23mm/year, and 17mm/year, respectively. The lands in the Southern China region comprising provincial capital cities such as Kunming, Nanjing, and Guiyang are sinking by 15mm/year, 18mm/year, and 14mm/year. The lands in Southeastern China comprising coastal cities such as Wenzhou and Shantou are sinking by 34mm/year and 21mm, respectively.

2. Weight of the buildings, groundwater loss, and land reclamation activities are major reasons
First, the weight of the buildings. China’s rapid economic boom coincides with urbanization. The urban population share has risen from 13 per cent in 1950 to 60 in 2021. Urbanization demands large-scale construction of buildings to accommodate a high-density population in limited spaces within the cities. The weight of the buildings imposes huge geostatic pressure on the urban subsurface, especially the bedrock and the earth’s crust. This can have a significant impact within a few years of construction. This was evident in major cities such as Beijing and Shanghai, which impacted the cities' economic prospects.

Second, the groundwater loss. The groundwater loss due to increased urbanization for drinking, construction, and agricultural practices has severely impacted the water table across major Chinese cities. Experts indicated that China’s excessive pumping of water from its natural aquifers underground has led to the collapse of rock formations, thereby impacting the surface buildings. The study found that anthropogenic activities had led to severe land subsidence in Chinese cities. This was evident in the groundwater changes in Northern China due to the government’s policies, such as the South-North Water Diversion Project, which has led to the transfer of water from the Yangtze River to northern cities. These actions destabilized groundwater and increased land subsidence, as found in cities like Beijing and Tianjin. This shows how major infrastructure projects built without proper study of sustainable impact on the environment can cause severe disasters in the future.

Third, increased land reclamation activities in coastal areas. Since the early 2000s, land reclamation activities have been meant to alleviate the shortage of coastal land amid rapid urban and economic growth. According to the study, provinces such as Zhejiang, Guangxi, Taiwan, Hong Kong, and Macao constituted more than 50 per cent of China's coastal land reclamation activities. This is due to socio-economic factors such as agricultural land shortage, development of coastal industry, increased urbanization, population growth, and economic development.

3. Land subsidence will affect real estate, infrastructure and drinking water
The issue of land subsidence is slowly impacting the country’s economy, which is facing severe issues such as the real estate sector crisis, mounting local and provincial debts, high-interest rates, etc. The land subsidence will hurt the pace of planned infrastructure projects in China, which are set to aid the country’s target of 5 per cent economic growth in 2024. Also, the rising sea levels by 0.87 meters yearly will impact the durability of the existing urban infrastructure, making it prone to disasters such as flooding and earthquakes.

Excessive use of groundwater for construction and agricultural purposes has created drinking water shortages across major Chinese cities. Water pollution has resulted in severe economic and social costs, as China has spent more than USD 200 billion on water clean-up projects. Due to this, nine northern provinces in China face absolute water scarcity.

4. Land subsidence will lead to migration
China’s rapid urbanization has saturated the living spaces in many urban cities due to its huge economic value, such as employment opportunities. More than 90 per cent of the Chinese population and 60 per cent of the industrial capacity on the eastern side are vulnerable to rising sea levels. Even if the government aims to urbanize the interior parts or western parts, it may be difficult as the terrain does not support the construction of megacities. If China’s urbanization grows rapidly, it is estimated that by 2070, the Chinese economy will face a major economic crisis.

References:
Delger Erdenesanaa, “China’s Cities Are Sinking Below Sea Level, Study Finds,” The New York Times, 18 April 2024
Zurui Ao, et. al., “A national-scale assessment of land subsidence in China’s major cities,” Science, Vol 384, pg 301-306, 18 April 2024
Matt McGrath, “Water extraction and weight of buildings see half of China's cities sink,” BBC, 19 April 2024
David Stanway, “Nearly half of China's major cities are sinking, researchers say,” Reuters, 19 April 2024
Michele Lancia, et. al, “The China groundwater crisis: A mechanistic analysis with implications for global sustainability,” Elsevier, Vol 4, October 2022
“What is subsidence?,” National Oceanic and Atmospheric Administration, 24 August 2023