Study says, almost half of China's major cities experiencing land subsidence
- In Reports
- 06:47 PM, Apr 19, 2024
- Myind Staff
A recent study based on nationwide satellite data reveals that nearly half of China's major cities are experiencing "moderate to severe" levels of subsidence. This phenomenon poses a significant risk of flooding to millions of residents, particularly with the threat of rising sea levels.
Published in the journal Science, the study indicates that 45 percent of urban land in China is sinking at a rate exceeding three millimeters per year. Additionally, 16 percent of this land is subsiding at a rate exceeding 10 mm per year. The subsidence is attributed not only to declining water tables but also to the considerable weight of urban infrastructure.
According to a team of researchers led by Ao Zurui from the South China Normal University, China's urban population, which currently exceeds 900 million people, faces a significant threat due to subsidence. Even a small portion of sinking land in China could pose a substantial risk to urban life.
The study highlights that subsidence already costs China more than 7.5 billion yuan (US$1.04 billion) in annual losses. Furthermore, within the next century, nearly a quarter of coastal land in China could be lower than sea levels, putting hundreds of millions of people at an even greater risk of inundation.
Robert Nicholls from the Tyndall Centre for Climate Change Research at the University of East Anglia emphasised that subsidence is not confined to specific locations but is a national issue for China. He highlighted that it reflects broader global trends, indicating that similar challenges are occurring worldwide.
The northern metropolis Tianjin, with a population exceeding 15 million, emerged as one of the hardest-hit areas. In a recent incident, 3,000 residents were evacuated due to a "sudden geological disaster" attributed to water depletion and the construction of geothermal wells.
In regions with historic coal mining activity, such as many of China's old coal districts, over mining has exacerbated subsidence issues. Authorities have resorted to injecting concrete into deteriorating shafts to stabilize the land.
The problem extends beyond China. A separate study released in February highlighted that approximately 6.3 million square kilometres of land worldwide are susceptible to subsidence. Indonesia ranks among the most affected countries, with significant portions of Jakarta now below sea level.
According to Nicholls, there are lessons to be learned from Tokyo's experience. The city, which sank approximately 5 meters (16 feet) until groundwater extraction was banned in the 1970s, serves as a model for vulnerable urban areas seeking to mitigate subsidence risks.
Matt Wei, a geophysics expert at the University of Rhode Island, emphasised the necessity of taking subsidence mitigation seriously. He noted that while it may not be possible to halt all subsidence, adaptation measures such as building dykes should be considered.
A 2022 study conducted in Singapore revealed that out of the 44 major coastal cities affected by subsidence, 30 were located in Asia. According to Wei, the issue stems from urbanization, population growth, increased population density, and escalated water extraction, all contributing to exacerbating subsidence.
Image source: Times of India
Comments