A comprehensive study based on nationwide satellite data has unveiled a concerning reality: nearly half of China’s major cities are experiencing “moderate to severe” levels of subsidence, posing a significant risk of flooding, particularly in the face of rising sea levels. Published in the journal Science, the research sheds light on the extensive land sinking phenomenon, driven by both declining water tables and the weight of urban infrastructure.
The study’s authors, led by Ao Zurui from South China Normal University, highlight the gravity of the situation, emphasizing that over 45% of China’s urban land is subsiding faster than 3 millimeters per year, with a staggering 16% experiencing rates exceeding 10 mm per year. With China’s urban population surpassing 900 million, the implications are profound, potentially endangering millions of lives.
Subsidence already inflicts significant economic losses, surpassing 7.5 billion yuan annually. Moreover, projections suggest that within the next century, nearly a quarter of coastal land could sink below sea levels, amplifying the risk of inundation for hundreds of millions of people.
The city of Tianjin, with a population exceeding 15 million, stands out as one of the worst-hit areas. Last year’s evacuation of 3,000 residents following a “sudden geological disaster” underscored the severity of the issue, attributed to water depletion and geothermal well construction.
China’s historical coal districts have also borne the brunt of subsidence, exacerbated by overmining, prompting interventions such as injecting concrete into collapsing shafts. However, the problem extends beyond China, with global implications highlighted by a separate study revealing over 6.3 million square kilometers of at-risk land worldwide.
Lessons from Tokyo’s successful mitigation efforts, which included banning groundwater extraction, offer valuable insights for vulnerable cities. However, with 44 major coastal cities grappling with subsidence, urgent adaptation measures, including building dykes, are imperative.
As urbanization and population growth escalate, addressing subsidence emerges as a pressing global challenge requiring concerted efforts in mitigation and adaptation strategies. With Asia bearing the brunt of this phenomenon, collaborative action is essential to safeguarding vulnerable populations and securing the resilience of coastal cities worldwide.
