China's Major Cities Sinking at Alarming Rates, Study Finds

China is facing a serious land subsidence crisis, with nearly half of its major cities sinking faster than 3 millimeters per year, according to a new study by Chinese scientists. The research, which analyzed satellite data from 82 cities across China between 2015 and 2022, found that 16% of these urban areas are losing more than 10 millimeters of elevation annually.

The rapid subsidence, combined with rising sea levels, could result in one-fourth of China's urban coastal land sitting below sea level within the next 100 years, putting millions of people and billions of dollars in infrastructure at risk. The study estimates that around 270 million urban residents, nearly one-third of China's urban population, are affected by subsidence.

The primary driver of this issue is the excessive extraction of groundwater, which lowers the water table and causes the overlying land to sink. The growing weight of cities themselves, due to soil compaction and heavy buildings, is also contributing to the problem. Hotspots for subsidence include major cities like Beijing, Tianjin, and Shanghai.

Why this matters: Land subsidence is a significant national and international problem, as it can damage buildings and infrastructure, and accelerate local sea level rise. Coastal cities are particularly vulnerable, as subsidence reinforces the impacts of climate change and sea level rise, exposing more land, people, and property to destructive flooding.

The Chinese government is addressing the issue by implementing strict laws to control groundwater pumping and diverting water from the Yangtze River to northern China, which has helped stop land subsidence in Beijing. Some coastal cities like Shanghai have also built impressive dike systems to reduce the risk of inundation.

However, experts suggest that continued efforts to control groundwater withdrawals and maintain dike systems are crucial to mitigating the land subsidence crisis. "Roughly a quarter of China's coasts will be lower than sea level due to subsidence and sea level rise," said a lead researcher at Fudan University in Shanghai. "This puts lives and livelihoods at risk, and requires urgent action from policymakers and city planners."

Key Takeaways

• Nearly half of China's major cities are sinking over 3 mm/year.
• 16% of urban areas are losing over 10 mm of elevation annually.
• Excessive groundwater extraction and city weight are driving subsidence.
• 1/4 of China's coastal land may sit below sea level in 100 years.
• China is implementing laws and infrastructure to mitigate the crisis.