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Around 250 million people in China live in major cities facing moderate to severe subsidence, a consequence of excessive groundwater extraction and urban expansion. This poses a significant risk of flooding and other disasters. Coastal cities are particularly vulnerable due to rising sea levels from climate change, which could lead to more severe flooding and erosion, endangering infrastructure, homes, and ecosystems without immediate action.
Highlighted on a map are five rapidly sinking urban areas, including Beijing and Shanghai, with populations exceeding 21 million and 26 million, respectively. These cities are home to over 242 million people, comprising more than one-sixth of China's population. Researchers used synthetic aperture radar (SAR) imagery to monitor 82 cities, estimating that 29% of the population lives in areas subsiding at over 3 millimeters annually, while 7% reside in regions sinking more than 10 mm per year.
Without changes in subsidence rates, the proportion of land below sea level could significantly increase by 2100, leading to widespread inundation if adequate defenses are not implemented. Subsidence-related disasters have already caused hundreds of fatalities and injuries yearly, with economic losses surpassing $1 billion as of 2014, according to the China Meteorological Administration (CMA).
Subsidence-induced fissures can severely damage infrastructure, while catastrophic flooding poses a significant risk, as seen in Guangdong's recent evacuation of over 100,000 people. Mitigation and adaptation strategies are crucial, as explained by Robert Nicholls, a climate adaptation professor. He noted successful efforts in Tokyo, Osaka, and Shanghai to slow subsidence by regulating groundwater withdrawal. If mitigation fails, adaptation through improved dike systems and strategic land use is necessary, although Nicholls considers complete retreat or abandonment unlikely in China.