A new study reveals extensive subsidence across China, raising serious concerns for coastal cities vulnerable to rising sea levels

A recent scientific study has highlighted a grave environmental challenge facing China—land subsidence impacting major urban centres, with potentially devastating consequences for roughly 270 million people. Published in the journal Science, the research indicates that nearly half of China’s urban land is sinking at a rate exceeding 3 millimetres per year due to human activities, particularly excessive groundwater extraction.

The situation is particularly dire for 67 million residents living in areas where the ground subsides more than 10 millimetres annually. These rates of land subsidence are concentrated in China’s bustling coastal cities, such as Shanghai, and Tianjin, and regions around Guangzhou, which are simultaneously grappling with the threats of rising sea levels.

Groundwater withdrawal has been identified as a primary cause of the subsidence. Cities across China have been extracting water from aquifers at rates faster than natural replenishment, a practice exacerbated by climate-induced droughts. This excessive pumping results in lower water tables, which in turn causes the ground above to settle or sink. Additionally, the physical weight of urban development contributes to the sinking by compacting the soil further.

The implications of these findings are far-reaching. The combination of land subsidence and sea level rise sets the stage for increased flooding, especially along China’s coasts, where about a quarter of the territories might soon lie below sea level. This scenario exposes more land, properties, and millions of people to the risk of severe flooding from coastal storms and erosion.

However, it’s not all grim news. Some regions, particularly Shanghai, have taken significant steps to mitigate these risks. According to Shengli Tao, co-author of the study and a professor at Peking University, Shanghai has constructed extensive dike systems that considerably reduce the risk of inundation, a level of preparedness not commonly seen in other nations.

Addressing the subsidence issue, the Chinese government has implemented stricter regulations on groundwater extraction in recent years. In areas like Shanghai, measures to limit water withdrawals have already slowed the rate of land sinking. Additionally, a massive infrastructural project now redirects water from the Yangtze River in the south to the parched northern regions, including Beijing, alleviating the need to overly extract groundwater and helping to halt land subsidence in the capital.

The findings from the study underscore the urgency for continued efforts to manage groundwater use effectively and to maintain and expand flood defenses, particularly in vulnerable coastal areas. These steps are vital not only for safeguarding infrastructure and economies but also for protecting the lives of millions of residents facing the dual threats of human-induced subsidence and natural sea level rise.