Ground Beneath Their Feet: China's Sinking Cities And Rising Seas

Millions in China are finding the ground beneath their homes sinking due to human activities, putting coastal regions at greater risk of flooding and sea level rise, according to new research.

A study published in the journal Science reveals that nearly half of China’s urban areas, home to 29% of the population, are subsiding at a rate exceeding 3 millimeters (about 0.12 inches) per year. That equates to 270 million people residing on sinking land, with 67 million experiencing even faster subsidence of over 10 millimeters (0.4 inches) annually.

The primary culprit behind this phenomenon is the excessive extraction of groundwater, exacerbating by climate-induced droughts. As cities pump water from underground aquifers faster than they can be replenished, the water table drops, causing the land above to sink. Additionally, the sheer weight of urban infrastructure contributes to this sinking, as heavy buildings compress the soil over time.

This problem isn’t exclusive to China. In the US, cities like New York are facing similar challenges, while in the Netherlands, a quarter of the land has sunk below sea level. Mexico City holds the title for the world’s fastest-subsiding city, sinking at a staggering rate of nearly 20 inches per year.

Coastal regions bear the brunt of this sinking, compounded by rising sea levels. As land subsides, it exposes more areas to destructive flooding, endangering lives and property. The study predicts that a quarter of China’s coastlines will be below sea level due to subsidence and projected sea level rise, particularly affecting cities like Tianjin, Shanghai, and Guangzhou.

However, some coastal areas have implemented protective measures. Shanghai, for instance, boasts impressive dike systems that mitigate the risk of inundation. Yet, the study warns that these protections are not comprehensive.

While coastal cities often receive attention for sinking, urban areas worldwide face similar challenges. Leonard Ohenhen, a researcher at Virginia Tech, notes that urban land subsidence is widespread, with rates often surpassing those of coastal cities.

The Chinese government has taken steps to address the issue, including enacting laws to regulate groundwater extraction and implementing projects to divert water from the Yangtze River to alleviate shortages. These efforts have shown promise, with subsidence rates slowing in regions like Shanghai.

However, continued vigilance is necessary. Researchers recommend ongoing control of groundwater extraction in major cities and the maintenance of coastal defense systems to safeguard against the dual threats of subsidence and rising sea levels.