Shanghai Faces Severe Flood Risk as City Sinks Amid Fastest Sea Level Rise in 4,000 Years

Dual Threat: Unprecedented Sea Level Rise and Land Subsidence

A new international study has issued a stark warning regarding Shanghai's vulnerability to severe flooding. The research, published in the journal Nature, highlights a critical combination of factors: global sea levels rising at an unprecedented rate—the fastest in at least 4,000 years—and ongoing land subsidence in the city. This dual threat places China's vital financial hub and global supply chains at significant risk.

The study, conducted by researchers from the United Kingdom, China, and the United States, found that since 1900, the average global sea level has increased by approximately 1.5 millimeters per year. This acceleration is primarily attributed to the thermal expansion of warming oceans and the melting of ice sheets and glaciers.

Shanghai's Sinking Foundation

Shanghai, situated in the low-lying Yangtze River Delta, has a long history of land subsidence, with initial records dating back to 1921. The city's foundation, built on thick, soft sediments, makes it naturally prone to sinking. However, human activities have significantly exacerbated this process.

During the 1960s, excessive groundwater extraction peaked at 200 million tonnes annually, causing parts of the city to sink by as much as 105 millimeters per year. Over the past century, some areas of Shanghai have subsided by more than one meter due to this intensive groundwater use. According to the study, approximately 94% of modern urban subsidence is linked to human activities.

Economic Impact and Global Supply Chain Risks

The economic consequences of this environmental challenge are substantial. China experiences average economic losses of US$1.5 billion per year due to the combined effects of rising sea levels and land subsidence. Shanghai alone incurred damages exceeding US$3 billion between 2001 and 2020.

The report emphasizes that cities like Shanghai, along with other major economic centers in China such as Shenzhen and Hong Kong, are critical manufacturing and financial hubs. Increased coastal flooding in these regions could severely disrupt global supply chains.

Mitigation Efforts and Future Projections

In response to the escalating threat, Shanghai has implemented measures to control land subsidence. These include tightening controls on groundwater extraction and, in some instances, reinjecting freshwater into underground aquifers. These efforts have reportedly stabilized the city's sinking rate.

Despite these mitigation efforts, computer modeling projects a significant increase in flood frequency. Current 10- and 100-year flood levels in Shanghai could be exceeded 3-5 times more frequently by 2050, and over 50 times more frequently by the end of the century with a 136 cm rise in relative sea level. Without timely adaptation measures, more than 4,200 square kilometers (62% of the total area) of the city could be flooded with an average inundation depth of 1.2 meters by the end of the century.