Shanghai Faces Rising Seas and Land Subsidence Crisis, Study Finds

2024.04.19 Fri Posted at 18:47 JST

(CNN) According to a study published in the US academic journal Science on the 18th, almost half of China’s urban areas, where 270 million people, or 29% of the country’s population, are sinking at least 3 millimeters in the year.

67 million people live on land that is sinking more than 10 mm per year.

Researchers say that extensive groundwater pumping in China is one of the main reasons for land subsidence. Cities pump water from underground aquifers at a faster rate than the ground water can collect. This situation is getting worse due to drought caused by climate change. Excessive pumping lowers the groundwater table and causes the overlying ground to sink.

Land also sinks due to the increased pressure of the city itself. Due to the pressure of the earth and sand that has accumulated over many years and pushing down heavy buildings, the soil is naturally compacted and gradually sinks.

Land subsidy is not just a problem in China. Dozens of coastal cities in the United States, including New York City, are sinking. In the Netherlands, 25% of the country has sunk and is now below sea level. It is believed that Mexico City is experiencing the fastest land subsidence in the world, with land sinking up to 50 centimeters per year.

On the coast, the impact of land subsidence is more severe and sea levels are rising, subjecting more land, people and buildings to destructive floods.

The study suggests that around a quarter of China’s coastline will be below sea level due to land subsidence and an expected rise in sea level, causing significant damage and endangering human life. The areas around Tianjin, Shanghai, and Guangzhou are exposed to both of these problems.

Embankments have already been built in some coastal areas of China to physically protect areas from increased flood risk. Researchers say that the city of Shanghai, for example, has built embankments several meters high.

“A large coastal levee system like this greatly reduces the risk of flooding, even considering both land subsidence and sea level rise,” the researchers told CNN that I don’t know of any country another.

He said the Chinese government has used several methods to combat land degradation in recent years, including enforcing strict laws governing groundwater pumping. In Shanghai and surrounding areas, the rate of land subsidence has been slowed by limiting groundwater pumping.