Some of the major cities in China are sinking quickly

Urban Subsidence and Climate Change in the Twenty-Year Rise and Fall of China’s Coast Cities: A Case Study in New Orleans, China

In 2022, Wei and his colleagues found that land was sinking faster than sea levels were rising in many coastal cities worldwide. They believed that the cities would be challenged by flooding more quickly than projected by the sea-level models if they continued to sink.

In the twentieth century, parts of Tokyo have subsided by 15 feet, but have been kept from collapsing by strict groundwater rules.

Many Asian cities are built on river Deltas that are prone to sinking, and that’s where the high levels of subsidence are. New Orleans is a place that is sinking quickly in the U.S.

One in ten residents of the coastal cities of China could be living below sea level within a century if land subsidence and climate change continue, according to the paper published today.

Robert Nicholls, who was not involved in the study but is an expert on the causes of subsidence in England, says it is a big problem. “The scale is large. Without doubt, it brings home that this is not a local problem. This is a national, or even international, problem.”

That means tens of millions of people are already at risk, and that could grow to hundreds of millions if China’s cities continue to both grow in population and subside at their current rate, and seas continue to rise. Climate change due to greenhouse gas emissions from burning oil, gas and coal is leading to the rise of oceans.

A quarter of the land in the Netherlands has fallen below sea level. And by 2040, almost one-fifth of the world’s population is projected to be living on sinking land.

Over 44,000 square kilometres of land in the United States has been directly affected by subsidence with 80% of the cases related to farmland being used for agriculture.

Ding says that, in cities such as Macao and Hong Kong where no groundwater is used, subsidence mainly comes from consolidation — downward movement as a result of soil being compressed — after land reclamation.

The authors also listed the weight of buildings as a factor. Contrary to expectations, heavier buildings, such as the skyscrapers in Shanghai, tend to sink slower than lighter structures do, possibly because those buildings are anchored on deeper rock, according to the paper.