The rise of sea level rise in China’s coastal cities as a consequence of the sinking rate of seawater and its impact on buildings and infrastructure
The paper ties a number of factors to sinking, such as thedepth of a city’s bedrock, underground mining, use of transport systems and the weight of buildings.
But there are also stories of successful mitigation. Tokyo slowed its sinking from a rapid 240 mm a year in the 1960s to about 10 mm a year in the early 2000s, after passing laws that limited groundwater pumping. Shanghai, China, which sank by a staggering 2.6 metres between 1921 and 1965, reduced its annual rate of sinking to about 5 mm after implementing a series of environmental regulations.
It is a risk for cities around the world when land sinks relative to its surroundings. Sea level rise is accelerated by land being lowered as the ocean goes higher. Water trapped in sinking areas can cause drainage issues, as well as damaging buildings and roads.
A paper is published in Science today that shows that one in ten residents of coastal cities in China will be living below sea level within a century.
“This is a big problem,” says Robert Nicholls, a subsidence expert at the University of East Anglia in England who was not involved in the study. “The scale is large. It makes you realize 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. The rise of the oceans is due to pollution from burning oil, gas and coal.
In the Netherlands, one-quarter of the land has gone below sea level. And by 2040, almost one-fifth of the world’s population is projected to be living on sinking land.
In the United States, more than 44,000 square kilometres of land across 45 states has been directly affected by subsidence, with more than 80% of the cases relating to groundwater extraction, often for agricultural purposes.
After land reclamation, consolidation occurs when the soil is compressed and this causes subsidence in Macao and Hong Kong.
The weight of buildings was listed as a factor by the authors. 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.