China’s multi-million dollar cities are sinking

China’s multi-million dollar cities are sinking

Published 21.04.2024 | By Йосиф

China’s multi-million dollar cities are sinking

Almost half of China’s major cities are sinking because of water extraction and the increasing weight of their rapid growth, researchers say.

Some cities are sinking fast, with one in six sinking at more than 10mm a year.

China’s rapid urbanization in recent decades means that much more water is now being extracted for human needs, scientists say. In coastal cities, this subsidence threatens millions of people with flooding as sea levels rise.

China has a long history of dealing with landslides, with both Shanghai and Tianjin having records of subsidence dating back to the 1920s. Shanghai has sunk by over 3m in the last century.

In recent years, the country has seen widespread evidence of subsidence in many of the cities that have grown rapidly in recent decades.

To understand the scale of the problem, a team of researchers from several Chinese universities studied 82 cities, including all cities in the country with a population of more than 2 million people. They used data from the Sentinel-1 satellites to measure vertical ground motions across the country.

For the period from 2015 to 2022, the team was able to establish that 45% of urbanized areas are sliding at more than 3 mm per year. About 16% of urban land is subsiding faster than 10 mm per year, which scientists define as rapid subsidence. This means that 67 million people live in rapidly sinking areas.

The researchers say that the cities that face the most serious problems are concentrated in the five regions of the map:

Subsidence is affected by a number of factors, including geology and the weight of buildings, but the most serious effect on the processes is the loss of groundwater. This means extracting these waters for the needs of the local population – a process that has already been observed in other highly populated regions of the world, incl. Houston, Mexico City and Delhi.

In China, the research team was able to make the connection between water withdrawals from over 1,600 monitoring wells and increasing rates of land subsidence.

Other factors that influence landslides are local transportation systems and mining of minerals and coal. In the northern Pindingshan region, one of the largest coal regions in the country, the land is sliding at an extremely fast rate – about 109 mm per year.

The authors of the study say that the big threat going forward is putting populations at risk of flooding caused by the combination of landslides and sea level rise, which in turn is affected by climate change.

In 2020, about 6% of China’s land area was below sea level. In 100 years, this percentage could rise to 26%.

Researchers say land is sinking faster than sea levels are rising, but these two factors will put hundreds of millions of people at risk of flooding.

Land subsidence problems have also affected other major urban centers in Asia, including Osaka and Tokyo in Japan in 2010.

Fortunately, research shows that there are effective strategies that can combat the slow decline in area.

The research was published in the journal Science.

https://novini.bg/sviat/analizi/841131