Satellite research indicates that nearly half of China’s major cities are experiencing subsidence at moderate to severe levels, putting millions of people at risk.
This study was conducted by a team of scientists from South China Normal University and was published in the prestigious journal Science on April 19.
Building density in Shanghai, China – (Photo: REUTERS).
Based on satellite data, the study authors found that 45% of Chinese cities are sinking at a rate of more than 3mm per year, with as much as 16% experiencing rates exceeding 10mm per year. This is due not only to declining groundwater levels but also to the weight of buildings above ground, according to AFP.
With China’s urban population exceeding 900 million, “even a small area of land subsidence in China could pose a significant threat to urban life,” the research team stated.
Tianjin, home to over 15 million people, has been identified as one of the most severely affected areas. Last year, 3,000 residents were forced to evacuate after a “sudden geological disaster”, which investigators attributed to groundwater depletion and geothermal extraction.
Many former coal-mining regions in China are also suffering from subsidence. Authorities in these areas are often compelled to pump concrete into collapsed coal mines to stabilize the ground.
Subsidence has cost China more than 7.5 billion yuan (approximately 1.04 billion USD) annually. It is predicted that in the next century, nearly a quarter of coastal areas may be below sea level, putting hundreds of millions of people at greater risk of flooding.
Expert Robert Nicholls from the Tyndall Centre for Climate Change Research at the University of East Anglia in the UK remarked that subsidence is indeed a national issue in China. “It is also a microcosm of what is happening around the world,” Nicholls added.
Another study published last February revealed that approximately 6.3 million square kilometers of land globally are at risk of subsidence. Among the most severely affected countries is Indonesia, where much of the capital Jakarta is now below sea level.
According to Nicholls, cities can learn from Tokyo, Japan, which experienced subsidence of about 5 meters until authorities banned groundwater extraction in the 1970s.
