Nearly a quarter-billion Chinese live in major cities with moderate to severe subsidence that researchers say puts them at greater risk for flooding and other disasters in the coming decades.
Subsidence, or sinking of the Earth's surface, is a result of excessive groundwater extraction and the immense pressing weight of the expanding metropolises.
Coastal cities will be particularly vulnerable as climate change causes sea levels to rise. This will lead to more severe flooding and erosion threatening infrastructure, homes and ecosystems if sufficient action is not taken, experts said.
A Newsweek map illustrates the most affected metropolises, based on data from a study published last month in the peer-reviewed journal Science.
The five areas delineated by the dotted lines contain the fastest-sinking cities. They include the capital of Beijing and the bustling financial hub of Shanghai, home to more than 21 million and 26 million people, respectively.
The darker the color, the more severe the subsidence. In total, the urban centers depicted are home to more than 242 million people, or more than one-sixth of China's population.
The researchers relied on synthetic aperture radar (SAR) imagery, which uses satellite radar to detect even minor ground movements, for their observations of 82 cities.
Some 29 percent of the total population of these cities are estimated to live in areas sinking at a relatively moderate pace of more than 3 millimeters per year. Another 7 percent live in regions subsiding faster than 10 mm per year.
The researchers predicted that if subsidence rates remain unchanged, the proportion of land with a relative elevation below sea level will increase by a factor of 2.7 to 3.3 by 2100 compared to 2020 levels, "indicating the potential for widespread inundation unless well protected."
Disasters linked to subsidence have already resulted in hundreds of deaths and injuries annually, with economic losses exceeding $1 billion as of 2014, according to China Meteorological Administration (CMA) statistics.
Newsweek reached out to the CMA with a written request for comment.
Fissures caused by subsidence can inflict severe damage to infrastructure. Catastrophic flooding—such as what caused the evacuation of more than 100,000 people in the southeast province of Guangdong last month—is an even greater danger.
A dual approach of mitigation and adaptation is needed, Robert Nicholls, University of East Anglia climate adaption professor and director of the Tyndall Centre for Climate Change Research, previously told Newsweek.
For example, cities like Japan's Tokyo and Osaka have significantly slowed subsidence by cracking down on groundwater withdrawal. Shanghai has also had limited success reducing its subsidence, Nicholls pointed out.
"If subsidence cannot be mitigated, adaptation is necessary. This means defense or retreat," he said.
The academic added that coastal areas in China and other countries suffering from subsidence already have extensive dike systems in place, but they must be upgraded.
"Retreat or abandonment of land is possible but unlikely in China," Nicholls said.
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Micah McCartney is a reporter for Newsweek based in Taipei, Taiwan. He covers U.S.-China relations, East Asian and Southeast Asian ... Read more
