In a study published in Science, Prof Robert Nicholls from the Tyndall Centre for Climate Change Research at UEA and Prof Manoochehr Shirzaei from Virginia Tech, alongside the United Nations University for Water, Environment and Health in Ontario, present new findings from satellite surveys that consistently track land movement across China.
The study reveals that 45% of the urban regions surveyed are experiencing subsidence, with 16% of these areas subsiding at a rapid pace of more than 10mm annually. This translates to about 270 million people living in affected areas, nearly 70 million of whom are in zones sinking rapidly.
Beijing and Tianjin are identified as major hotspots, while coastal cities like Tianjin face compounded risks as subsidence amplifies the effects of sea-level rise. Historical examples such as the devastation from Hurricane Katrina in New Orleans underscore the potential threats of such phenomena.
The most severe cases include Shanghai, which has sunk by up to 3 meters over the last century and continues to subside. Projections suggest that the urban area below sea level in China could triple by 2120, potentially impacting between 55 and 128 million people.
The primary cause of subsidence is identified as groundwater extraction, which lowers the water table, along with factors like the geological substrate and the weight of urban structures. Cities like Osaka and Tokyo have shown that curtailing groundwater withdrawal can significantly reduce or halt subsidence.
While the study emphasizes the critical nature of the problem in China, it also highlights that this is a global issue, with other cities around the world similarly at risk.
The researchers advocate for a shift from simply measuring subsidence to developing comprehensive strategies involving city planners and other stakeholders to mitigate these risks effectively.
"Subsidence is undermining the structural integrity of buildings and infrastructure, worsening the impacts of climate-related flooding, especially in coastal regions," said Prof Nicholls. This research underscores the urgent need for integrated national and global responses to the challenges of urban subsidence alongside climate change.
Research Report:Earth's sinking surface: China's major cities show considerable subsidence from human activities
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