Land subsidence is a hazard in cities that is often overlooked, according to scientists from the University of East Anglia and Virginia Tech. In a comment article published in the journal Science, Prof Robert Nicholls and Prof Manoochehr Shirzaei highlight the importance of new research that accurately maps land movement across China using satellite data. They emphasize that while measuring subsidence is a significant achievement, more must be done to predict future subsidence by considering all drivers, including human activities and climate change.
The research paper, also published in the same issue, analyzed 82 cities in China with a total population of nearly 700 million people. The results show that 45% of these urban areas are sinking, with 16% experiencing a subsidence rate of 10mm or more per year. This affects roughly 270 million urban residents nationally, with nearly 70 million experiencing rapid subsidence of 10mm or more per year. Hotspots for subsidence include Beijing and Tianjin, particularly in coastal cities like Tianjin where sinking land reinforces climate change and sea-level rise.
The impact of subsidence on cities is significant, jeopardizing the structural integrity of buildings and critical infrastructure, and exacerbating the effects of climate change, especially in coastal areas. Prof Nicholls, whose research focuses on sea-level rise, coastal erosion, and flooding, emphasizes the need for a strong societal response to address this issue. Human activities, particularly groundwater withdrawal, are the main drivers of subsidence in cities, along with factors such as geology and building weight. Mitigation strategies, such as stopping groundwater withdrawal in cities like Osaka and Tokyo, have proven effective in reducing or ceasing city subsidence.
While human-induced subsidence was already known in China, the new research results further underscore the need for a national response to this widespread problem. Profs Nicholls and Shirzaei stress the importance of moving from measurement to understanding the implications of subsidence and supporting responses. They call for the research community to work with city planners to address subsidence issues using the detailed satellite data now available. Coastal cities in China and beyond need particular attention, as subsidence combined with sea-level rise could have catastrophic consequences if not addressed.
In cities like Shanghai, subsidence has led to the city sinking up to 3m over the past century, with continued subside today. When combined with sea-level rise, urban areas in China below sea level could triple in size by 2120, affecting millions of residents. This highlights the urgent need for cities to develop strategies for managing the risks of subsidence, which is more common than currently recognized. By learning from experiences dealing with climate change and sea-level rise, cities worldwide can better prepare for the threat of subsidence and work towards effective solutions for this widespread issue.
