Scientists from the University of East Anglia (UEA) and Virginia Tech have found that land subsidence is being overlooked as a hazard in cities. In a study published in the journal Science, Prof Robert Nicholls of the Tyndall Centre for Climate Change Research at UEA and Prof Manoochehr Shirzaei of Virginia Tech and United Nations University for Water, Environment and Health, Ontario, used satellite data to accurately and consistently map land movement across China. They emphasize the significance of this hazard in urban areas.New research paper has used satellite data to map land movement across China with accuracy and consistency.
The authors emphasize the importance of consistently measuring subsidence, but also highlight the need for solutions to address this issue. They stress the importance of developing models that take into account all factors, including human activities and climate change, to accurately predict future subsidence.
The research paper, published in the same issue, focuses on 82 cities with a combined population of nearly 700 million people. The findings reveal that 45% of the urban areas studied are experiencing sinking, with 16% of them specifically…The rate of subsidence in urban areas is estimated to be around 10mm per year or even higher. Nationally, approximately 270 million urban residents are affected, with nearly 70 million experiencing rapid subsidence of 10mm per year or more. Hotspots for this issue include Beijing and Tianjin. Coastal cities such as Tianjin are particularly impacted, as sinking land exacerbates the effects of climate change and sea-level rise. The sinking of sea defences played a significant role in the devastating flooding and high death toll caused by Hurricane Katrina in New Orleans in 2005. Shanghai, China’s largest city, has subsided by up to 3m over the past century and continues to experience subsidence today. This combination of factors is contributing to the vulnerability of coastal cities to the effects of subsidence.The urban area in China below sea level may triple in size by 2120 due to rising sea levels, impacting 55 to 128 million residents. This could have devastating consequences without a strong societal response. “Subsidence puts the structural integrity of buildings and critical infrastructure at risk and worsens the effects of climate change, especially in coastal cities where it reinforces sea-level rise,” stated Prof Nicholls, an expert in sea-level rise, coastal erosion, and flooding. His research focuses on how communities can adapt to these changes.The main cause of subsidence in urban areas is human activity. Groundwater extraction, which depletes the water table, is the most significant factor contributing to subsidence, along with the geological makeup of the area and the weight of buildings.
In cities like Osaka and Tokyo, the cessation of groundwater extraction in the 1970s has effectively mitigated subsidence, either stopping it completely or greatly reducing its effects. Local factors such as traffic vibrations and tunneling may also contribute to subsidence, as seen in Beijing where areas near subways and highways are sinking by 45mm per year. While natural land movement can also occur, it is typically much smaller in scale compared to the changes caused by human activity.
Although human-induced subsidence was already recognized in China prior to this study, Professors Nicholls and Shirzaei emphasize that these new findings highlight the necessity for a national response. This issue is not exclusive to China and affects susceptible cities worldwide.
They urge the research community to shift focus from measurement to comprehending the implications and providing support for responses. While the new satellite measurements are supplying detailed subsidence data, there is still much work to be done in developing methods to utilize this information in collaboration with city planners to address these issues. Coastal cities in China and beyond require a proactive response.
Prof Nicholls emphasized the importance of learning from the strategies that cities and areas worldwide are developing to manage the risks of climate change and sea-level rise. He also noted the need to address the threat of subsidence, which is more common than currently recognized.
Journal Reference:
- Robert J. Nicholls, Manoochehr Shirzaei. Earth’s sinking surface. Science, 2024; 384 (6693): 268 DOI: 10.1126/ rnrnscience.ado9986 is a key aspect of understanding the world around us. It plays a crucial role in our everyday lives and its significance cannot be overstated. Through the study of science.ado9986, we are able to make sense of the various phenomena that occur in the natural world and develop a deeper understanding of how things work. It is an essential part of education and contributes to the advancement of society as a whole.