Satellite Data Uncovers an Alarming Subsidence Risk Across Chinese Cities
New cutting-edge research employing satellite technology has shed light on a growing problem facing China’s urban environments. A significant portion of the country’s city areas, encompassing about a third of its urban population, are sinking, posing substantial risks to millions of people and the infrastructure they rely on.
This advanced satellite survey extensively monitored land movement patterns across China, uncovering that nearly half of the urban territories are affected by subsidence. Alarmingly, about 16% of these territories are descending at a swift pace, exceeding 10mm per year. In real terms, this puts approximately 270 million residents at risk, with 70 million of them residing in areas where the ground is rapidly sinking beneath their feet.
Cities like Beijing and Tianjin have been pinpointed as significant concern areas, with coastal cities such as Tianjin also grappling with the dual threats of subsidence and sea level rise. Historical events have shown the catastrophic potentials of such situations, drawing parallels to major natural disasters like Hurricane Katrina’s impact on New Orleans.
Among the cities, Shanghai stands out for its striking rate of land descent, having sunk by as much as 3 meters during the past century. The situation appears increasingly concerning with projections indicating that the expanse of urban areas below sea level in China is likely to triple by the year 2120. This could adversely affect between 55 to 128 million people, marking a staggering increase in risk levels.
The origins of subsidence are deeply rooted in the excessive extraction of groundwater. This process diminishes the water table and, combined with the weight of densely packed urban environments and the type of geological substrates, contributes significantly to the problem. Examples from cities like Osaka and Tokyo demonstrate that policies limiting groundwater removal have effectively mitigated, if not completely reversed, the subsidence issue.
While the focus of this research is on China, it’s clear that the issue of urban subsidence is not confined within national borders. It is a global challenge that threatens cities worldwide, necessitating immediate and coordinated global action.
The shift proposed by researchers is not merely to continue monitoring subsidence but to develop and execute comprehensive mitigation strategies. This would involve collaboration among city planners, policymakers, and various stakeholders to address the subsidence risks head-on. According to the study, the primary goal should be not only to protect the structural integrity of urban infrastructure but also to combat the aggravated effects of climate-induced flooding, especially in vulnerable coastal areas.
The findings are a call to action for both national and international communities, underscoring the imperative of integrating responses to subsidence with broader climate change mitigation and adaptation efforts. As urban populations continue to swell, and infrastructures bear the growing weight of development, the challenge of ground subsidence intertwines with the existential threat of climate change, demanding urgent and innovative responses.
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