Nearly half of China’s major cities are sinking — some ‘rapidly’
中国近一半的主要城市正在下沉—有些“迅速”
Tens of millions of people in the country’s coastal lands might find their homes below sea level by 2120 owing to sinking and sea-level rise.
到2120年，由于下沉和海平面上升，该国沿海地区的数千万人可能会在海平面以下找到自己的家园。
One in ten residents of China’s coastal cities could be living below sea level within a century, as a result of land subsidence and climate change, according to a paper published in Science today1.
根据发表在《今日科学》杂志上的一篇论文，由于地面沉降和气候变化，中国沿海城市十分之一的居民可能在世纪内生活在海平面以下。
Some 16% of the mapped area of China’s major cities is sinking “rapidly” — faster than 10 millimetres every year. An even greater area, roughly 45%, is sinking at a “moderate” rate, the paper says, meaning a downward trajectory of greater than 3 mm annually. Affected cities include the capital Beijing, as well as regional capitals, including Fuzhou, Hefei and Xi’an.
中国主要城市地图上约16%的面积正在”迅速”下沉——每年下沉速度超过10毫米。报告说，更大的面积，大约45%，正在以“适度”的速度下沉，这意味着每年下沉超过3毫米。受影响的城市包括首都北京，以及福州，合肥和西安等地区首府。
The situation could see one-quarter of China’s coastal lands slip below sea level within a few decades, posing “serious threats” to the hundreds of millions of people who live on the coast, the paper notes.
报告指出，这种情况可能导致中国四分之一的沿海土地在几十年内滑入海平面以下，对生活在沿海地区的数亿人构成“严重威胁”。
That sinking feeling 那种下沉的感觉
“Subsidence is certainly not only a problem in China. Many other parts of the world share the same problem,” says Ding Xiaoli, a geodesist at the Hong Kong Polytechnic University.
“下沉当然不仅仅是中国的问题。世界上许多其他地方也有同样的问题，”香港理工大学的大地测量学家丁晓丽说。
Subsidence is when land sinks relative to sea level, usually owing to extraction of subsurface water, rock or other resources.
沉降是指陆地相对于海平面下沉，通常是由于地下水、岩石或其他资源的开采。
In the famously low-lying Netherlands, roughly one-quarter of the land has subsided to below sea level. And by 2040, almost one-fifth of the world’s population is projected to be living on sinking land.
在著名的低地荷兰，大约四分之一的土地已经沉降到海平面以下。到2040年，预计世界上近五分之一的人口将生活在下沉的土地上。
Jakarta has become the most rapidly subsiding capital in the world, prompting Indonesia to propose a new capital city.
雅加达已经成为世界上下沉最快的首都，这促使印度尼西亚提出了一个新的首都城市。
In the United States, more than 44,000 square kilometres of land across 45 states has been directly affected by subsidence, with more than 80% of the cases relating to groundwater extraction, often for agricultural purposes.
在美国，45个州超过44，000平方公里的土地直接受到沉降的影响，其中80%以上的情况与地下水开采有关，通常用于农业目的。
Ding says that the study provides an interesting snapshot of the situation in China, and crucially links the issue to the populations affected.
丁说，这项研究为中国的情况提供了一个有趣的快照，并将这个问题与受影响的人群联系起来。
The authors, led by Tao Shengli, a researcher in remote-sensing technology at Peking University in Beijing, assessed 82 cities across China with a population of more than 2 million. They used radar pulses from satellites to measure the changes in the distance between the satellite and the ground to examine how its elevations changed between 2015 and 2022.
由北京大学遥感技术研究员陶胜利带领的研究小组对中国82个人口超过200万的城市进行了评估。他们使用卫星的雷达脉冲来测量卫星与地面之间距离的变化，以研究其海拔在2015年至2022年之间的变化。
They found that the cities facing severe subsidence are concentrated in five regions, and cover both coastal and inland cities.
他们发现，面临严重沉降的城市集中在五个地区，包括沿海和内陆城市。
Also on the list are cities in the largely land-locked southwest, such as Kunming, Nanning and Guiyang — a finding that surprises Zhou Yuyu, a geographer at the University of Hong Kong. “These cities are not as densely populated or industrialized as some other parts of China, yet they still experience significant subsidence,” he says.
中国西南部的内陆城市也榜上有名，如昆明、南宁和贵阳。这一发现让香港大学地理学家周玉玉感到惊讶。他说：“这些城市不像中国其他地区那样人口密集或工业化，但它们仍然经历着严重的沉降。”
Losing ground 败退
The paper links a range of natural and human factors to sinking, such as the depth of a city’s bedrock, groundwater depletion, the weight of buildings, the use of transport systems and underground mining.
这篇论文将一系列自然和人为因素与下沉联系起来，比如城市基岩的深度、地下水的枯竭、建筑物的重量、交通系统的使用和地下采矿。
Previous studies2 have found that excessive groundwater extraction is a key cause of severe land subsidence in cities across the world.
先前的研究 2 发现，过度抽取地下水是世界各地城市严重地面沉降的关键原因。
But there are also stories of successful mitigation. Tokyo slowed its sinking from a rapid 240 mm a year in the 1960s to about 10 mm a year in the early 2000s, after passing laws that limited groundwater pumping. Shanghai, China, which sank by a staggering 2.6 metres between 1921 and 1965, reduced its annual rate of sinking to about 5 mm after implementing a series of environmental regulations.
但也有成功缓解的故事。在通过限制抽取地下水的法律后，东京的下沉速度从20世纪60年代的每年240毫米减缓到21世纪初的每年10毫米左右。中国上海在1921年至1965年间下沉了2.6米，在实施了一系列环境法规后，其年下沉率降至约5毫米。
“The key to addressing China’s city subsidence could lie in the long-term, sustained control of groundwater extraction,” the paper says.
“解决中国城市沉降问题的关键可能在于长期持续地控制地下水开采，”该论文说。
Ding says that, in cities such as Macao and Hong Kong where no groundwater is used, subsidence mainly comes from consolidation — downward movement as a result of soil being compressed — after land reclamation.
丁说，在澳门和香港等不使用地下水的城市，沉降主要来自土地开垦后的固结-由于土壤被压缩而向下移动。
The authors also listed the weight of buildings as a factor. Contrary to expectations, heavier buildings, such as the skyscrapers in Shanghai, tend to sink slower than lighter structures do, possibly because those buildings are anchored on deeper rock, according to the paper.
作者还将建筑物的重量列为一个因素。与预期相反，较重的建筑物，如上海的摩天大楼，往往比较轻的建筑物下沉得慢，可能是因为这些建筑物固定在较深的岩石上。
Double whammy 双重打击
As cities sink, global sea levels are also rising, owing to the effects of climate change. This double whammy will cause 22–26% of China’s coastal lands to drop below sea level by 2120, the paper says.
由于气候变化的影响，随着城市下沉，全球海平面也在上升。这份报告说，到2120年，这双重打击将导致中国22-26%的沿海土地低于海平面。
Wei Meng, a geophysicist at the Graduate School of Oceanography at the University of Rhode Island in Kingston regards the figures as “terrifying”.
位于金斯顿的罗得岛大学海洋学研究生院的海洋学家孟伟（音译）认为这些数据“令人恐惧”。
In 2022, Wei and his colleagues found that land was sinking faster than sea levels were rising in many coastal cities worldwide. They predicted that these cities would be challenged by flooding “much sooner” than timelines projected by sea-level models if they continued to sink at current rates.
2022年，魏和他的同事发现，在全球许多沿海城市，陆地下沉的速度比海平面上升的速度快。他们预测，如果这些城市继续以目前的速度下沉，它们将比海平面模型预测的时间表“更快”受到洪水的挑战。
Climate change might exacerbate sinking in other ways, such as by affecting where and when it rains — or doesn’t rain.
气候变化可能会以其他方式加剧下沉，例如影响下雨或不下雨的地点和时间。
“Increasing droughts can prompt excessive groundwater extraction, contributing to subsidence in urban areas,” Zhou says.
“日益严重的干旱会促使地下水过度开采，导致城市地区的沉降，”周说。
Dike systems could be a cost-efficient way to prevent inundation as cities’ elevations fall, the paper says.
论文说，随着城市海拔的下降，堤坝系统可能是防止洪水泛滥的一种具有成本效益的方法。