中国的首都北京以可怕的雾霾和偶尔发生的沙尘暴远近闻名。而一个重要的环境威胁却被大家忽略了：北京正在下沉。

Excessive pumping of groundwater is causing the geology under the city to collapse, according to a new study using satellite imagery that reveals parts of Beijing – particularly its central business district – are subsiding each year by as much as 11 centimetres, or more than four inches.

一项根据卫星图像作出的最新研究结果显示，过度抽取地下水导致北京地下结构出现塌陷。北京部分地区，特别是中央商务区，每年下沉多达11厘米，也就是超过4英寸。

The authors of the study warn that continued subsidence poses a safety threat to the city of more than 2o million, with "a strong impact on train operations" one of the predictions.

研究报告的作者提醒道，持续的下沉对这座人口超过两千万的城市构成了安全威胁，其中一个预测就是"将对列车运行造成很大影响"。

北京过度抽取地下水 每年下沉11厘米

The study on Beijing's subsidence has been published in the peer-reviewed journal Remote Sensing and is based on InSAR, a type of radar that monitors land elevation changes.

这项有关北京下沉的研究发表在同行评议期刊《遥感科学》上。研究基于干涉合成孔径测量技术，这是一种监测地面高程信息变化的雷达技术。

It was written by a team of seven researchers. "We are currently carrying out a detailed analysis of the impacts of subsidence on critical infrastructure (eg high-speed railways) in the Beijing plain," they said in an email to the Guardian. "Hopefully a paper summarising our findings will come out later this year."

该报告是由7位成员组成的一研究小组发布的。他们在给《卫报》的一封电邮中写道："我们目前正在进行一项北京平原地区地表下沉对关键基础设施影响的详细分析（比如高铁）。希望能在今年晚些时候发表一份能概括我们研究结果的论文。"

Beijing sits in a dry plain where groundwater has accumulated over millennia. As wells are drilled and the water table drops, the underlying soil compacts, much like a dried-out sponge.

北京坐落于干燥的平原地区，这儿的地下水经过了数千年的累积。随着钻井抽取地下水，地下水位有所下降，地下的土壤更加紧密，就像干涸的海绵一样。

The study finds that the entire city is sinking but the subsidence is most pronounced in Beijing's Chaoyang district, which has boomed since 1990 with skyscrapers, ringroads and other development. The researchers say the uneven nature of the subsidence in some areas poses risks to buildings and other infrastructure.

研究发现，整个城市都在下沉，而朝阳区下沉最严重。自上世纪90年代以来，朝阳区繁荣发展，高楼大厦和环路不断涌现。研究人员表示，一些地区下沉不均匀的特性会对建筑物和其他基础设施造成威胁。

Tens of thousands of water wells are thought to exist in and around Beijing, many of them used in farming and landscaping. The state has regulatory power over installation of wells but is inconsistent in applying it, according to one leading Chinese environmentalist.

据悉，北京及周边地区有数万口水井，其中很多用于农田灌溉和绿化。国家对打井有监管权，但据一位领头的环保人士表示，实际执行情况并不理想。

"There are some rules but the enforcement is doubtful," said Ma Jun, director of the Institute of Public and Environmental Affairs in Beijing. Ma said he wasn't surprised subsidence was relatively high in the Chaoyang district given its rapid growth of recent decades. He expected it to keep moving east as the city sprawled in that direction.

公众环境研究中心主任马俊说道："确实有一些监管规则，但执行成效令人怀疑。"马俊表示，他对朝阳区地表下沉速度更快并不惊讶。因为朝阳区近几十年来发展非常快。他预计随着整个城市向东扩展，地表下沉将会继续向东延伸。

Other cities around the world are experiencing subsidence caused by excessive water pumping or other factors. Mexico City is sinking by up to 28cm a year. Bangkok is dropping annually by as much as 12cm, similar to Beijing, according to the Remote Sensing researchers.

根据《遥感科学》的研究人员表示，世界上许多其他城市也受到了过度抽取地下水或其他因素导致的地表下沉的困扰。墨西哥城每年下沉多达28厘米，曼谷每年下沉达12厘米，与北京类似。