过度抽取地下水导致北京正在下沉 central, 北京, 地下水

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China's capital is known for its horrendous smog and occasional sandstorms. Yet one of its major environmental threats lies underground: Beijing is sinking.

北京可怕的雾霾和偶尔发生的沙尘暴为世人皆知，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.

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.

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. 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."

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.

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.
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