The Chinese capital of Beijing is ridden with heavy smog and air pollution, but toxic pollutants aren't the only ones afflicting the city.

Using cutting-edge satellite imagery, a team of scientists discovered that Beijing is slowly sinking, and parts of its central business district are descending by 11 centimeters (4.3 inches) annually.

Researchers point to the excessive pumping of groundwater underneath the city as the culprit for Beijing's slow collapse.

Subsidence In Beijing

Beijing lies in a dry plain where groundwater has collected for more than thousands of years. Experts say that like a dried-out sponge, the underlying soil compresses as wells are punctured and the underground water drops.

Researchers have found that the entire city is sinking, but the impact is much more pronounced in the Chaoyang district, which grew since the 1990s with ringroads, skyscrapers and other infrastructure. The uneven nature of the sinking in some areas of Beijing poses risks to these buildings, researchers report.

In and around Beijing, scientists believe that there are thousands of water wells and most of them are used in landscaping and farming. Although the state has authority over the installation of wells, a Chinese environmentalist says it is inconsistent in applying this regulatory power.

"There are some rules, but the enforcement is doubtful," says Director Ma Jun of the Institute of Public and Environmental Affairs in Beijing.

Ma says he was not surprised that subsidence was relatively high in the Chaoyang district, especially because of its rapid growth in recent years. He expects it to keep moving east as the city is sprawled in that direction.

Implications To The City

Researchers warn that if the subsidence or sinking continues, Beijing's population of 20 million will face a great safety threat, with the city's train operations severely affected.

Fortunately, the state is conducting efforts to alleviate the issue. In 2015, China launched a mega-engineering project with the goal of mitigating the water crisis in Beijing.

The government completed the construction of a £48-billion ($65 billion), 2,400-kilometer (1,491 miles) network of tunnels and canals. These were designed to divert 44.8 billion cubic meters (1.6 trillion cubic feet) of water to the capital.

Even before the canal project began, the city was easing up on groundwater pumping. In January 2015, the Chaoyang district planned to remove more than 360 water wells that would reduce 10 million cubic meters (353 million cubic feet) of underground water.

Whether this is enough is too early to know, experts say. In the meantime, the team of seven researchers, who explained their findings to The Guardian, say they are currently carrying out further analysis on the possible impacts of subsidence on infrastructure in the Beijing plain.

The team's full findings, initially peer-reviewed in the journal Remote Sensing, will be published later this year.

Photo: Nikolaj Potanin | Flickr

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