A team of international scientists have expressed grave concern at the rate that the Chinese capital is sinking into the earth due to the excessive pumping of groundwater located below the city's surface.
The group of researcher from China, Spain and Germany analysed data gathered by means of satellite imaging as well as global positioning sensors to assess the rate of land subsidence in Beijing during the period from 2003 and 2011.
According to their shock findings the Chaoyang district of Beijing, which hosts the Chinese capital’s high-rise central business district, is sinking into the earth faster than any other part of the city, at a rate in excess of four inches per annum.
Their study also concluded that the ground level of certain parts of the city has slumped by more than a foot during just the eight year period covered by their research.
The researchers pointed to poor water management as the primary culprit for Beijing’s sinking ground levels. The depletion of groundwater aquifers as a result of excessive pumping can trigger land subsidence, as it causes irreversible consolidation of the earth by changing the level of effective stress that keeps the soil in a rigid state.
While records indicate that Beijing has suffered from land subsidence since the 1930’s, the problem has worsened severely of late as the city’s population has exploded to in excess of 20 million people, placing immense strain upon the surrounding region’s scarce water resources.
The researchers plan to release a follow-up study later this year of the impact of land subsidence on key infrastructure in Beijing, including China’s much vaunted high speed rail system.
Beijing is far from alone in suffering from severe land subsidence due to excessive groundwater pumping. According the researchers there are a total of 45 cities around China that suffer from “disastrous” levels of land subsidence.
The problem also afflicts a significant number of major population centres outside of China – in particular the megacities of emerging economies where booming urbanisation has placed heavy stress on water resources.
Other cities similarly afflicted by land subsidence included Mexico City, the Jakarta in Indonesia and the Thai capital of Bangkok. California’s San Joaquin Valley, host to a number of medium-sized cities, suffers from some of the world’s worst land subsidence, due to the pumping of groundwater over multiple generations by the farming sector.
Australia’s urban centres would at first glance appear to be a prime candidate for land subsidence, due to the dry, arid nature of the continental land mass, as well as the economy’s flourishing agricultural sector. According to Professor Will Featherstone from the WA School of Mines at Perth’s Curtin University, however, our major cities have little to fear when it comes to sinking ground levels.
Featherstone notes that while some parts of Australia are susceptible to land subsidence, the rates are so low that they pose no threat to settled areas or associated infrastructure.
“Perth and Adelaide are susceptible to land subsidence due to ground water usage – Perth derives as much as 70 per cent of its domestic water from the ground,” said Featherstone to Sourceable. “It’s not really a problem for these cities, however, because the subsidence is slow and small – typically only a few millimetres a year, and not enough to cause cracks in buildings or roads.
“Over the very long term you may see increased coastal erosion, but any problem that might concern us would require quite a lengthy time scale.”
In the case of Beijing, the loss of over a foot of ground level in under a decade has compelled the Chinese government to adopt strong measures to avert further damage.
The only truly effective means of preventing land subsidence is to restrict the depletion of groundwater that causes the problem. To this China’s State Council launched a plan in 2012 to staunch the use of groundwater as well as scrutinise afflicted areas, while the Chaoyang district has already announced the closure of 367 of its water wells to cut down on consumption.
The completion of the South-North Water Diversion project last year is also expected to significantly alleviate Beijing’s land subsidence dilemma, via the channeling of 44.8 billion cubic metres of water per annum from southern China’s Yangtze River to the country’s arid north.