The city of Beijing is sinking at a rate of up to 11 centimeters (4 inches) per year, according to a new study in the journal Remote Sensing. The cause of this perplexing plummet, say the researchers, is that the city’s groundwater has become depleted, causing soil to dry out and compress.
The study notes that Beijing is largely hydrated by underground reserves of permeable rock that transmit groundwater, known as aquifers. However, a surge in population, industry, and agriculture in the surrounding area has diminished these subterranean water reserves, causing the city to begin sinking in the 1930s.
Naturally, this is not helped by the fact that the Chinese megacity – which has a population of around 20 million – is laden with the weight of urban congestion and development. It is therefore unsurprising that Beijing’s financial district, where many of its skyscrapers are located, is among the most rapidly sinking neighborhoods.
Using satellite imagery and GPS data, the study authors were able to analyze topographical changes across the Chinese capital from 2003 to 2010, noting that the city is indeed descending. Though Beijing is far from the only sinking metropolis – Mexico City and Venice are two other examples – the fact that it is the fifth most water-stressed city on the planet suggests that the possibility of this trend continuing is high.
As the city’s residents continue to guzzle up around 3.5 billion liters (925 million gallons) of groundwater each year, the researchers are now concerned that the sinking streets could soon cause damage to buildings, railways, and other vital infrastructure.
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