The city of Beijing is sinking by as much as four inches or 11 centimeters each year, warns a study published on June 2 in the journal Remote Sensing. The study’s international research team, led by Beijing-based researchers, identifies the depletion of the city’s groundwater as the cause, which cause the soil to dry out and compact, a process known as subsidence.

The study states that this threatens the safety of the public and urban infrastructure. The sinking could destroy buildings, trains and other structures in the city.

The researchers from Spain, Germany and China explain that the city’s central districts are the worst affected areas. The study authors cite that the city’s Chaoyang district, where Beijing’s Central Business District is located, is the worst affected, plummeting at a rate of more than four inches annually. The district has fallen up to 30 inches between 2003 and 2011.

Beijing

Beijing Railway Station. Credit: Mike Stenhouse/Wikimedia

Beijing contains aquifers, a layer of permeable rock through which groundwater flows. However, as the city’s population increased as well as its water demand, the water reserves diminish over time, drying up the rock layer at an alarming rate beginning in the 1930s.

Groundwater comprises two thirds of the city’s water source. Beijing, currently populated by 20 million people, is fifth among the most water stressed city in the world, using 3.5 billion liters of water each year.

The researchers used satellite and GPS data for their study. They assessed the topographical changes in Beijing between 2003 and 2011.

The team told The Times that other cities are also experiencing the same problems. These include Bangkok, Mexico City, Jakarta and the San Joaquin Valley.

Nevertheless, China’s government have made measures to solve this issue. In 2012, China’s State Council approved a plan that regulated the use of groundwater.

In 2015, the country built tunnels and canals to bring water to Beijing, a project known as the South-North Water Diversion project. The Chaoyang district also stated that it will decrease its groundwater use by avoiding the use of the 367 water wells.

As of now, however, the researchers cannot tell if these actions can prevent land subsidence in Beijing.