Almost half of China's urban areas are sinking. This increases the risk of flooding for millions of people. The USA is also at risk.
Beijing – China is the country of superlatives. Nowhere else in the world do so many skyscrapers reach into the sky, including cities like Beijing, Shanghai and Hong Kong. However, a current study shows that the conditions for such metropolises are more than unsuitable.
The ground beneath megacities is sinking – Beijing is particularly affected
The ground is sinking in many cities. This particularly increases the risk of flooding for cities with millions of inhabitants on the coasts. According to a report in the scientific magazine
Science,
almost 45 percent of China's urban areas are affected, especially the capital Beijing. Scientist Zurui Ao and his team from South China Normal University in Foshan analyzed satellite data from 82 major Chinese cities from 2015 to 2022.
The result: About a third (29 percent) of the residents of these cities experience ground subsidence of more than three millimeters. The researchers estimate that a total of 920 million people lived in China's urban areas in 2020, about 270 million of them on sinking land. In Shanghai alone, some areas have sunk by up to three meters in the last century.
The scientists warn of the long-term effects of ground subsidence, especially in densely populated coastal regions. They predict that the combination of land subsidence and rising sea levels could cause around a quarter of the area below sea level to sink in the next hundred years. This would pose a significant flood risk to large populations. There is also direct damage to buildings, foundations, infrastructure and sewage systems. The east coast of the USA is also at risk of increasing flooding, especially New York.
Scientists sound the alarm: “Strictly control groundwater extraction”
Land subsidence is associated with several factors, including groundwater extraction and the weight of buildings. The researchers point out that in recent decades China has experienced one of the fastest and most extensive urban expansions in human history. More and more cases of ground subsidence are already being reported in large cities. In recent decades, subsidence-related disasters in China have caused hundreds of deaths and injuries annually, as well as immense economic damage.
The study's research team emphasizes: "The results underline the need to strengthen protective measures and strictly control groundwater extraction." Long-term controls and more sustainable water management, as is already being successfully implemented in the Japanese cities of Tokyo and Osaka, could also help to stabilize the subsidence rate in China.
Venice and Mexico City are also affected by ground subsidence
Land subsidence is a global phenomenon that causes significant problems. It is often caused by overexploitation of groundwater, intensive development or oil and gas extraction. But natural, geological factors also play a role. Cities such as Venice, Italy and Mexico City, Mexico are known for their problems with ground subsidence. Venice is therefore even at risk of being classified as an endangered world heritage site again.
However, there are also parts of the world where opposite processes are taking place. For example, the ongoing uplift of land areas that were freed from the weight of the ice sheet of the last ice age
. (dt/asc/dpa)