China's cities are sinking and the risk of flooding is increasing. Several million residents are affected by the alarming development.
Beijing – The ground beneath many cities in China is sinking. This increases the risk of flooding for metropolises with millions of inhabitants on the country's coast. According to a report in the journal
Science,
almost 45 percent of urban areas in China are affected - especially the Chinese metropolis of Beijing.
China is sinking: several million residents are affected
Scientist Zurui Ao and his team from South China Normal University in Foshan analyzed satellite measurements from 82 major Chinese cities for the period from 2015 to 2022. About a third (29 percent) of the population in these cities is affected by a subsidence of more than three millimeters . According to researchers' estimates, a total of 920 million people lived in China's urban areas in 2020 - around 270 million of them live on subsiding land. In Shanghai alone, some areas have sunk by up to three meters in the last century.
The researchers warn that the ground subsidence could have long-term consequences, especially in densely populated coastal regions. Due to the combination of ground subsidence and rising sea levels, around a quarter of the areas there could sink below sea level 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 sinking into the sea - the risk of flooding is high in the affected regions.
China's sinking could have serious consequences - protective measures must be strengthened
Soil 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. Cases of ground subsidence are already increasingly 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 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 worldwide phenomenon that causes significant problems. It is often caused by human activities such as 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, in some parts of the world there are also opposing processes, such as the ongoing uplift of land areas that were freed from the weight of the ice sheet of the last ice age.
(dt/dpa)