China’s rampant groundwater extraction is one of the primary factors for subsidence, researchers said. Cities have been pumping water from underground aquifers faster than it can be replenished, a situation exacerbated by climate change-fueled drought. Excessive pumping lowers the water table and causes the overlying land to sink.
The land is also sinking due to the growing weight of cities themselves. Soil can compact, naturally from the weight of sediments accumulating over time and from heavy buildings pressing down on the ground, causing the land to steadily sink.
Land subsidence isn’t just a problem in China. In the US, dozens of coastal cities, including New York City, are sinking. In the Netherlands, 25% of its lands have sunk lower than sea levels. And in Mexico City, likely the world’s fastest subsiding city, land is sinking at the speed of up to 50 centimeters, or nearly 20 inches, a year.
The impact of sinking is typically worse along the coasts, where the sea level is rising at the same time. This combination exposes more land, people and property to destructive flooding.
The study suggests roughly a quarter of China’s coasts will be lower than sea level because of subsidence and projected sea level rise, priming the area for colossal damage and putting lives at risk. Tianjin, Shanghai and areas around Guangzhou are significantly exposed to both issues, the study found.