Shanghai, one of the world's largest coastal cities, has sunk more than two meters over the past century. The main cause is heavy groundwater pumping combined with soft, compressible soil. This sinking raises the risk of floods, sea-level rise, and damage to buildings and roads. Experts say the city's sinking is not sudden but slow and steady. The biggest subsidence was in the mid-20th century when groundwater was pumped heavily for industry and farming. Some areas sank by 10 to 15 centimeters a year back then. To fight this, Shanghai's officials have cut groundwater pumping, shifted water extraction to deeper sources, and started injecting treated river water back into underground layers. This method, called artificial recharge, helps lift water pressure in the soil, which supports the land and slows sinking. Today, subsidence has dropped to about one centimeter per year. Though the city is not rising, the drop in sinking speed helps reduce flood danger and protect infrastructure like roads and subways. This technique is inspired by similar programs in places like Long Beach, California, where pumping water into old oil zones reduced land loss. Scientists warn that much of the sinking is permanent, and risks remain, such as small earthquakes triggered by water injection. That's why Shanghai uses GPS and satellite monitoring to watch the ground carefully. Shanghai is a warning example for many growing low-lying cities worldwide facing sinking and rising seas. Managing underground water wisely can help protect millions of people and costly infrastructure from climate threats.