Despite being virtually surrounded by water, the city is facing a serious water shortage and the Shanghai Water Affair Bureau concedes that demand has almost reached the present supply limit. Some climate change experts have warned that Shanghai will need to use desalinated water within 10 years, as well as import water from south-west China. Excessive pumping of water from underneath the city coupled with overdevelopment of skyscrapers has resulted in Shanghai sinking by an average of 10mm per year. The city has sunk more than two metres since 1921 and the government has limited building heights and begun pumping water back underground in an effort to stop the trend.­­­­