Shanghai

Shanghai stands on hundreds of metres of soft, water-saturated Yangtze sediment that engineers nickname tofu soil. Subsidence was first measured here in 1921. As factories pumped groundwater the urban core dropped by as much as 2.6 metres by 1965, and at its worst, between 1956 and 1959, the ground fell about 98 millimetres a year.

From 1963 the city restricted pumping and began injecting water back into the aquifers. By 1985 urban subsidence had slowed to roughly a millimetre a year. Construction and suburban pumping restarted it after 1986, and a 2013 municipal regulation created dedicated control zones to manage it.

The legacy is a city sitting below its own storm tides. Around 480 kilometres of floodwall line the Huangpu, built in the 1980s to a one-in-a-thousand-year standard, and 508 kilometres of seawall face the estuary. A tidal gate guards the mouth of Suzhou Creek. The Bund's promenade is, in effect, a flood defence you can walk along.

At the eastern tip of Chongming, an island built entirely from Yangtze silt, lie the tidal mudflats and reedbeds of the Chongming Dongtan Bird National Nature Reserve. In July 2024 UNESCO inscribed it as part of the Migratory Bird Sanctuaries along the Coast of the Yellow Sea and Bohai Gulf. It is Shanghai's first World Heritage Site.

The Yellow Sea is a bottleneck for more than a tenth of all movement on the East Asian-Australasian Flyway, which links the Arctic to Australasia across some twenty-five countries. Researchers at Fudan University count around a million migratory bird visits to Dongtan a year, and 300 species have been recorded here. Shorebirds pass through in spring, and ducks and cranes winter on the flats.

Dongtan is also the site of China's most famous unbuilt eco-city. A zero-carbon plan for half a million people stalled in 2008, and the island's later eco-island programme absorbed some of what survived of it.

The treaty that ended the First Opium War forced Shanghai open to foreign trade in 1843. British and American concessions, later merged into the International Settlement, and a separate French Concession grew along the Huangpu north of the walled Chinese county town.

The Bund's granite banks, customs house and hotels went up mostly between the 1900s and the 1930s. It is architecture of commerce and of occupation, and the two are not separable. Across the river, Pudong was farmland and warehouses until the central government announced its development in April 1990.

Lujiazui's towers now stand on that ground. The Shanghai Tower, finished in 2015, rises 632 metres on a concrete raft above roughly a thousand bored piles driven some 85 metres down to firmer strata. The skyline is itself an engineering answer to the mud beneath it.