Rising sea levels and sinking land is not a good combination. Like many densely populated coastal areas, Shanghai will have to deal with the effects of climate change. This article is from South China Morning Post.
Shanghai rose from the sea and grew into a modern showcase, with skyscrapers piercing the clouds, atop tidal flats fed by the mighty Yangtze River. Now a city of 20 million, its future depends on finding ways to prevent the same waters from reclaiming it.
Global warming and melting glaciers and polar ice sheets are raising sea levels worldwide, leaving tens of millions of people in coastal areas and on low-lying islands vulnerable to flooding and other weather-related catastrophes.
Shanghai, with an altitude roughly three metres above sea level, is among dozens of great world cities – including London, Miami, New York, New Orleans, Mumbai, Cairo, Amsterdam and Tokyo – threatened by sea levels that are rising twice as fast as projected just a few years ago, expanding from warmth and meltwater. Estimates of the scale and timing vary, but Professor Stefan Rahmstorf, a respected expert at Germany’s Potsdam Institute, expects a one-metre rise in this century and up to five metres over the next 300 years.
Chinese cities are among the largest and most threatened. Their huge populations – the Yangtze River Delta region alone has about 80 million people – and rapid growth into giant industrial, financial and shipping centres could mean massive losses from rising sea levels, experts say.
The sea is steadily advancing on Shanghai, tainting its freshwater supplies as it turns coastal land and groundwater salty, slowing drainage of the area’s heavily polluted flood basin and eating away at the delta soils that form the city’s foundations.
Planners are slow in addressing the threat, in the apparent belief they have time. Instead, Shanghai has thrown its energies into constructing billions of yuan worth of new infrastructure – ports, bridges, airports, industrial zones – right on the coast.
“By no means will Shanghai be under the sea 50 years from now. It won’t be like The Day after Tomorrow scenario,” said Professor Zheng Hongbo, a geologist who heads the School of Earth Science and Engineering at Nanjing University, referring to a Hollywood movie on an abrupt global warming that leads to a new ice age. “Scientifically, though, this is a problem whether we like it or not,” said Zheng, pointing to areas along Shanghai’s coast thought to be shrinking because of erosion due to rising water levels.
Chinese legend credits Emperor Yu the Great with taming floods in Neolithic times by dredging new river channels to absorb excess water. In modern times, the city has been sinking for decades, thanks to pumping of groundwater and the construction of thousands of high-rise buildings.
Today, Shanghai’s engineers are reinforcing floodgates and levees to contain rivers rising because of heavy silting and subsidence.
“We used to play on the riverbanks and swim in the water when I was growing up. But the river is higher now,” said Ma Shikang, an engineer overseeing Shanghai’s main floodgate, pointing to homes below water level near the city’s famed riverfront Bund.
Twice daily, the 100-metre barrier, where the city’s Suzhou Creek empties into the Huangpu River, is raised and lowered in tandem with the tides and weather, regulating the city’s vast labyrinth of canals and creeks.
The 5.9-metre-high floodgate is built to withstand a one-in-1,000-years tidal surge; the highest modern Shanghai has faced so far was 5.72 metres, during a typhoon in 1997.
Levees along the Bund and other major waterways are 6.9 metres high, providing better protection than in Miami, New York and many other cities. But they would still be swamped if hit by a surge like Hurricane Katrina’s 8.5-metre onslaught.
Shanghai is considering building still bigger barriers – like those in London, Venice and the Netherlands – to fend off storm surges, most likely at the point 30 kilometres downstream where the deep, muddy Huangpu empties into the Yangtze.
Sang Baoliang, deputy director of the Shanghai Flood Control Headquarters, has been to see the Thames Barrier, which protects London, and the Deltaworks series of storm barriers and dams in the Netherlands, where two-thirds of the population live on land below sea level, much of it reclaimed from the sea.
Like many mainland officials, some of whom deem the topic too sensitive to discuss, Sang is cautious about what China might do.
“We are studying this, but it is extremely complicated. If the research determines that indeed the sea level will rise further, then we will need to build the walls higher. But this is still under research.”
Such projects usually require several decades of planning and construction, and with sea levels rising, they are likely to have to be adjusted, given the unknowns of climate change.
“Nobody – no municipal or provincial government, and no central government agency – is preparing adaptation plans for Shanghai or the Yangtze delta,” said Edward Leman, whose Ottawa-based consultancy, Chreod, has published research on the issue. “They must begin now, as investments and decisions made today will have a major impact in the coming years.”
Nearly a quarter of mankind lives in low-lying coastal areas, and urbanisation is drawing still more people into them.
“The tendency of coastal and port locations to become playgrounds for architects and developers has become a global phenomenon in recent decades,” said Gordon McGranahan, director of the human-settlements group at the International Institute for Environment and Development, an independent think tank in London.
Though much of its land is arid, China likewise has millions of people living in densely populated tidal flats and coastal valleys who already must be evacuated during typhoons. Many of the country’s biggest cities are threatened, the OECD report says.
“What has been specific to China has been the enormous coastward migration, unfortunately just at a time when it would have been better not to settle low-elevation coastal areas,” McGranahan said.
In the future, communities unable to move may instead end up adapting buildings and infrastructure to accommodate higher water levels, said Hui-Li Lee, a landscape architect working on projects in the region.