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Experts: Deep flooding unlikely to hit Shanghai
November 30, 2012, Friday
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EDITOR'S note:
This is the second and final part of an article by our reporters Zha Minjie and Ni Yinbin on the safety of densely populated Shanghai in the face of possible extreme weather.
Drainage is considered a city's "conscience," and a better indicator of sound planning than high-rise buildings.
Jiang Dahe, a professor at the UN Environment Program-Tongji Institute of Environment for Sustainable Development, said city management should "beware of the power of the nature and the damage it can do to big cities."
"The rainfall volume in Shanghai has gradually increased in the past 50 years and sudden and heavy torrents have been more frequent," says the latest report by Tongji University on climate change and the safety of the city's underground public facilities.
The current public drainage system can handle precipitation of 36 millimeters per hour once a year in most parts of the city, and 50 to 56 mm once every three to five years in key areas such as airports and important business areas.
Shortcomings
Underground structures such as subway entrances and passages are relatively better able to handle drainage problems than the rest of the city, on average. But there are shortcomings.
"The biggest problem is that facilities' design only considers the rainfall through entrances and ventilation," said Zhang Jing, a member of the Tongji report's research team. "It fails to calculate ground seepage or flood conditions."
According to the Intergovernmental Panel on Climate Change (IPCC), there is a consensus that extreme weather will occur to varying degrees in the near future because of greenhouse gases and global warming. Shanghai faces possible invasion of seawater during extreme weather, said Zhang from Tongji. In August alone, five typhoons threatened the city, a record number.
Shanghai was described as the most vulnerable of nine major coastal cities built on deltas - all of them considered vulnerable to extreme weather and flooding, according to a study published in August by scientists from Leeds University and the Netherlands, supported by UNESCO and the Dutch government.
The study used a new measure called the Coastal City Flood Vulnerability Index, which looks at many factors, not only a city's physical exposure, hydro-geological factors, hardware and infrastructure, but also social, economic, political and administrative factors.
It considers the degree of unregulated coastal development, economic output and resilience, rapid urban development, people's proximity to water, ease of evacuation, the age of the population (older people being more vulnerable than young), disabled population, poverty, number of shelters and so on.
Researchers said risks come from Shanghai's physical exposure due to a long coastline and a large volume of water flowing through the city in the Huangpu River, Suzhou Creek and other smaller creeks. Moreover, although a large population lives in flood-prone areas, the city has invested less than its European counterparts in various forms of protection, it said.
"A once-in-100-years flood in Shanghai would lead to widespread damage, with serious consequences for the city, across China, and through wider economic links for the whole world," said one of the authors, Nigel Wright, from the University of Leed, in the report.
Improved drainage
The Shanghai authorities, cited earlier, rejected the report.
The water authority emphasized that the drainage system has been steadily improved over the years and work is ongoing. "The maintenance of underground drainage pipes is constant. Last year we maintained 8,000 kilometers of pipes and we're about to do more this year," said Zhuang Minjie, a deputy director of the drainage department of the water authority.
Flood-prone areas are checked before every flood season so repairs can be made and problems averted, he said. The department has also set up a citywide monitoring system to alert authorities when flooding reaches 20 centimeters.
The city has established 157 monitoring locations, including 125 at tunnels where flood waters collect, Zhuang said. "Once accumulation reaches 20 to 30 centimeters, the police will be alerted to decide whether to close the tunnel."
The city also has been increasing capacity with larger pipes. Drainage pipes on 14 roads will be renovated this year and 28 drainage systems for roads and neighborhoods will be established or renovated by 2015.
Unlike Beijing
However, the Shanghai Water Authority conceded that the city might not be able to cope if it suffers a downpour similar to that caused by Hurricane Sandy or the one that struck Beijing in July.
"Shanghai's capacity of 36 millimeters per hour does not mean 72 millimeters every two hours or 108 millimeters every three hours in key places," Zhuang said. "The capacity cannot be accumulated, since the drainage system might be overwhelmed after hours of rain." In some areas of Beijing the precipitation even reached 400 millimeters. "This is not about Beijing. I don't think any city could cope with that rainfall," he said.
He pointed out that very serious flooding might be averted in Shanghai because its geography is different from Beijing's.
"The western part of Beijing is higher than the eastern part, which is more likely to flood," Zhuang said. "Shanghai is more flat and flooding deeper than two meters is unlikely to occur."
This is the second and final part of an article by our reporters Zha Minjie and Ni Yinbin on the safety of densely populated Shanghai in the face of possible extreme weather.
Drainage is considered a city's "conscience," and a better indicator of sound planning than high-rise buildings.
Jiang Dahe, a professor at the UN Environment Program-Tongji Institute of Environment for Sustainable Development, said city management should "beware of the power of the nature and the damage it can do to big cities."
"The rainfall volume in Shanghai has gradually increased in the past 50 years and sudden and heavy torrents have been more frequent," says the latest report by Tongji University on climate change and the safety of the city's underground public facilities.
The current public drainage system can handle precipitation of 36 millimeters per hour once a year in most parts of the city, and 50 to 56 mm once every three to five years in key areas such as airports and important business areas.
Shortcomings
Underground structures such as subway entrances and passages are relatively better able to handle drainage problems than the rest of the city, on average. But there are shortcomings.
"The biggest problem is that facilities' design only considers the rainfall through entrances and ventilation," said Zhang Jing, a member of the Tongji report's research team. "It fails to calculate ground seepage or flood conditions."
According to the Intergovernmental Panel on Climate Change (IPCC), there is a consensus that extreme weather will occur to varying degrees in the near future because of greenhouse gases and global warming. Shanghai faces possible invasion of seawater during extreme weather, said Zhang from Tongji. In August alone, five typhoons threatened the city, a record number.
Shanghai was described as the most vulnerable of nine major coastal cities built on deltas - all of them considered vulnerable to extreme weather and flooding, according to a study published in August by scientists from Leeds University and the Netherlands, supported by UNESCO and the Dutch government.
The study used a new measure called the Coastal City Flood Vulnerability Index, which looks at many factors, not only a city's physical exposure, hydro-geological factors, hardware and infrastructure, but also social, economic, political and administrative factors.
It considers the degree of unregulated coastal development, economic output and resilience, rapid urban development, people's proximity to water, ease of evacuation, the age of the population (older people being more vulnerable than young), disabled population, poverty, number of shelters and so on.
Researchers said risks come from Shanghai's physical exposure due to a long coastline and a large volume of water flowing through the city in the Huangpu River, Suzhou Creek and other smaller creeks. Moreover, although a large population lives in flood-prone areas, the city has invested less than its European counterparts in various forms of protection, it said.
"A once-in-100-years flood in Shanghai would lead to widespread damage, with serious consequences for the city, across China, and through wider economic links for the whole world," said one of the authors, Nigel Wright, from the University of Leed, in the report.
Improved drainage
The Shanghai authorities, cited earlier, rejected the report.
The water authority emphasized that the drainage system has been steadily improved over the years and work is ongoing. "The maintenance of underground drainage pipes is constant. Last year we maintained 8,000 kilometers of pipes and we're about to do more this year," said Zhuang Minjie, a deputy director of the drainage department of the water authority.
Flood-prone areas are checked before every flood season so repairs can be made and problems averted, he said. The department has also set up a citywide monitoring system to alert authorities when flooding reaches 20 centimeters.
The city has established 157 monitoring locations, including 125 at tunnels where flood waters collect, Zhuang said. "Once accumulation reaches 20 to 30 centimeters, the police will be alerted to decide whether to close the tunnel."
The city also has been increasing capacity with larger pipes. Drainage pipes on 14 roads will be renovated this year and 28 drainage systems for roads and neighborhoods will be established or renovated by 2015.
Unlike Beijing
However, the Shanghai Water Authority conceded that the city might not be able to cope if it suffers a downpour similar to that caused by Hurricane Sandy or the one that struck Beijing in July.
"Shanghai's capacity of 36 millimeters per hour does not mean 72 millimeters every two hours or 108 millimeters every three hours in key places," Zhuang said. "The capacity cannot be accumulated, since the drainage system might be overwhelmed after hours of rain." In some areas of Beijing the precipitation even reached 400 millimeters. "This is not about Beijing. I don't think any city could cope with that rainfall," he said.
He pointed out that very serious flooding might be averted in Shanghai because its geography is different from Beijing's.
"The western part of Beijing is higher than the eastern part, which is more likely to flood," Zhuang said. "Shanghai is more flat and flooding deeper than two meters is unlikely to occur."
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