viernes, 9 de marzo de 2018

China's sponge cities are turning streets freen to combat flooding

A small part of Shanghai is turning greener, street by street.
In the Lingang district, pavements are lined with trees, gardens and public squares full of plant beds. Between cranes and construction sites, plans display new buildings enveloped in the green and blue of parks, streams, and water features.
Lingang (also known as Nanhui after it was renamed in 2012) has a mission. As Shanghai’s “sponge city”, it is piloting an ecologically friendly alternative to traditional flood defences and drainage systems in the coastal city which faces long-term risks from rising sea levels.
Rapid concrete development in China has often blocked the natural flow of water with hard, impervious surfaces; to reverse this, the sponge city concept focuses on green infrastructure, such as wetland areas, rooftop plants and rain gardens.
“In the natural environment, most precipitation infiltrates the ground or is received by surface water, but this is disrupted when there are large-scale hard pavements,” says Wen Mei Dubbelaar, director of water management China at Arcadis. “Now, only about 20-30% of rainwater infiltrates the ground in urban areas, so it breaks the natural water circulation and causes waterlogging and surface water pollution.”
In Lingang, the wide streets are built with permeable pavements, allowing water to drain to the soil. Central reservations are used as rain gardens, filled with soil and plants. The large manmade Dishui Lake helps control the flow of water, and buildings feature green rooftops and water tanks.
Since disastrous large-scale flooding in Beijing in 2012, flood prevention has rocketed up the state agenda. The Sponge City initiative was launched in 2015 with 16 “model sponge cities”, before being extended to 30, including Shanghai.
“The first thing is to try and preserve or restore natural waterways, because that is the natural way to reduce the flooding risk,” says Prof Hui Li at Tongji University. “In Wuhan, for example, the main problem is that a lot of small rivers were filled in during building. That is a benefit the Lingang area has, as there is still a lot of agricultural land and a manmade lake which has capacity to hold more water during heavy rain.
A satellite view of Lingang at the tip of the peninsula around 60 km south of Shanghai city centre. Credits: Landsat 5 and landsat 8/Nasa.
“In the past, humans have taken the land away from the water; now we need to give the land back.”
Lingang can introduce new innovations into its urban fabric, but retrofitting older areas in Shanghai is difficult. Recent redevelopments include the former industrial West Bund Riverside, using wetlands, permeable materials and raised walkways to make the area naturally “spongey”.
But it is difficult to create room for new green space. Even existing parks are largely a missed opportunity, says Li, usually built higher than street level and failing to offer a natural escape route for runoff floodwater. Most focus is on green roofs – the Shanghai government wants 400,000 sq metres of new rooftop gardens – or gradually replacing pavements.
By 2020, the government wants 20% of the built area of each pilot district to have sponge city functions, meaning at least 70% of stormwater runoff should be captured, reused, or absorbed by the ground. By 2030, a huge 80% of each city should meet this requirement.
This target puts pressure on new areas to compensate for older districts, where a wholescale retrofit by 2030 seems doubtful.
There are plenty of other challenges. The central government will only provide about a fifth of funding needed – the rest must be raised by cash-strapped local governments and often unenthusiastic private investors.
Academics have warned planning models are not specific enough to accommodate the vast differences in China’s geography, and there is a sharp learning curve to match new concepts with city practicalities. In Lingang, for example, crossing the road is difficult due to the large rain gardens in central reservations.
Nonetheless, urban planners say additional innovations have emerged from the process, including more sustainable design and relief for China’s water-starved regions by managing stored rainwater.
“Sponge city infrastructure is beneficial because it is also changing the living environment, helping with pollution and creating a better quality of life in these areas,” says Dubbelaar. “The initial driver for sponge cities was the extreme flooding of urban areas, but the change in mindset, that development should have a more holistic, sustainable approach, is an extra benefit that is evolving during this project.”
Lingang is clearly hoping its innovative greenery will bring tourists, with several hotel chains around the lake, a maritime museum and tourist information centre already open. One such visitor from the nearby suburbs says she is a fan of Lingang – she doesn’t know the term ‘sponge cities’, but she likes it.
“I like all the trees and parks,” she considers. “It doesn’t really feel much like a city. I think it’s much more pleasant than other parts of Shanghai.”

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Wetland areas help to absorb rainwater in Lingang. Photograph: Helen Roxburgh

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