As climate warms, ‘sponge cities’ may be China’s answer
To cushion the impact of extreme weather due to climate change, a Chinese landscape architect has been making the case for China and other countries to create so-called ‘‘sponge cities.’’
Yu Kongjian uses sweeping language to express his vision for cities that can withstand variable temperatures, drought and heavy rainfall.
The challenges for implementing this vision at a time of ambitious economic development in China are multifold.
Yu criticises much of Asia’s modern infrastructure for being built on ideas imported from Europe, which he says are ill-fitted to the monsoon climate over much of the Asian continent.
He points to recent floods that have wreaked havoc in many Asian cities, which he says are caused by this architectural mismatch.
‘‘There’s no resilience at all,’’ Yu says of the concrete and steel infrastructure of major cities, and of using pipes and channels to funnel away water.
‘‘Those are useless, they will fail and continue to fail.’’
Instead, Yu proposes using natural resources, or ‘‘green infrastructure’’ to create water-resilient cities.
It’s part of a global shift among landscape design and civil engineering professionals toward working more in concert with the natural environment. By creating large spaces to hold water in city centres – such as parks and ponds – stormwater can be retained on site, helping to prevent floods, he says.
Sponge infrastructure also, in theory, offers ways for water to seep down and recharge groundwater for times of drought. ‘‘The idea of a sponge city is to recover, give water more space,’’ Yu says.
A turning point in China’s awareness of climate change and urban adaptation came a decade ago, Yu says.
A devastating flood hit the capital, Beijing, July 2012. The city’s biggest downpour in 61 years overwhelmed drainage systems, swamped downtown underpasses, and sent flash floods roiling through the city’s outskirts. At least 77 people died.
Yu at the time sent a letter to Beijing’s party secretary, Guo Jinlong, calling for a change in how the government approaches city infrastructure. He continued to send letters to high-ranking officials and top leadership, including China’s leader Xi Jinping.
At a government working conference the next year, China incorporated the idea of sponge cities as a national strategy, ‘‘giving full play to the absorption, storage and slow release of rainwater by ecological systems’’.
In 2014, the central government issued a directive: recycle 70% of rainwater runoff in 20% of urban areas by 2020, and in 80% of such areas by 2030.
The following year, it launched 16 pilot sponge city projects, adding 14 more in 2016, with funding each year for three years.
The top-down mandate and subsidies spurred a boom in waterabsorbing infrastructure, including in large cities including Beijing, Shanghai and Shenzhen.
Cities around the world are similarly trying to integrate ‘‘bioswales’’ along the sides of roads, protect remaining marsh areas to absorb water, and increase the capture of roof rainwater.
An experiment under way
In China, one demonstration park is located in the northeast corner of the city of Nanchang in southern China.
In mid-October, engineers put the finishing touches on a lush, picturesque 50ha park designed to cushion the impact of both floods and droughts.
Formerly a coal ash dump site, the ‘‘Fish Tail’’ sponge park is built in a low-lying section of the city, and is intended to regulate water for surrounding neighbourhoods and business districts.
The fly ash, a byproduct of coal combustion, was mixed with soil to create mini-islands in the lake that allow water to permeate. Fang says the mixture, held in place by plant roots, prevents the ash from flowing into the water.
During dry periods, the water can be withdrawn, purified and used for plant irrigation.
Fang Yuan, an engineer at Yu’s design institute, Turenscape, says the park serves as ‘‘an ecological aquarium,’’ capable of retaining 1 million m3 of water during floods, and means the water can be used, instead of just discharging it into the sewerage system.
The park also serves as a habitat for plants and wildlife disrupted by extreme weather such as drought.
An uncertain future
At times, the sponge city concept has been difficult to implement in China. Misallocation of funds, lack of expertise in sponge city planning, and other snags have doomed some projects.
In April, the Ministry of Housing and Urban-Rural Development announced that some cities had ‘‘insufficient awareness, inaccurate understanding, and unsystematic implementation of sponge city construction’’.
The notice also warned against using funds earmarked for sponge city construction for other general infrastructure projects, such as buildings and roads.
Those guidelines were issued after massive rainfall and catastrophic floods in the city of Zhengzhou killed 398 people last year. Floodwaters inundated a section of the city’s subway, trapping hundreds of commuters. Rescuers flocked to the scene, but 14 people died in the subway disaster.
Notably, Zhengzhou was one of the pilot sponge cities. Some questioned whether sponge city projects worked at all.
But an investigation by the State Council, released in January, found that billions of yuan in funds had been misspent. Only 32% of the money that was invested went to what the government defined as sponge city concepts.
‘‘Even at the critical moment when the whole country mobilised forces to support Zhengzhou’s rescue and disaster relief, they were still ‘building flower beds’,’’ the State Council report said.
Yu acknowledges that there is an oversight problem. ‘‘Many of the cities just use it as propaganda – just to get a lot of money from the central government,’’ but then invest the funds in other projects, he says.
Biggest lake vulnerable
While the problems involved in implementing absorptive cities are being worked out, China’s vulnerability to extreme weather is clear.
A prolonged drought since July has dramatically shrunk China’s biggest freshwater lake, Poyang. In the village of Tangtou, on the lake’s normally water-blessed northeast corner, residents are scooping buckets of water from a village pond to tend their vegetables.
Villagers say they’ve hardly seen any rainfall since July, let alone water in their corner of the lake.
‘‘The whole lake was completely dry, and even the Yangtze River was dry,’’ said 73-year-old Duan Yunzhen as he scattered pond water on to his crops.
‘‘We planted rice, cotton, sesame, and sweet potato – they are all suffering from drought,’’ said 62-year-old Hong Zuhua.