Soak it up: China’s ambitious plan to solve urban flooding with ‘sponge cities’

Can the might of the Chinese government overcome complex needs and investor disinterest to deliver an ambitious programme to save China’s 450 million urban inhabitants from floods?Flooding causes more economic, social and humanitarian damage than any other natural disaster and has affected 2.3 billion people over the past 20 years, according to research from the Global Resilience Partnership. China has been particularly affected. This year saw the worst floods in the country since 1998. In July 150 people were killed in central and northern China after intense rainfall.“In China the climate is bringing more rain in summer. From June to September there will be high density rainfall which is bringing up urban planning problems,” says Michael Zhao, an associate and expert in water management in the Shanghai office of global urban designers Arup.“There’s already been very serious flooding for four or five years each summer. You will see flooding in more and more cities. As urbanisation brings more people to those cities the problem becomes worse and worse.”

An unprecedented scale

In December 2013 President Xi Jiping announced a national plan to combat flooding in China’s cities”“ inhabited by 450 million people. “He said that during the upgrade of urban drainage infrastructure they should make it a priority to retain valuable water resources and to utilise the natural system to achieve drainage, to establish natural retention, natural infiltration and natural purification ”“ like a sponge city,” says Zhao.Initially 16 cities were selected as pilots for China’s “sponge cities” programme, but eventually it will be rolled out nationally. Designers will concede to the wisdom of nature to ensure water is absorbed when there’s an excess: instead of water-resistant concrete, permeable materials and green spaces will be used to soak up rainfall, and rivers and streams will be interconnected so that water can flow away from flooded areas.The ambitious project is being funded by central government (15-20%), local government and the private sector. The central government is giving each city 400m yuan (£46m) a year for the first three years. In return, 20% of the chosen cities must be constructed to a sponge city standard by 2020, and 80% by 2030. All of the pilot cities need to have completed the pilot area construction by 2017.The sponge city programme takes inspiration from low impact development in the US, water sensitive urban design in Australia and sustainable drainage systems in the UK.But nothing at this scale has ever been attempted before. “The sponge city programme is more comprehensive and ambitious,” says WenMei Ha, head of the China water management team at Arcadis, an international urban consultancy which was appointed to this plan by the government.Arcadis is working on a sponge city project in Wuhan, a city of 10 million people in Hubei province in central China. The city is in dire need of efforts to counter the risk of flooding ”“ in July, metro stations, roads and the football stadium were all under water.“Generally, this programme involves water governance, financing structures and technical measures,” Ha says. “With regard to the technical aspects, an integrated urban water system would be built, which incorporates low impact development measures, upgrades the traditional urban drainage system and provides solutions for excessive run-off discharge. These three measures together make up a sponge city storm-water system.”

The sponge cities programme isn’t just designed to tackle flooding but also to offer a solution to water shortages. China has much less freshwater per capita than most countries, many sources of what are polluted. Arup is working on a sponge city masterplan in Baotou in inner Mongolia.“Water shortage is seriously heightened there,” says Zhao. “Urbanisation is quite limited by the shortage of water.” The plan looks at how to retain rainwater and keep it inside the catchment. Although flooding is not a problem in Baotou now, urbanisation is happening rapidly and “we can foresee [that] if it continues in the conventional way, urban flooding will heighten in the next five years,” he adds.

Measuring progress

It’s two years since the sponge cities programme began but Ha says it’s still too early to tell if it will be successful. The programme is facing great challenges due to “the ever increasing urban population,” he says. “One of the biggest take aways for urban planners and policymakers in other countries would be how to overcome those challenges and integrate a climate resilient system into urban planning.”Zhao agrees that the programme is “very challenging”. He says, “from our experience working with pilot cities governments and local design institutes, there are both technical and management issues, depending on how the local pilot cities manage those challenges; some cities move faster, some comparably slow.” The technical challenges are making sure that the masterplans accurately consider the local hydrology and climate, Zhao adds.And there are challenges around financing the project by public private partnership (PPP) investment, due to the need to identify the returns for all parties. “Because it is difficult to measure the service, it is difficult to set up a healthy financial model,” says Zhao. “The rainwater treatment facilities owners [for example] don’t normally benefit [financially].” But he says that once a successful PPP agreement is decided upon, that can be used in other cities.The Economist recently reported that investors are “not interested” in the sponge city programme, indicating a slowdown of the Chinese economy in general. But if the majority of China’s densely populated cities are submerged every summer, the economy and the residents will suffer even more.Still, Zhao sees the sponge cities programme as “a very positive change. Previously in the past 30 years people just followed conventional national standards ”¦ We are shifting to a sustainable way to manage water issues in cities. It’s a good sign.”Talk to us on Twitter via @Guardianpublic and sign up for your free weekly Guardian Public Leaders newsletter with news and analysis sent direct to you every Thursday.