WORLD FOCUS : Urban Asia

'Sponge cities' the solution to China's flooding woes

The urban population in the Asia-Pacific region has grown over the last three decades to more than a billion people, and by 2040, it is expected to add another billion to its numbers. By next year, half of the region's population will live in cities. The Straits Times presents a new series highlighting Asian cities and ways to tackle pressing urban issues. This third instalment looks at how the Chinese city of Wuhan is transforming itself into a 'sponge city' to deal with floods.

When Wuhan, the capital city of central Hubei province, was hit by torrential rain in July last year, hundreds of roads became impassable.

Subway stations were flooded, and the Xinhua Road football stadium - built in the 1950s - looked more like a giant swimming pool.

The city, which has a population of about 10 million people, sits at the confluence of the Yangtze and Han rivers.

During the heavy rains last year, it received a record 600mm of rain in a week - the amount of rain the whole of Australia gets in a year.

Wuhan resident Wang Haibo, 37, said the newer parts of the city, in the Nanhu and Tangxunhu areas, were the most affected. Many of the houses there were built very rapidly over the last few years.

Ms Wang, a sales and marketing executive, said: "Clearly, the drainage system could not keep up.

Netizens made jokes, saying Wuhan residents could "enjoy a view of the sea" - despite the city being hundreds of kilometres from the coast - and that newly-weds will now need a house, a car and a boat to start their new lives.

Wuhan has a population of about 10 million people. During the heavy rains last year, it received a record 600mm of rain in a week - the amount of rain the whole of Australia gets in a year. ST PHOTO: CHONG KOH PING

Wuhan, the capital city of central Hubei province, sits on the confluence of the Han and Yangtze rivers. It receives the bulk of its annual 1,300mm rainfall during the summer months, between June and September, making it highly prone to flooding. ST PHOTO: CHONG KOH PING

  • 180

  • Number of Chinese cities that have suffered floods between 2012 and 2015.


    Number of people affected in 24 provinces in the first half of this year by heavy rains and floods.


    Number of urban Asians at risk of inland flooding by 2025.

  • No more wet shoes on rainy days

  • They raised their voices and even their hands as they tried to stop workers from digging up and replacing the pavement tiles in the common areas of their estate.

    The residents of Wugang Garden 123 felt irritated by the inconvenience arising from the works.

    Six months later, though, most of the estate's 6,000 residents, all current or former workers of steel mill giant Wuhan Iron and Steel, or Wugang in short, have forgotten about the heat, dust and noise.

    Instead, many said their "level of happiness" has gone up since the 11 million yuan (S$2.3 million) makeover was completed.

    Much has been done to ensure that downpours would not dampen their spirits - previously water-resistant roads and pavements have been replaced with permeable materials, which absorbs rainwater.

    Trees, shrubs and grass verges are planted all around to improve drainage. The underground drainage system was reworked to separate rainwater and wastewater so that the water directed to the rivers is not polluted, said Mr Yang Shengwen, project manager of the construction works.

    Long-time resident Lei Xiaolan, 65, said: "Our living environment has become prettier. The broken and uneven tiles on pavements are gone. And we now have nice courtyards where we can play badminton, dance and practice taiji. There aren't any more unsightly puddles all over the place when it rains so we don't slip and fall that easily."

    Retiree Liao Darong, 67, saw no need to dig up the pavement tiles initially. While the refurbishment was paid for by the government, he thought then: "This is simply a waste of money and creates a lot of inconvenience to the residents."

    But six months on, he is very pleased with the new permeable tiles - which feels and looks like the synthetic rubber tracks in the stadium - and the greenery that covers the once-barren grounds. "Now whether it's a drizzle or heavy rain, my shoes don't get wet," he said.

    Chong Koh Ping

Rapid urban migration and development are a major cause of urban flooding in Chinese cities each year, especially during the summer months.

As many as 180 cities across the country suffered similar floods between 2012 and 2015. In the first half of this year, heavy rain and floods affected 17.7 million people in 24 provinces, causing 134 deaths, destroying 24,000 homes, and resulting in a direct economic loss of 29.3 billion yuan (S$6 billion).

The picture is equally grim in other Asian countries, where hastily built urban areas are equally prone to massive flooding.

In South Asia, more than 1,400 people were killed in India, Bangladesh and Nepal, and millions were made homeless between June and September this year, in one of the region's worst flooding disasters in a decade.

And in Vietnam, lax policing over construction projects in new urban areas is being blamed for its flooding woes. Nowadays, during heavy downpours lasting two to three hours, many roads in Hanoi become "rivers", said former deputy minister of construction Pham Sy Liem recently.

He added that developers flouted building regulations and ignored the need for proper drainage systems, for the sake of profits.

This has led to more serious flooding in the new residential areas outside the capital Hanoi, compared with the Old Quarter in the city, which was built about a century ago.

According to a study commissioned by the Asian Development Bank in 2012, about 245 million urban Asians were at risk of inland flooding in 2010, and this number is likely to reach 341 million by 2025.

Water resources engineering expert Zhang Xiang, from Wuhan University, said: "As more people move into the cities, the forests, grass patches, ponds and lakes are replaced by roads and buildings.

"Gone is the natural green infrastructure that could absorb rainwater or slow the flow of water into the drainage system. On concrete and asphalt grounds, the rainfall becomes surface run-off, and the speed of flow is much faster.

"When that happens, the rapid build-up of water simply overwhelms the pumping stations, which can't work fast enough to release water into the rivers or lakes."

Flooding in the southern Chinese cities during the summer has become almost commonplace.

And the problem is spreading. Even arid Beijing in the north was hit by a flash flood in July 2012, in which 79 people died.

In a bid to solve the problem, Chinese President Xi Jinping in December 2013 said cities should be built like "sponges" to soak up 70 per cent of rainwater. Concrete surfaces were to be replaced by permeable materials and green spaces such as rain gardens to absorb and filter rainfall.

In one of the sponge city projects in Wuhan, pavements have been rebuilt with permeable materials, which will absorb rain water and leave the surface dry, even during heavy rain. ST PHOTO: CHONG KOH PING

Drainage systems were to be rebuilt to separate wastewater from rainwater, and to be stored and re-used for cleaning the streets, watering plants and even firefighting.

The initiative was inspired by green development concepts, such as low-impact development in the United States, and other similar initiatives in Britain, Australia and Singapore.

In 2015, Wuhan was selected as one of the scheme's first batch of 16 pilot cities. As a provincial capital, it receives a yearly grant of five billion yuan from the central government for three years.

In return, it was required to upgrade 20 per cent of its urban areas to "sponge city" standards by 2020, and reach 80 per cent by 2030.

So far, the city has rolled out 288 projects to re-work roads, residential neighbourhoods, schools, parks and the drainage system in two pilot districts, with a planned investment of 110 billion yuan, said Mr Chen Yaowu, director of the engineering department of Wuhan Urban and Rural Construction Commission.

By April next year, two pilot districts, totalling about 40 sq km, are slated to be transformed into sponge cities. But a lack of awareness about the scheme has meant that not all residents are eager to see the plan rolled out in their estate.

To get residents on board, the city governments have been trying to cater to requests such as the building of extra parking lots and other amenities, while implementing upgrading works.

Since Wuhan was selected as one of the sponge city scheme's first batch of 16 pilot cities, new drains have been built and the underground drainage system upgraded to enable it to separate waste water from rainwater. ST PHOTO: CHONG KOH PING

Ms Kang Dan, head of the Wuhan Sponge City Research Institute, said there needs to be better coordination between city departments.

Urban and water management experts Asit K. Biswas and Kris Hartley, in a recent article, wrote that while China has a chance to lead the world in urban sustainability through the sponge city initiative, it faces the dual challenge of financial constraints and a "lack of expertise of local governments to effectively coordinate and integrate such a complex set of activities".

What China can do, they said, is to improve regulatory enforcement and try and attract private investment .

However, it is early days still in the rollout of the sponge city concept, Ms Kang said. The works in the pilot districts make up only 7 per cent of the 600 sq km of the urban areas in Wuhan, she added.

She said: "For now, it is a political project driven by the top local leader, a mayor's project. Lots of manpower, resources, energy and money are being poured into it."

But it remains to be seen how it will be introduced to other parts of the city, and how the concept can integrated with new reconstruction projects, she added.

Another question is whether the private sector will be involved, she said.

Ms Kang said: "For thousands of years, we used to think about keeping water under control, keeping it at bay (zhishui). This concept of trying to manage rainwater is new to China's idea of urbanisation."

A version of this article appeared in the print edition of The Straits Times on November 14, 2017, with the headline ''Sponge cities' the solution to China's flooding woes'. Subscribe