China is reusing rainwater with ‘sponge cities’

By Professor Asit Biswas

China’s high-profile fight with urban flooding has flooded – so to speak – international headlines more and more often recently. But the nation is not the only one struggling with flooding.

As more and more people take up residence in cities and the metropolises themselves fight to keep up with the rapid urban migration, land development is slowly creeping into areas prone to flooding.

For example, the recent flood Mumbai, India dealt with was due in part to the unregulated and quick development of wetlands – rampant in Bangladesh and Nepal as well. Similarly, a severe flood in Beijing, China, in 2012, caused widespread panic in the city’s transportation system, and more recently in 2016, drainage systems in Nanjing, Tianjin, and Wuhan were overwhelmed by flooding.

This year, floods in the United States (U.S.), consequences of a series of hurricanes, have underlined the many risks present when developing land located in low-lying and environmentally sensitive areas.

Over-extraction of groundwater, aging waterways and infrastructure, and urban flooding are the main drivers behind China’s recent push to address a vicious cycle. Unchecked urban development and heavy use of impenetrable material such as concrete block soil from taking in rainwater, and result in further investment in infrastructure that more often than not, continue impeding natural processes and simply worsen flooding.

Thus, China’s “sponge city initiative” is specifically targeted at stopping this cycle through the utilisation of permeable surfaces and green infrastructure. Unfortunately, the initiative is currently facing two hurdles: Financial limitations, and a dearth of expertise on the part of local governments to coordinate and integrate the complex and complicated activities.


Engineering solutions are popular, but metropolises, while advanced, ae unable to very simply pipe risks of flooding away.

China’s answer to flooding was not only innovative, it is ambitious. Debuted in 2015 in 16 cities across the nation, the project aims to reduce rainwater intensity by improving and distributing absorption capabilities more evenly across selected areas. By 2020, China wants 80 per cent of its urban areas to be able to absorb and reuse at least 70 per cent of rainwater, replenishing groundwater supplies and increasing water supply security while also lowering the chance of flooding. A collaborative effort, the responsibility is shared among city regulators, engineers, and property owners.

The project shares a number of similarities with North America’s low-impact development (LID), which copies natural processes to safeguard the quality of water, according to the U.S. Environmental Protection Agency (EPA).

Metropolises in China – both existing and in the works – are making efforts and pledging to expand the plant coverage in urban areas. In 2016m Shanghai disclosed the construction of some 400,000sqm of rooftop gardens.

Lingang, a city in Pudong, Shanghai, that is in the pipeline, is a sponge city typical of these measures, including scenic wetlands to collect rainwater, rooftops blanketed with greenery, and absorbent pavements to hold excess water and enables evaporation to moderate the temperature. Projects in Xiamen and Wuhan have already performed well, holding their own in the face of heavy rainfall.

Sponge city initiatives, however, need efforts that are comprehensive, integrated, and sustained, including effective environmental governance. Selective enforcement and weak regulations can spell the end of the project, and while keeping a firm grip on controls is more tedious and far less exciting than the boldness and dynamism of innovation, it is vital for water management.

Funding is another challenge sponge cities face. Although an estimated US$12 billion have already been spent on sponge cities in total, central governments only bankroll an approximate 15 to 20 per cent of the amount, with the remainder taken up by the private sector and local governments.

Perhaps more lamentably, the sponge city initiative has come up in a time of rising municipal debt crises driven by cut bond ratings, and fidgety bond markets, and limited financial reforms. The project may begin to discover that borrowing costs are higher, and avenues to lowering debt, smaller and narrower.

Even worse, it is becoming more difficult to pitch investment in sponge cities, with unattractive tax incentives, low transparency and high-credit markets resulting in mild interest from prospective investors who are in a market saturated with various other investment options.

And until the initiative can gain the traction it needs, it will have to come up against more familiar and visible competitors, such as utilities and roads.

Innovative water initiatives may have been adopted around the world, including flushing systems with water collected from rooftops, wetland restoration, flexible water retention, and bioswales, but until interest in it is properly revived, there are not many steps the sponge city initiative can take.


Source: Eco-Business