Rising Priorities – How Chinese ‘Sponge Cities’ are Addressing the Threat of Flooding

How Chinese Sponge Cities are Addressing the Threat of Flooding

The low-lying capital of China’s Hubei province is strategically situated at the point where the Yangtze river (Asia’s longest) and the Han river (the Yangtze’s longest tributary) join together.

Traditionally known as ‘the city of a hundred lakes’, Wuhan once played host to 127 bodies of water in its central area alone as late as the 80s, however this number rapidly plummeted to around the 30 remaining today as a result of the city’s lightning fast urbanisation in the subsequent years.

In a geographical area already prone to severe flooding and regular bouts of torrential monsoon rainfall, the risks posed to a city that’s quite literally beset by water risks from all angles – above, below and surrounding – are all very real indeed.

Combine these threats with a rapidly changing and increasingly unpredictable climate situation, and things only get worse.

With a population of more than 8,000,000 and rising, none of this is good news for the city of Wuhan.


A Natural Solution to a Natural Problem

Following heavy downpours and the flooding that followed a bout of particularly bad weather that hit the city in 2016, Wuhan was unsurprisingly left with a significant bill to settle, both in terms of the human cost (14 people died) and the financial one (economic damage was estimated at around 2.3 billion yuan).

As is so often the case when the urban landscape overtakes, and – in the case of Wuhan’s lakes – covers over the natural one that existed before, the ability for any naturally inherent self-balancing mechanisms to take the strain of adverse events are all but removed entirely.

In the case of the 2016 floods, the end-result of the decisions made by planners and urban designers decades earlier came home to roost at the cost of serious damage to physical infrastructure as well as loss of life when storm defences in the city were overwhelmed.

The UN estimates that by 2035, the population of Wuhan is likely to exceed 10 million and with shifts in climate promising anything but increased stability when it comes to local weather prospects, residents of the city are understandably anxious.

So what can be done to prepare cities like Wuhan for more of the same, and potentially, much worse in years to come?

Only a year before the 2016 floods afflicted the city, it had been named as one of China’s first pilot areas to be designated a ‘sponge city’ with the goal of finding natural and ecologically focused alternatives to urban drainage and water protection solutions.

The subsequent floods were of course, a catalyst for speeding up the implementation of the sponge city project and added a significant sense of urgency to finding alternative options for protection against an increasingly dangerous reality.

In the years which followed, this has meant the deployment of natural solutions to mitigating flood risk through the re-introduction of the natural features which were once so prominent in the city have now taken a priority position in policy.

When it comes to flood planning and defence infrastructure, the race to retrofit areas of the city to include natural ‘sponge’ features is now underway with significant areas of the urban landscape reverted to an increasingly natural state before ‘the next big one’ strikes again.

One such example of this major retrofitting project is Nanganqu Park to the east of the city, which includes a host of sponge features ranging from specifically designated rain gardens and grass swales to artificial ponds, wetland areas and permeable pavements – all with the shared goal of naturally diverting, absorbing and ultimately, handling large volumes of water when needed.

The main method employed by the systems at Nanganqu is fundamentally the same for all sponge sites in Wuhan and beyond – the absorption of  excess water and its subsequent storage for a controlled discharge into rivers or other similar bodies of water when high water levels and flooding risk have subsided.


Expanding the Scheme – The Rollout of Sponge Cities

Wuhan is not alone in the development of the sponge city scheme however, and while the city formed one of the initial 16 earmarked as pilot areas originally, China has now expanded the programme to cover 30 cities nationwide.

While the cities currently participating in the programme are required to ensure that 20% of urban land includes sponge features, the scaling up of the project sees this requirement rise to 80% coverage by 2030, a considerable undertaking for any city.

The financial reality of this requirement is likely to become an issue of increasing concern for local authorities responsible for implementing the actions to meet this ambitious target with subsidies from the national level only set aside until 2020.

In light of this, alongside the growing spectre of climate change, alternative avenues for funding will likely be needed to ensure the retrofitting goals of the sponge city movement can be met across the board.

The expanded remit of cities enrolled in the sponge city movement include bustling metropolitan areas such as Shanghai and other areas of massive predicted growth in the near future.

With this in mind, it’s likely that as the risks of major urban flooding and the need for alternative drainage solutions continues to move up the national agenda, the private sector will likely need to shoulder some of the financial responsibility in making sure that the impact of development doesn’t come at the cost of natural protection against increased flood activity.

Wherever the money comes from, two things remain certain, China’s population is becoming increasingly urban and the risk posed by serious floods is greater than ever.

In areas of high density, high population, and a worryingly high potential for catastrophic flooding in the coming years, the steps taken by cities like Wuhan and others in China today in their adoption of ecological alternatives to flood resilience are being watching with a lot of interest internationally.

As mother nature becomes less forgiving and humanity becomes ever more urbanised, the results and overall impact of China’s sponge city experiment may have an effect far beyond national borders as other cities around the world begin to seek solutions to the same environmental problems.