A floating forest from a densely populated city in China, Nanchang, has recently gone viral for its breathtaking views. Comprising native fauna, flora, and volcanic rocks mimicking a natural forest, this urban park lies on 137 acres of urban land. [1] This is known as a sponge city. It is an initiative the Chinese government took in response to urban flooding, stormwater regulation, and preservation of biodiversity. So what does it mean for cities to become ‘spongy’? 

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Aerial view of Sponge park at Nanchang_©www.greenroofs.com

Like everywhere else, even in China, urbanisation and industrialization have led to rapid economic and urban growth. These come at the cost of climate change, threatening human life, entire ecosystems, and nature. Extreme weather events may lead to frequent flooding, increasing cyclones, landslides, droughts, and desertification. [2] Urban development such as the construction of roads, buildings, and structures often results in impermeable surfaces contributing to flooding. This runoff is characterised by high velocity, amplifying peak flow while reducing natural groundwater replenishment due to no percolation and evapotranspiration. 

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Urbanisation rate in China_©news.cgtn.com

Furthermore, these human activities produce greenhouse gases, of which half remain in the atmosphere while the other half are absorbed by land and ocean. Cities play a complicated role in the climate crisis, especially in maintaining biodiversity. As urban expansion continues it can drive habitat loss that directly puts some species in danger, profoundly impacting global biodiversity. Biodiversity or biological diversity is the variety of life on Earth, from bacteria to entire ecosystems like forests and coral reefs. And, the ecosystems these biodiversities contain have natural carbon sinks. This is why biodiversity is our strongest natural defence against climate change. [4] Dr. Charlie Nilon, Professor of Urban Wildlife Ecology and Conservation at the University of Missouri says, ‘The vital thing to think about is not so much how urbanisation reduces biodiversity, but really how in cities you can conserve biodiversity’ One of the best ways to do this is by creating environments where nature can flourish. Environments where excess water can be soaked up. [1]

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Terraced wetlands in Haikou_©sreasonstobecheerful.world

This is where sponge cities come in. The Ministry of Housing and Urban-Rural Development of China launched The National Sponge City Pilot Program in 30 cities nationwide in 2015. They aimed to green the grey, which is done by supplementing existing (‘grey’) infrastructure that relies on concrete pipes and dams with natural solutions (‘green’) like gardens that are designed to capture rains and native trees that suck up excess water through their roots. [5]

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Location of pilot sponge cities_©www.mdpi.com

Sponge cities offer several benefits, including:

  • Better coping with floods
  • Improved underground water quality 
  • Enhanced biodiversity

This is drawn from the ancient Chinese drainage system because, for centuries, Chinese cities handled water well partly because they were designed by keeping nature in mind. Sloping roofs were used to help rainwater drain off to the permeable pavement further leading to the water reservoirs, and walls were lined with flower beds to soak up excess water. [1]

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Drainage systems in ancient southern and northern China_©www.mdpi.com

Today natural solutions like these have been reimplemented across different cities in China. For example, in Qian’an, a sewage pipe was replaced by a natural infiltration system that uses vegetation beds to purify rain and stormwater. In Shanghai, concrete roads were replaced by permeable pavements to increase stormwater percolation, which further recharges groundwater. [1]

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Haikou Meishe River – before and after shots of the ‘sponge city’ hotspot_©www.euronews.com

And Nanchang’s fishtail sponge park is inspired by the ancient concept of farming atop marshland, and by simple cut-and-fill techniques such as the Aztec Chinampas, or floating garden system, the coal ash dumped on site was recycled, and mixed with dirt from the fish pond dykes to create numerous islets. Along with this, a lake that could accommodate 2 metres of water rise, providing the capacity to catch a full 1 million cubic metres of stormwater inflow was provided. Most of these projects rely on introducing native flora on urban land to soak up excess stormwater. Which has turned out to be a great way to handle urban floods which indeed supports biodiversity. [3]

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View of the fishtail sponge park at Nanchang_©www.greenroofs.com
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Details of the fishtail sponge park at Nanchang_©www.greenroofs.com
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View of islets at the fishtail sponge park at Nanchang_©www.greenroofs.com

Despite these benefits, these spongy cities can only handle excess water up to a certain point. 

In 2021, in Zhengzhou, a historic flood drenched the city and drowned the sponge city with it. And they have other limitations as well. Such as national standards and codes for sponge cities are difficult to enforce, the standards are too general, and different cities have different socio-economic status, climate, and hydrology. Plus, sponge cities require a lot of space and have huge budgets. [1] Therefore, what might work in one city won’t work in others. 

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Yanweizhou Park in Jinhua City_©www.scientificamerican.com

Of course, one type of city design is not the solution to the climate crisis or will save us from it but it can certainly make a difference in how we live with it.

Citations

  1. ‌www.youtube.com. (n.d.). How China is designing flood-resistant cities. [online] Available at: https://www.youtube.com/watch?v=nf-Yy3EuZi0.
  2. ADB BRIEFS NO. 222. (n.d.). doi:https://doi.org/10.22617/BRF220416-2.
  3. Greenroofs.com. (n.d.). Nanchang Fish Tail Sponge Park. [online] Available at: https://www.greenroofs.com/projects/nanchang-fish-tail-sponge-park/#:~:text=In%20the%20city%20of%20Nanchang [Accessed 2 June. 2024].
  4. ‌United Nations (2022). Biodiversity – Our Strongest Natural Defense against Climate Change. [online] United Nations. Available at: https://www.un.org/en/climatechange/science/climate-issues/biodiversity.
  1. Jenkins, M. (2020). Sponge City. [online] LILP. Available at: https://www.lincolninst.edu/publications/articles/sponge-city-shenzhen-explores-benefits-designing-with-nature.
Author

Transitioning from architecture to UX design, she juggles a medley of passions: designing, writing, and training in MMA. Her fixation lies in crafting meaningful, aesthetically pleasing, and user-friendly experiences. Balancing creativity with functionality, she navigates this diverse landscape with fervor and a relentless pursuit of beauty and utility.