Sponge city soaks up rainfall to boost climate resiliency

Location: Zhenjiang, Jiangsu, China

Population: 1,200,760 (urban area)

Climate: Subtropical monsoon

Duration: 2015 – 2037 (assuming the 23-year lifespan of the project)

Sector: Water efficiency

Funding sources: Public-private

City networks: C40

Savings: N/A

Solutions:  The Sponge City project is aimed to capture and release rainwater while also reducing pollution.

Multiple benefits: Increasing Zhenjiang’s resilience to flooding and extreme weather occurrences makes it a safer place to invest for businesses and inhabitants.

With the Yangtze River to the north, mountains to the south, and smaller rivers interlacing its boundaries, the City of Zhenjiang is at a high risk of flooding.

Objective – To soak up rainfall via the Sponge City project.

Solutions – Faced with the vast difficulty of urban flooding, China’s national government is promoting the Sponge City concept to assist cities in capturing rainwater and improving their resilience to climate change. Zhenjiang has accepted the initiative, requiring that every relevant new project launched after October 2015 adhere to the Sponge City standards. As a result, to secure finances for future initiatives, the municipality formed a management mechanism and office to encourage Sponge City development. So far, the city has deployed projects totalling around 19 km2 in size, focusing on one lake and three rivers.

The project establishes a plan for intercepting wastewater discharge, purifying rainfall, and protecting waterway health. An investigation was performed to identify the sources of various contaminants, devise a strategy for reducing them, and calculate how much wastewater can be discharged based on the Total Maximum Daily Load. The Sponge City project will also preserve local water bodies such as the Yangtze River from contamination by isolating wastewater and stormwater infrastructure and ensuring wastewater is treated before discharge.

Funding – The city has raised about $200 million through public-private partnerships, utilizing throughout the project’s 23-year lifespan. The project will require around $62 million in financing, with the government owning 30% of the stock and the private partners holding 70%. The enterprises participating in Sponge City serve the Zhenjiang projects and ten more throughout China.

Innovation – N/A

Success factors – 1) Spongify your city: The Sponge City concept is rapidly gaining traction in Chinese cities and with reason. Urbanization lowers permeable surfaces, exacerbating the risk of flooding. When cities are planned with rainwater penetration in mind, resilience is increased. Permeable pavements and naturalized areas absorb water; they also recharge groundwater and reuse greywater during the dry season. 2) Leverage Public-Private Partnerships. Public-private cooperation with Sponge City industrial partners is expected to strengthen the local economy and create jobs.

Significant outcomes:

• Zhenjiang’s urban areas will be completely compliant with Sponge City standards by 2025;
• Reducing pollution in local waterways increased the opportunity for biodiversity to thrive;

Greener cities also help mitigate the urban heat island effect, which creates a cooling microclimate during heatwaves.

Synergies with local policies:

• Regulations of Zhejiang province on the protection of drinking water sources. These Regulations seek to increase the protection of drinking water sources, improve drinking water quality, assure its safety, safeguard public health and safety, and promote collaborative and sustainable economic and social development in Zhejiang province.

Political alignment:

• China’s Nationally Determined Contribution (2016). It is targeted toward strengthening resilience. The key topics emphasized are the conservation and efficient use of water resources. The flood protection and disaster reduction system has been optimized to maximize the capacity to withstand and recover from floods;
• 14th Five-Year Plan period (2021–2025). The Plan is comprehensive in scope and targets each of the three pillars of development – economic, social, and environmental (source). Additionally, one of the priorities is to bolster the development of water conservation () infrastructure (source).

Marketability: Yes. The concept of rainwater infiltration to improve resilience in cities can be widely extended to other cities with a risk of flooding, making good use of public-private partnerships.