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Circle Economy and ICLEI have partnered up to initiate the go to knowledge hub of case studies about the circular economy in cities. The Cities Collection is a repository of case studies that demonstrate the role of cities in the circular transition, and includes policies, business cases and research articles. Cases in the Collection flow into an ecosystem of digital products which support users in transitioning cities to circularity, for example [Ganbatte](https://ganbatte.world/cities/) and <a href="https://circulars.iclei.org/" target="_blank">ICLEI Circulars</a>, both part of the <a href="https://circulars.iclei.org/circle-lab-for-cities/" target = _blank">Circle Lab for Cities Programme.</a>




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Circular Cities

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The built environment sector largely exists to serve our universal need for shelter, and as such is one of the most important consumers of raw materials in the world.

We believe the built environment should be a ‘living’ system in which building materials and products are optimally used and reused— a system that operates within the boundaries of our planet, preserves the (business) value of its resources, and ensures the well-being of its inhabitants.

Tremendous opportunities to reverse the tide and prevent a state of lock-in from happening exist for regions where the built environment sector has yet to mature. There is also still hope for those regions where the fate of the construction sector may seem set in stone.

This is why two key strategies stand out: 

- Preventing lock-in through thoughtful design
- Optimising (material value) through transformative re-design

Built environment

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Starter Kit collection

Policy case

Impact on the availability of resources as well as their effect on living organisms, ecosystems, and components of the environment.

Ecological Impact

Impacts on the social fabric of the community and well-being of the individuals and families.

Social Impact

Impact on the health and happiness of human populations

Well-being

Reduced use and withdrawal of water and rate of recycling and reuse of water

Save Water (SDG6)

Societal Services

Providing public and private education and support services at any level or for any profession, and governmental and public administration services, including judicial, regulatory, and legislative activities, taxation, defence, public order and safety, immigration services, foreign affairs and the administration of government programmes

Education and Government Services

Providing water and sewage services, including water collection and distribution, water treatment systems and sewage treatment facilities

Water and Sewage

Water supply, sewerage, waste management and remediation activities

Ensure renewable, reusable, non-toxic resources are utilised as materials and energy in an efficient way

Prioritise regenerative resources

Replace freshwater with less impactful alternatives and enact water efficiency measures

Regenerative water

Replacing freshwater use with rainwater, fogwater, seawater, etc.

Alternative water use

Efficiency and effectiveness of water supply services must be secured by minimising the leaks, through a combination of leak detection techniques, pipes maintenance and reparation and water audits. Leak minimisation can be enhanced through the use of sensor technologies.

Minimise leaks

Measures to drain accumulating rainwater from rooftops, roads or other public surfaces and channel it into containers for multipurpose use. These include watering plants and crops, as an input into manufacturing processes, the establishment of public water features, or the introduction back into plumbing systems, Uses may include the application of filtration and treatment systems when needed. 

Manage rainwater

Greywater is drained water from bathing, laundering, washing dishes etc. and excludes sewage (black water). Greywater can be reused most commonly for irrigation and toilet flushing if the appropriate system to capture and distribute it is in place. To extend usage possibilities, filtration and treatment systems may be introduced. 

Use greywater

Locally produced food has to travel shorter, which means less fuel is consumed and less greenhouse gases are generated. Moreover, buying locally produced food helps local farmers and markets and creates more jobs in the local businesses. 


Produce locally

Other

'Manage' influences the use and function of physical and material elements within the urban environment. 

Manage

Infrastructure

Develop regenerative infrastructure

'Mobilise' sets the direction of and builds momentum towards long-term change, while also determining how this direction is determined and governed.

Mobilise

Visions and Ambitions

Roadmaps and strategies and targets

**Harmonize with nature** by promoting infrastructure, production systems and sourcing that allows natural ecosystems to thrive




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Regenerate

Use longer and more often by extending and intensifying use of existing resources, products, spaces and infrastructure

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Reuse

Do better with less by using and supporting infrastructure, processes and products that are designed to minimize material, water and energy use and waste generation from production to end of use


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Reduce

Prioritize solutions that use the power of functioning ecosystems as infrastructure to provide natural services to benefit society and the environment; consider nature-based replacements for grey infrastructure.

Promote solutions inspired and supported by nature

Maintain and repair city-owned spaces and infrastructure to increase longevity, and support opportunities for residents to do the same for privately owned items and property

Support reuse, repair, remanufacturing, maintenance of existing resources, products, spaces & infrastructure

Ensure that infrastructure and built assets in the city are designed and upgraded to be as resource-efficient as possible.

Design infrastructure and the built environment for resource efficiency

Governments

Water system refers to the water supply network for storing and supplying water for use by the community.

One of the greatest challenges of a city is to provide its inhabitants with safe, clean water from a limited fresh water supply. Improving the city’s water infrastructure efficiency, such as minimising leakages, reduces the strain put on the limited supply, which in turn, helps to ensure inhabitants gain access to clean and affordable water.

The water infrastructure of a city typically consists of components such as surface water diversions, wells, pumps, transmission pipes and canals, treatment and storage facilities, and distribution network elements (Burian et al.). Options for improving the efficiency of the system include investing in water loss reduction systems, creating and following a regular maintenance program, and better matching water supply and demand (Global Water Partnership).

Cities can improve the efficiency of their water system infrastructure by conducting a water audit, in which all water flows are traced and losses in the system are identified to map where the most efficiency improvements can be gained. Alongside this, asset management can be used to create a short-term and long-term strategy of investing in new equipment, refurbishing existing equipment and developing maintenance programmes to ensure infrastructure is as efficient as possible, and leaks are minimised. Such management programmes create financial transparency amongst all stakeholders and provide useful long-term planning for larger infrastructure changes (US EPA)

💧 Water Systems

Cities worldwide are facing significant water-related challenges, including urban water runoffs, flooding, reduced water quality and severe water scarcity—exacerbated by rapid urbanisation and more frequent extreme weather events. On top of this, urban water runoff continues to be a major cause of water pollution in urban areas, carrying trash, bacteria, and other pollutants through gutters and stormwater systems into local waterways, typically without treatment.

City governments can pursue a “sponge city” approach by redesigning the urban fabric and integrating blue and green infrastructure (BGI) (e.g. rain gardens, permeable pavements, storage ponds, etc.) along traditional grey infrastructure (e.g. pipe networks, storage tanks, flood walls). This can help to absorb, store, filter and purify these water flows, in turn replenishing aquifers, reducing the need for expanding grey water management and minimising flood risk, while also reducing the heat island effect. 

Cities can do so by, for example, integrating requirements for BGI into municipal urban planning rules for newly built up areas of city districts, industrial parks and development zones, and integrating sponge city building requirements into municipal urban planning rules. Then, local governments could also strengthen collaboration between all relevant stakeholders—from real estate developers to engineers, to water-utility organisations—to identify locally relevant opportunities for sponge cities. 


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💧  Blue and green infrastructure for sustainable urban drainage

One of the greatest challenges of a city is to provide its inhabitants with safe, clean water from a limited fresh water supply. Improving the city’s water infrastructure efficiency, such as minimising leakages, reduces the strain put on the limited supply, which in turn, helps to ensure inhabitants gain access to clean and affordable water.

The water infrastructure of a city typically consists of components such as surface water diversions, wells, pumps, transmission pipes and canals, treatment and storage facilities, and distribution network elements ([Burian et al.](https://www.sciencedirect.com/science/article/pii/B9780123847034005098)). Options for improving the efficiency of the system include investing in water loss reduction systems, creating and following a regular maintenance program, and better matching water supply and demand ([Global Water Partnership](http://www.cawater-info.net/policybriefs/pdf/tec_brief_4_water_efficiency.pdf)).

Cities can improve the efficiency of their water system infrastructure by conducting a water audit, in which all water flows are traced and losses in the system are identified to map where the most efficiency improvements can be gained. Alongside this, asset management can be used to create a short-term and long-term strategy of investing in new equipment, refurbishing existing equipment and developing maintenance programmes to ensure infrastructure is as efficient as possible, and leaks are minimised. Such management programmes create financial transparency amongst all stakeholders and provide useful long-term planning for larger infrastructure changes ([US EPA](https://www.epa.gov/sustainable-water-infrastructure/things-local-officials-should-do-sustainable-water-infrastructure)).

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💧  Improving water infrastructure efficiency

The water consumed by households must be of a sufficiently good quality to safely drink, bathe and clean with. However, the quality of water required for each of these needs differs significantly. For example, potable or drinking water must be of a higher quality than the water used to flush a toilet or irrigate a garden (so called “greywater”).  It is possible to significantly reduce our overall water consumption by using and reusing non-potable water sources for lower quality purposes—a strategy particularly relevant for drought-stressed cities.

Greywater reuse systems can be applied at household level to collect water from showers and baths, filter and treat it, and then recirculate it to flush toilets or irrigate gardens. Alternatively, a sports centre can collect greywater from showers and hand basins and process it to be used to irrigate an adjacent sports field or community garden.

Cities can encourage the uptake of greywater reuse systems through awareness campaigns, regulations and financial incentives. Awareness campaigns can show the potential environmental and financial benefits of installing greywater systems. Regulations can be in the form of building codes and requirements in which the installation of a grey water reuse system is compulsory, unless practically infeasible. Financial incentives are usually in the form of rebates for installing such a system. Municipal governments can also lead by example and procure such greywater reuse systems in municipal or city-run buildings, such as municipal offices or schools. This can not only improve the water-efficiency of such buildings, but can also showcase the benefits of the systems, and support local market demand.



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💧  Grey-water reuse systems

Regenerate strategies phase out hazardous or toxic materials and processes and substitute them with regenerative biomass resources. A circular economy aims to mimic natural cycles—by shifting to more regenerative farming practices, for example—while also maximising the share of circular biomass that enters the economy. Regeneration can happen both at the systems level (by designing regenerative processes) as well as at the product level (by switching synthetic to organic fertilisers, for example).

Impacts

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Industries

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A framework of policy instruments that enabled and encourage the transition to the circular economy

Policies

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A framework of policy instruments that enable and stimulate the transition to the circular economy

Nace Sectors

The principles of a circular economy concern designing out waste, regenerating ecosystems and keeping items in use. Decoupling the economy from material flows—improving the rate of resource productivity faster than the economic growth rate—is also a consistent guide. By evolving with the growing number of applications of circular economy principles, and consolidating these strategies across thematic areas, Circle Economy’s Key Elements Framework (KE) renders the elements of the circular economy salient and serves as a basis to derive contextual strategies and interventions. 


The Framework consists of:
- Core Elements: Activities directly handling product or material flows; and uniquely,
- Enabling Elements: those that remove obstacles for core actors.


Key elements of the circular economy

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Circle Economy's framework of strategies and activities that define the circular economy

Urban Opportunities

The Circular City Actions Framework provides urban changemakers with five complementary strategies they can use to start working towards a more circular system. 

The framework is action-based to provide users with concrete strategic directions and showcase the desired outcomes of each strategy. 
The framework consists of five complementary **strategies**, under which **sub-strategies** provide further detail. Finally, each sub-strategy consists of a diversity of tangible **solutions** which are framed in relation to key thematic areas. 

Note: solutions are currently focused on:
- 🍏 **Food systems**
- 🏢  **Built environment**
- 👕📱  **Consumer goods**
- ⚡ **Energy Systems**
- 🚌 **Mobility Systems**
- 💧 **Water Systems**

More thematic areas are coming soon...

'Click through each of the five strategy cards below to explore the framework and circular economy case studies in more depth!'



This framework was developed in collaboration with ICLEI, Metabolic and Ellen MacArthur Foundation with support from the MAVA Foundation. Read more about it [here]( https://circulars.iclei.org/action-framework/). 



Circular City Actions Framework

An action-based framework for local governments working towards circular cities

Thematic Areas

City Stakeholders

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Based on the work of [Bocken et al. (2016)](https://www.researchgate.net/publication/309699661_Product_design_and_business_model_strategies_for_a_circular_economy), the Four Flows Framework serves as a simple framework for managing resource flows in a circular economy by using less (Narrow), using for longer (Slow), using again (Cycle), and using clean, regenerative materials and energy (Regenerate).

These different principles of circular economy can be applied to our socioeconomic metabolism: we can design stocks like buildings, infrastructure, machinery, and vehicles to be rich resource mines for the future, and design manufactured goods and consumables to be cycled and made regenerative. Furthermore, the focus must also centre on getting more value out of fewer materials. Achieving the aims of a circular economy—minimising material use, regenerating the Earth, and preventing material losses—can be done through these four key strategies mentioned above.

Source: Circle Economy. (2023). *[The circularity gap report 2023](https://www.circularity-gap.world/2023)* (p.22). Amsterdam: Circle Economy. 

Four Flows Framework

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  Cities in China face significant water-related challenges, including flood, reduced water quality and severe water scarcity – exacerbated by rapid urbanization and more frequent extreme weather events.  Nearly half of cities in China do not meet national flood prevention standards and over half are considered water scarce.
To address these challenges, China is implementing the Sponge City concept which requires rethinking and redesigning urban and peri-urban environments in an ecologically-minded way. The aim of the Sponge City program is to ensure 80 percent of urban built-up areas in China meet Sponge City building requirements by 2030. This means that local governments rely on low-impact development principles and nature-based solutions to improve drainage, filter out pollutants and store up to 70 percent of excess rainwater for reuse during periods of drought. Local governments are key actors in redesigning the urban fabric and can take key actions such as strengthening collaboration between all stakeholders and adapting local policies and plans to enable Sponge City redevelopment.
You can read more about urban water challenges in China, the Sponge City concept and key actions local governments can take in this ICLEI briefing sheet.
Photo: (c) Shenzhen Urban Management Bureau 2017  

Chinese cities are struggling with flooding in urban, concrete areasSponge cities aim to capture and utilize this rainwater (CNN)Asian cities are struggling to accommodate rapid urban migration, and development is encroaching on flood-prone areas. Recent flooding in Mumbai was blamed in part on unregulated development of wetlands, while hastily built urban areas are being affected by flooding across India, Nepal, and Bangladesh. This is not a trend only in developing countries; floods in Houston, United States, highlighted the risks of development in environmentally sensitive and low-lying areas. In 2012, a severe flood in Beijing wreaked havoc on the city's transportation systems, and in 2016 floods overwhelmed drainage systems in Wuhan, Nanjing, and Tianjin. The challenges are clear.Groundwater over-extraction, waterway degradation, and urban flooding are forcing China's cities to address a vicious cycle. Sprawling urban development and use of impervious material prevent soil from absorbing rainwater, prompting further investment in infrastructures that typically impede natural processes and worsen flood impacts.China's "sponge city initiative" aims to arrest this cycle through the use of permeable surfaces and green infrastructures. However, the initiative faces two challenges: lack of expertise of local governments to effectively coordinate and integrate such a complex set of activities, and financial constraints.The conceptEngineering solutions are popular interventions, but cities cannot simply pipe away flood risks. To address the issue, China's sponge city initiative has an ambitious goal: by 2020, 80% of urban areas should absorb and re-use at least 70% of rainwater.Launched in 2015 in 16 cities, the initiative seeks to reduce the intensity of rainwater runoff by enhancing and distributing absorption capacities more evenly across targeted areas. The resulting groundwater replenishment increases availability of water for various uses. This approach not only reduces flooding but also enhances water supply security.The initiative is similar to the North American concept of low-impact development (LID), which according to the United States Environmental Protection Agency (EPA) mimics natural processes in order to protect water quality.The case of Lingang, a planned city in Shanghai's Pudong district, illustrates typical sponge city measures. These include rooftops covered by plants, scenic wetlands for rainwater storage, and permeable pavements that store excess runoff water and allow evaporation for temperature moderation.With ambitions to be China's largest sponge city project, the Lingang city government has invested $119 million in retrofits and innovations that could be a model for the majority of Chinese cities lacking modern water infrastructure.Chinese cities are making noteworthy efforts. In a pledge to expand coverage of urban greenery, Shanghai announced in early 2016 the construction of 400,000 square meters of rooftop gardens. The project is a collaborative effort among city regulators, property owners, and engineers. Sponge city projects in Xiamen and Wuhan have performed effectively during heavy rainfall.Improved policies and budgetsThe sponge city initiative requires a holistic and sustained effort, including effective environmental governance. However, concerns persist about weak regulations and selective enforcement. Local officials cannot simply turn the other way when violations are discovered. The unsung tedium of tightening controls is less exciting than bold innovations, but equally crucial for managing water. Gains from sponge city programs should not be offset by poor environmental governance.Funding is also a persistent constraint. To date, more than $12 billion has been spent on all sponge city projects. The central government funds roughly 15-20% of costs, with the remainder split between local governments and the private sector.Unfortunately, the initiative coincides with a burgeoning municipal debt crisis spurred in part by restrictive financial reforms, bond ratings cuts, and nervous bond markets. China's cities may soon find borrowing costs even higher and avenues for reducing debts narrower.Investment in sponge city initiatives is also proving to be an increasingly difficult sell, with only tepid interest from domestic private investors. The government should improve conditions that encourage investment, including tax incentives, better project transparency, and looser credit markets.Until this happens, sponge city initiatives will have to compete against visible and familiar infrastructure such as roads, transit, and utilities. They will also have to be attractive in a market with numerous other investment options.Innovative water initiatives have been adopted worldwide, including wetland restoration in the American Midwest, flushing systems using collected rooftop water in Oregon USA, bioswales in Singapore, and public spaces as flexible water retention facilities in the Netherlands.China has an opportunity to strengthen its emerging global leadership role in urban sustainability.However, it must first implement an effective vision for how sponge city initiatives complement broader environmental governance efforts. Improving regulatory enforcement and reviving interest in related private investment opportunities are two steps it can take.

China

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Government of China

Municipality of Lingang

<p>China's Sponge City program chose 16 pilot cities, later expanded to 30 cities, to design on low-impact development principles and nature-based solutions to improve drainage, filter out pollutants, and in a way that absorbs 70% of rainfall. The rainfall is collected in aquifers for later cleaning and re-use, minimising water waste. The program aims to ensure 80 percent of urban built-up areas in China meet Sponge City building requirements by 2030.</p>

China's Sponge Cities program

Business case

Direct and indirect reduction in economic costs

Cost Savings

Impact on the ease of innovation, and facilitating uptake of innovations

Innovation

Minimise waste through diversion: Instead of sending waste to landfill, it is redirected into other industrial processes for handling, treatment, recycling, recovery, or reuse in various forms. 

Minimise waste through design: At the outset of a process of project, plan and design such that there is zero waste or minimal waste during production, use, and at end of life. 

Minimise Waste (SDG12)

Account for the systems perspective during the design process, to use the right materials, to design for appropriate lifetime and to design for extended future use

Design for the future

Designing to reduce waste during production and use

Design out waste

Designing to enable multiple uses and lifecycles of a product and its materials

Design for cyclability

Engage with the government on circular policies and programmes

Government collaboration

Enacting measures that optimise water use

Water efficiency

Designing products so they use as little materials, water, energy, etc. as possible during use

Design for resource efficiency

Designing products that can easily breakdown and degrade in the environment

Design for bio-degradability

Participating in government programmes that support and advance the circular economy

Government programmes

A circular water economy reduces water consumption, reuses and recycles water and wastewater, and recovers materials, including heat and minerals, from water and wastewater to not only mitigate greenhouse gas emissions but also enhance resilience to climate change. A circular water economy preserves the health of water ecosystems using context specific approaches. 



WATER

 Spatial Planning

Slow strategies aim to keep materials in use for as long as possible, for example through design for durability and repairability. A more circular economy is also a slower one: materials, components, and products—and even buildings and infrastructure—that we lock in stocks are made to last. This will lower material demand in the long run, in essence also serving to narrow resource flows.

Slow

Cycle strategies aim to cycle and reuse materials at their highest value: they maximise the volume of secondary materials re-entering the economy, ultimately minimising the need for virgin material inputs and therefore also narrowing flows. Of course, virgin materials will always be needed to a degree: all materials degrade and can’t be cycled infinitely, use energy, and require blending with virgin materials to maintain strength and functionality.

Cycle


A small part of Shanghai is turning greener, street by street.
In the Lingang district, pavements are lined with trees, gardens and public squares full of plant beds. Between cranes and construction sites, plans display new buildings enveloped in the green and blue of parks, streams, and water features.
Lingang (also known as Nanhui after it was renamed in 2012) has a mission. As Shanghai’s “sponge city”, it is piloting an ecologically friendly alternative to traditional flood defences and drainage systems in the coastal city which faces long-term risks from rising sea levels.
Rapid concrete development in China has often blocked the natural flow of water with hard, impervious surfaces; to reverse this, the sponge city concept focuses on green infrastructure, such as wetland areas, rooftop plants and rain gardens.
“In the natural environment, most precipitation infiltrates the ground or is received by surface water, but this is disrupted when there are large-scale hard pavements,” says Wen Mei Dubbelaar, director of water management China at Arcadis. “Now, only about 20-30% of rainwater infiltrates the ground in urban areas, so it breaks the natural water circulation and causes waterlogging and surface water pollution.”

















  


 Permeable pavements in Lingang help stop buildup of surface water during heavy rain. Photograph: Helen Roxburgh


In Lingang, the wide streets are built with permeable pavements, allowing water to drain to the soil. Central reservations are used as rain gardens, filled with soil and plants. The large manmade Dishui Lake helps control the flow of water, and buildings feature green rooftops and water tanks.
 Since disastrous large-scale flooding in Beijing in 2012, flood prevention has rocketed up the state agenda. The Sponge City initiative was launched in 2015 with 16 “model sponge cities”, before being extended to 30, including Shanghai.
 “The first thing is to try and preserve or restore natural waterways, because that is the natural way to reduce the flooding risk,” says Prof Hui Li at Tongji University. “In Wuhan, for example, the main problem is that a lot of small rivers were filled in during building. That is a benefit the Lingang area has, as there is still a lot of agricultural land and a manmade lake which has capacity to hold more water during heavy rain. 

A satellite view of Lingang at the tip of the peninsula around 60 km south of Shanghai city centre. Credits Landsat 5 and landsat 8/Nasa

A satellite view of Lingang at the tip of the peninsula around 60 km south of Shanghai city centre. Credits: Landsat 5 and landsat 8/Nasa.


 “In the past, humans have taken the land away from the water; now we need to give the land back.”
 Lingang can introduce new innovations into its urban fabric, but retrofitting older areas in Shanghai is difficult. Recent redevelopments include the former industrial West Bund Riverside, using wetlands, permeable materials and raised walkways to make the area naturally “spongey”.
 But it is difficult to create room for new green space. Even existing parks are largely a missed opportunity, says Li, usually built higher than street level and failing to offer a natural escape route for runoff floodwater. Most focus is on green roofs – the Shanghai government wants 400,000 sq metres of new rooftop gardens – or gradually replacing pavements.
 By 2020, the government wants 20% of the built area of each pilot district to have sponge city functions, meaning at least 70% of stormwater runoff should be captured, reused, or absorbed by the ground. By 2030, a huge 80% of each city should meet this requirement. 
 This target puts pressure on new areas to compensate for older districts, where a wholescale retrofit by 2030 seems doubtful.
 There are plenty of other challenges. The central government will only provide about a fifth of funding needed – the rest must be raised by cash-strapped local governments and often unenthusiastic private investors. 
 Academics have warned planning models are not specific enough to accommodate the vast differences in China’s geography, and there is a sharp learning curve to match new concepts with city practicalities. In Lingang, for example, crossing the road is difficult due to the large rain gardens in central reservations.
 Nonetheless, urban planners say additional innovations have emerged from the process, including more sustainable design and relief for China’s water-starved regions by managing stored rainwater.

















  


 Wetland areas help to absorb rainwater in Lingang. Photograph: Helen Roxburgh


 “Sponge city infrastructure is beneficial because it is also changing the living environment, helping with pollution and creating a better quality of life in these areas,” says Dubbelaar. “The initial driver for sponge cities was the extreme flooding of urban areas, but the change in mindset, that development should have a more holistic, sustainable approach, is an extra benefit that is evolving during this project.”
 Lingang is clearly hoping its innovative greenery will bring tourists, with several hotel chains around the lake, a maritime museum and tourist information centre already open. One such visitor from the nearby suburbs says she is a fan of Lingang – she doesn’t know the term ‘sponge cities’, but she likes it.
 “I like all the trees and parks,” she considers. “It doesn’t really feel much like a city. I think it’s much more pleasant than other parts of Shanghai.”




Chinese cities are struggling with flooding in urban, concrete areasSponge cities aim to capture and utilize this rainwaterRecent flooding in Mumbai was blamed in part on unregulated development of wetlands, while hastily built urban areas are being affected by flooding across India, Nepal, and Bangladesh. This is not a trend only in developing countries; floods in Houston, United States, highlighted the risks of development in environmentally sensitive and low-lying areas. In 2012, a severe flood in Beijing wreaked havoc on the city's transportation systems, and in 2016 floods overwhelmed drainage systems in Wuhan, Nanjing, and Tianjin. The challenges are clear.Groundwater over-extraction, waterway degradation, and urban flooding are forcing China's cities to address a vicious cycle. Sprawling urban development and use of impervious material prevent soil from absorbing rainwater, prompting further investment in infrastructures that typically impede natural processes and worsen flood impacts.China's "sponge city initiative" aims to arrest this cycle through the use of permeable surfaces and green infrastructures. However, the initiative faces two challenges: lack of expertise of local governments to effectively coordinate and integrate such a complex set of activities, and financial constraints.Engineering solutions are popular interventions, but cities cannot simply pipe away flood risks. To address the issue, China's sponge city initiative has an ambitious goal: by 2020, 80% of urban areas should absorb and re-use at least 70% of rainwater.Launched in 2015 in 16 cities, the initiative seeks to reduce the intensity of rainwater runoff by enhancing and distributing absorption capacities more evenly across targeted areas. The resulting groundwater replenishment increases availability of water for various uses. This approach not only reduces flooding but also enhances water supply security.The initiative is similar to the North American concept of low-impact development (LID), which according to the United States Environmental Protection Agency (EPA) mimics natural processes in order to protect water quality.The case of Lingang, a planned city in Shanghai's Pudong district, illustrates typical sponge city measures. These include rooftops covered by plants, scenic wetlands for rainwater storage, and permeable pavements that store excess runoff water and allow evaporation for temperature moderation.With ambitions to be China's largest sponge city project, the Lingang city government has invested $119 million in retrofits and innovations that could be a model for the majority of Chinese cities lacking modern water infrastructure.Chinese cities are making noteworthy efforts. In a pledge to expand coverage of urban greenery, Shanghai announced in early 2016 the construction of 400,000 square meters of rooftop gardens. The project is a collaborative effort among city regulators, property owners, and engineers. Sponge city projects in Xiamen and Wuhan have performed effectively during heavy rainfall.The sponge city initiative requires a holistic and sustained effort, including effective environmental governance. However, concerns persist about weak regulations and selective enforcement. Local officials cannot simply turn the other way when violations are discovered. The unsung tedium of tightening controls is less exciting than bold innovations, but equally crucial for managing water. Gains from sponge city programs should not be offset by poor environmental governance.Funding is also a persistent constraint. To date, more than $12 billion has been spent on all sponge city projects. The central government funds roughly 15-20% of costs, with the remainder split between local governments and the private sector.Unfortunately, the initiative coincides with a burgeoning municipal debt crisis spurred in part by restrictive financial reforms, bond ratings cuts, and nervous bond markets. China's cities may soon find borrowing costs even higher and avenues for reducing debts narrower.Investment in sponge city initiatives is also proving to be an increasingly difficult sell, with only tepid interest from domestic private investors. The government should improve conditions that encourage investment, including tax incentives, better project transparency, and looser credit markets.Until this happens, sponge city initiatives will have to compete against visible and familiar infrastructure such as roads, transit, and utilities. They will also have to be attractive in a market with numerous other investment options.Innovative water initiatives have been adopted worldwide, including wetland restoration in the American Midwest, flushing systems using collected rooftop water in Oregon USA, bioswales in Singapore, and public spaces as flexible water retention facilities in the Netherlands.China has an opportunity to strengthen its emerging global leadership role in urban sustainability.However, it must first implement an effective vision for how sponge city initiatives complement broader environmental governance efforts. Improving regulatory enforcement and reviving interest in related private investment opportunities are two steps it can take.

The 34 hectares urban storm water park in the city of Harbin in northern China is an example of successful Sponge City intervention. The storm water park provides multiple ecosystems services: it collects, cleanses and stores storm water and lets it infiltrate it into the aquifers. At the same time it protects and recovers the native natural habitats and provides an aesthetically appealing public space for recreational use. Sponge City. Yet another term on the growing list next to regenerative, sustainable, green, eco, resilient, low-impact, future proofing, zero-carbon, and the list goes on.
Strange as it may sound, this term has actually gained a huge amount of support, especially in China. In fact, the Chinese government has already chosen 16 pilot cities and allocated to each of them between 400 and 600 million yuan for the implementation of innovative water management strategies that would gradually transform these cities into “Sponge Cities”.
What are the key issues the Sponge City wants to solve?
Before explaining in more detail what a Sponge City actually is, it is important to appreciate the main issues that the Sponge City intends to tackle. These are mainly four:

Less water available in urban and peri-urban areas. First of all, a key question we need to answer to explain this issue is: Where do we get the water that comes out of our taps? Many times it is actually coming from aquifers underneath our feet. As it rain, water is absorbed by the ground and naturally filtered by the soil. We can then extract this water by drilling wells into the ground and pumping water out of it. The water is then collected and treated before is distributed across the city and can reach every tap in each of our houses and offices. The problem is that extensive urbanization and urban sprawling led to the formation of thousands of square kilometres of impermeable areas made up of impervious roads, pavements, roofs and parking lots that do not allow water to be absorbed into the ground but that simply collect the rainwater through the urban drainage infrastructure and channel it into rivers, lakes or into the sea. This traditional type of design led to the creation of cities which are increasingly impermeable and have an increasingly greater impact on the natural water cycle. In practise this means that since less rain water is allowed to filter through the urban soil, less water is available to be extracted from aquifers in urban and peri-urban areas.
Polluted water discharged into rivers or the sea. Another key issues is related to the fact that rain water and wastewater (namely water from our sinks and toilets) is collected by one single drainage system. This drainage system (imagine one big pipe) collects all the rain water (when it rains) and the wastewater from our houses and directs it to a wastewater treatment plant where it gets treated before it is discharged again into rivers or the sea. When it rains, many times the wastewater treatment plant cannot accommodate all the water that the drainage systems carries. Therefore much of the rain water mixed with the wastewater is discharged untreated into rivers. The more impermeable the city is, the more water will be mixed with wastewater and will not be able to be treated but discharged directly into rivers.  This increases the level of pollution of local water bodies.
Degradation of urban ecosystems and green areas due to sprawling. This led to a considerable loss of urban biodiversity, a drop in available green areas for natural ground filtration of storm water, a decrease in CO2 capture by plants, fewer spaces for natural cooling through urban green microclimates and generally less liveable, healthy, comfortable and attractive public spaces.
Increase in the intensity and frequency of urban flooding particularly considering predicted increase in extreme weather events due to climate change. As the absorbing capacity of the urban surface is decreased, storm flooding risk is increased. Flooding leads to increased groundwater pollution and has considerable impact in terms of damage to properties and health related issues.

What is a Sponge City?
The Sponge City indicates a particular type of city that does not act like an impermeable system not allowing any water to filter through the ground, but, more like a sponge, actually absorbs the rain water, which is then naturally filtered by the soil and allowed to reach into the urban aquifers. This allows for the extraction of water from the ground through urban or peri-urban wells. This water can be easily treated and used for the city water supply.
What does a Sponge City need in practise? 
A sponge cities needs to be abundant with spaces that allow water to seep through them. Instead of only impermeable concrete and asphalt, the city needs more:

Contiguous open green spaces, interconnected waterways, channels and ponds across neighbourhoods that can naturally detain and filter water as well as foster urban ecosystems, boost bio-diversity and create cultural and recreational opportunities.
Green roofs that can retain rainwater and naturally filters it before it is recycled or released into the ground.
Porous design interventions across the city, including construction of bio-swales and bio-retention systems to detain run-off and allow for groundwater infiltration; porous roads and pavements that can safely accommodate car and pedestrian traffic while allowing water to be absorbed, permeate and recharge groundwater; drainage systems that allow trickling of water into the ground or that direct storm water run-off into green spaces for natural absorption
Water savings and recycling, including extending water recycling particularly of grey water at the building block level, incentivizing consumers to save water through increased tariffs for increase in consumption, raising awareness campaigns, and improved smart monitoring systems to identify leakages and inefficient use of water.

What are the benefits of a Sponge City? 
There is wide range of benefits associated with the implementation of sponge cities. These include:

More clean water for the city. Replenished groundwater and thus greater accessibility to water resources for cities. This also entails greater water self-sufficiency which allows cities to increasingly rely on water sources from within their boundaries
Cleaner groundwater due to the increase volume of naturally filtered storm water. This means lower environmental and health costs due to considerable decrease in water pollution
Reduction in flood risk as the city offers more permeable spaces for the natural retention and percolation of water. This leads to better resilience and in particular greater ability to deal with higher flood risks resulting from climate change
Lower burdens on drainage systems, water treatment plant, artificial channels and natural streams. This also entails lower costs for drainage and treatment infrastructure
Greener, healthier, more enjoyable urban spaces. Greener urban spaces improve quality of life, create more pleasant landscape aesthetics and recreational areas that are enjoyable and attract people. This also means increase in land value due to aesthetically more pleasing, cleaner and healthier open spaces close to private properties
Enriched biodiversity around green open spaces, wetlands, urban gardens and green rooftops



Harbin

Chongqing

Wuhan

Amoy

Shanghai

<p>Contrary to conventional flooding infrastructure trying to keep water away, a new concept of 'sponge cities' aims to design cities so that they can soak up and store rainwater for later use. Cities struggling with flooding or water scarcity (or both) can address those issues by working together with nature rather than pushing the water away. Most of the involved cities have not only improved flood protection, but also their quality of life.</p>