Absorb, Adapt, Thrive: Exploring the Potential of Sponge Cities for Climate Resilience
by Elaina Geiger
Elaina Geiger is a first-year Master of City Planning student studying Land Use and Environmental Planning. After graduating from the University of Pittsburgh as an environmental engineering student in April of 2023, Elaina has continued to explore her passion for the natural environment and how it can best coincide with
the environment that we build. In her free time, you can find her walking around Philly, with a coffee in hand and headphones blasting Taylor Swift, in search of her favorite street in the city.
Cities around the world are faced with adapting to a changing global climate. Whether it’s extreme heat or high levels of precipitation, urban spaces are evolving to sustain these new, more extreme environmental challenges. At the same time, cities are growing in size and population, with a predicted 5 billion people living in cities by 2030 [1]. Cities may account for this influx of residences by physically expanding their infrastructure, oftentimes using materials such as asphalt and concrete to do so. These materials are considered to be impervious, and in the event of high rainfall, these surfaces can cause high quantities of stormwater runoff that could lead to overloaded systems and flash flooding.
For example, San Diego, a drought-prone city in California that averages about 10 inches of rain a year, experienced four inches of rain in one week in February 2024, [2] resulting in overloaded stormwater systems that led to to severe and dangerous flooding [3]. Materials like concrete and asphalt are also known to absorb as much as 95% of the sun’s energy, which is then radiated into the surrounding environment, making cities hotter [4]. In order to combat climate change and create resilient cities, an alternative to these impervious materials must be found.
Sponge Cities and their Design
[1] TheWorldCounts.com. "World Urban Population." Last modified February 23, 2024.
[2] Carol, John. "The atmospheric river has passed over LA and San Diego, with another storm behind it," February 6, 2024.
[3] Rivas, Alexis and Dorfman, Mike. “San Diego city leaders said stormwater system
was vulnerable months before rainstorm,” NBC San Diego, January 29, 2024.
[4] Zafra, Mariano. “The floor is lava: How concrete, asphalt and urban heat islands add
to the misery of heat waves,” Reuters, July 31, 2023.
A “sponge city” is an urban planning model recently created in China that uses green infrastructure to manage flooding and urban heat in cities vulnerable to environmental threats. These cities contain an abundance of natural green spaces such as forests, lakes, and parks that are intended to absorb rain and prevent flooding [5]. They can also use tools and technology such as green roofs, green facades, and swales to create more absorbent surfaces in place of the typical impermeable materials used for these structures. This concept has been popular in cities around the world struggling with environmental challenges that are exacerbated by climate change. On a smaller scale, Toronto, Canada, has an eco-roof incentive, encouraging homes and buildings to opt for green roofs to help mitigate stormwater management [6].
There has been an abundance of media coverage surrounding cities taking concepts from sponge city projects to gradually implement into their urban environment as this issue becomes more pressing for some regions around the world. The term “sponge city” is meant to reflect the city’s ability to capture water, much like a reservoir, and absorb it rather than repel it.
Because these cities are holding water within the natural and sustainably-built environment instead of losing it to evaporation, they are also more resilient to drought and dry spells.
Another benefit to sponge cities is that structures and implemented design solutions can clean rainwater in the absorption process. Using permeable roads to collect rainfall not only prevents the collection of littered or larger materials from being swept up into the stormwater runoff, but can also filter out smaller particles in the process of seeping into the ground or
green spaces. For example, Lingang Park in Shanghai uses sponge city infrastructure to both retain rainwater from runoff and purify the water through eco-engineering. The park is divided into four quadrants that consist of wetlands, ponds, and floating islands. The sponge park is placed between two rivers where water is pumped from one river through the sponge park, into the other. Water is pumped into the park through a skimmer that removes surface debris from the runoff, which then travels through filtration ponds containing aquatic plants that help to purify the water. According to an engineer with the China Construction Technology Consulting firm, the system can purify “up to 15,000 cubic meters of water per day, as the water quality rises from Grade V to Grade III when it flows back to the river" [7]. For context, water quality that ranks Grades I to III are suitable for all applications, whereas Grade V water is unsafe
to use for any purpose [8].
[8] Yu, Jiawen et al. “A Comparative Study of Water Quality and Human Health Risk
Assessment in Longevity Area and Adjacent Non-Longevity Area,” National Library
of Medicine, October 4, 2019.
[9] Climate Risk and Resilience in China (CRR). “Xiamen: Adapting to Climate Change
with Sponge City Construction,” Climate Cooperation China, July 7, 2020.
[10] OW US EPA, “Nonpoint Source: Urban Areas,” Overviews and Factsheets, Sep-
tember 15, 2015.
[11] Yi, Xing. “Sponge City”
[12] Climate Risk and Resilience in China.
Sponge cities are developed using design methods that have minimal negative impacts on the environment, including Low Impact Development (LID) and Water Sensitive Urban Design (WSUD) [9]. These initiatives refer to systems that use natural processes when managing stormwater in order to protect water quality and the associated ecosystem [10]. Each of these initiatives include a set of principles that can be applied to urban design methods to create climate-resilient cities such as sponge cities. With flooding being one of the most serious water-related issues that China faces in today’s climate, the country has launched a pilot program using a combination of these principles to broadly implement sponge city principles. The aim is to have 80 percent of urban areas embedded with “sponge facilities to absorb and reuse at least 70 percent of rainwater" [11]. There are currently 30 metropolises that are participating in the campaign to make Chinese cities “spongier.”
An example of a sponge city’s design implementation is in Xiamen, China. In 2015, the city was selected as an early-stage pilot for environmentally sustainable flood control methods to be applied to a city susceptible to water-related issues. Studies have shown that the city experiences varying precipitation patterns, with a decrease in the number of annual precipitation days, yet an increase in the average precipitation intensity. According to China’s Climate Risk and Resilience (CRR) plan, Xiamen’s sponge city initiatives prioritize environmental aspects such as runoff and water quality, rainwater utilization rates, and wastewater recycling rates. The plan has established the goal of “building a comprehensive and holistic water system that helps prevent and cope with water-related disasters”. The city has also outlined a set of objectives to guarantee an “improved water environment” split into six different systems, including pollution prevention and control, river and lake water network construction, garden and green space construction, drainage and waterlogging prevention, road traffic construction, and sponge community construction [12].
To highlight a particular goal, the sponge community construction objective highlights two recommendations to achieve an effective and successful sponge city: the
reconstruction of the old community, and the construction of the new community. Through the reconstruction of the old community, it was important to planners to improve upon the infrastructure in a way that does not entirely strip its heritage, but instead improves the efficiency and sustainability of existing structures. This includes increasing the permeable pavement rate in reconstruction to no less than 40% of surfaces in the sponge city without digging up roads with a cultural or historical significance. The construction of the new community requires that all new roads and squares in all residential areas are to be paved with permeable pavement, with the rate for new construction not less than 70 percent. Permeable concrete is an important aspect of sponge cities, as it allows for water from precipitation to pass directly through, therefore reducing the stormwater runoff that may occur in the event of a major rainfall. Permeable pavements also prevent pollutants from travelling into stormwater systems, absorbing them upon contact, rather
than having them swept up with stormwater runoff into sewage systems.
Image: A view of Nandong New District from Dengtashan Park.
Source: Ajew
Case Study: Xiamen, China
Image: Rooftops in Shanghai.
Source: kafka4prex/Flickr
[5] Harrisberg, Kim. “What are ‘sponge cities’ and how can they prevent floods?” Unit-
ed Nations Framework Convention on Climate Change, April 11, 2022
[6] City of Toronto, “Green Roofs,” City of Toronto
[7] Yi, Xing. “Sponge city,” China Daily, Last updated October 29, 2021
[8] Yu, Jiawen et al. “A Comparative Study of Water Quality and Human Health Risk
Assessment in Longevity Area and Adjacent Non-Longevity Area,” National Library
of Medicine, October 4, 2019.
In planning these projects, there
must be equitable access to services
and opportunities, participation in
decision-making processes, and the
acknowledgement of vulnerable groups
In 2015, regions of Xiamen that were prone to flooding and other water-related issues were chosen as the pilot projects of sponge city construction, including the Yangtang residential area. This 620,000 m 2 area previously consisted of villages, bare soil, farmland, and ponds, but due to a housing demand in the city, the area was converted into a residential community. In the face of development, the area experienced many urban water-related issues such as surface runoff pollution and road water accumulation. In order to combat these issues, the construction objectives included source reduction and intermediate transfer of stormwater runoff, as well as a complex underground pipe network to control the flow of water under and around the community. Facilities such as sunken green spaces, biological retention zones, and green roofs were also included in the development of this pilot sponge city project.
Despite the environmental benefits that sponge cities can provide for urban areas faced with extreme effects of climate change, there are also some challenges that must be considered before a wide implementation of this concept. In planning these projects, there must be equitable access to services and opportunities, participation in decision-making processes, and the acknowledgement of vulnerable groups [13]. An impact assessment conducted for Baicheng City, another sponge city pilot project in China, shows that although the sponge city program has enhanced distributional equity, there is a need to
achieve procedural justice for disproportionately affected communities when it comes to the decision-making process. The issue of underrepresented communities being left out of the planning process is broader than just sponge cities, and conceptual planning must incorporate justice into policy and design.
Also, there are some central contradictions surrounding the environmental and economic agendas of a sponge city, and whether or not the effort is an excuse for new investment in the urban construction and financial innovation fields. This development may offer local government more opportunities
for private investors to profit off of infrastructure projects for sponge cities. It might also justify the “direct intervention of the government in financing and construction through a local expansion agenda” [14]. Although this may not necessarily be true for all cities implementing a sponge city design, it is worth considering to ensure that the development is in good faith, as well as transparent and honest. It is difficult to find any clear results of how the implementation of sponge city systems have improved or changed the built environment of Xiamen, or any city for that matter. There is yet to be an update of the success of these concepts nearly 10 years after first mention of sponge cities in a city’s climate action plan, and few other cities have followed in Xiamen’s footsteps. There are aspects of sponge cities that many cities have adapted, such as green roofs and rain gardens, but not many places have taken on the challenge in developing a large-scale region into a sponge city by definition. This could be
due to a lack of sufficient proof or information on the environmental benefits that sponge cities provide.
Overall, a main challenge that cities around the world face with the escalation of the climate crisis is how to be responsive to shocks like changing weather, extreme conditions, and other climate hazards. New designs and concepts like sponge cities can help to solve the issue of cities being unprepared for future conditions. These concepts, while their implementation outcomes are uncertain, may have an important place in building climate-resilient cities across the globe.
Continuing Challenges and Opportunities
