These terms, devices, and practices have been grouped together in the literature under the umbrella of green infrastructure — as opposed to gray infrastructure consisting of concrete, cement, and asphalt. More recently, they have come to be known as nature-based solutions (NbS). The sponge city concept, developed in China, gained momentum in the 2010s. Such cities mimic elements of nature or incorporate nature into urban infrastructure, as explained by a group of foreign authors in a paper published in the Urban Water Journal, in 2015.
A common factor among these technologies is that they challenge the urban drainage paradigm that has prevailed throughout the twentieth century, namely, quickly moving water away from developable land. “As a nature-based solution, sponge cities challenge the historical way in which urban planning has related to water,” says urban planner Raquel Rolnik, of the University of São Paulo’s School of Architecture and Urbanism (FAU-USP).
“Since the end of the nineteenth century, and especially in the twentieth century, city planning has been anti-water. There is an attempt to remove its presence from cities. As such, cities invest in river channelization systems, flood embankments, canal filling, and underground drainage. The strategy aims at gaining as much land as possible for development by waterproofing urban areas,” states the researcher, who is the provost at the USP campus in Butantan, in São Paulo City.
The Chinese approach, which is taking shape in the 30 pilot cities, gained notoriety after its implementation. “The sponge city example demonstrates that it is possible to adopt a sustainable urban drainage design,” argues landscape architect and urban planner Paulo Pellegrino, of FAU-USP, a scholar of the best practices for flood and urban rainwater control and author of several articles on the subject.
“The projects developed by Kongjian Yu, a sponge city pioneer, and other Chinese experts have shown that it is possible to implement these interventions, dispelling criticism that there was no space for them,” says Pellegrino. “Where there were channelized rivers, Yu worked to rebuild the banks with marshes, floodplains, wetlands, and transition areas. In addition to reducing the speed of runoff, he created space for water to spread out.”
The originators of the sponge city concept combined the millennia-old traditional knowledge of farmers who have worked with water, using techniques such as terracing (building terraces on mountain slopes to prevent erosion), in conjunction with new Western technology to develop their projects.
In an interview with Pesquisa FAPESP, Yu highlighted that even a metropolis like São Paulo could be transformed into a sponge city, but with one caveat. “We need to solve the problem of flooding on two scales: on an urban level and on a regional level. Urban and regional sponge systems are needed to manage the river basins,” says the expert, who founded Beijing University’s School of Architecture and Landscape Planning and who is president of the Turenscape office.
“If public officials are determined to fix the problem, a strong and organized government could transform the city into a water-resilient sponge city in five years,” argues Yu.
Kongjian Yu / TurenscapeFenghuang: 12-kilometer highway in the Chinese province of Hainan was given nature-based solutions developed by YuKongjian Yu / Turenscape
With or without the sponge city label, the use of nature-based solutions to address rainwater drainage has proliferated worldwide. Copenhagen in Denmark, Malmö in Sweden, the city-state of Singapore, Portland in the United States, and Amsterdam in the Netherlands, have already adopted such elements to deal with water.
Most scientific articles that use the term sponge city are written by Chinese researchers, as indicated by a systematic literature review published two years ago by a group from the University of Pernambuco in the journal Research Society and Development. Among the 25 articles analyzed, 19 had been written in China. Resilience to flooding was the most significant contribution found in the cities studied, the article identified.
However, the model’s challenges and limitations are also discussed. A review article published in Water Science & Technology, in 2023, shows that 19 of the 30 pilot cities in China reported flooding after implementing the solutions. “Sponge cities, LID, and other alternative rainwater management systems cannot be treated like a one-size-fits-all model, since they depend on the physiological characteristics of the [water] reservoir in question, the regional climate, and the hydraulic and hydrological parameters,” emphasize the authors.
The researchers mention that it is easier to implement the model in newer cities, as opposed to those that have been established for longer, because they have less vacant land. Even the public-private partnership encouraged in China during construction of the sponge cities is questioned, since involvement of the private sector remains insignificant, according to the study.
Many challenges arose after the work was completed, as a result of mistakes made during construction, such as use of the incorrect type of vegetation or maintenance difficulties. “The sponge cities are not a magic solution that eliminates flooding or handles all intense rainfall, but they can divert water during peak flow and reduce its intensity,” state the article’s authors.
Léo Ramos Chaves / Revista Pequisa FAPESPGreen roof on a building along Avenida Paulista and a rain garden in the neighborhood of Pinheiros, both in São PauloLéo Ramos Chaves / Revista Pequisa FAPESP
Flash floods and retention basins
A sponge city, explains Pellegrino, of FAU, is based on the principle that a water basin has three distinct functions along its length. The first takes place at the boundary of the basin, at the headwaters, where the water begins to flow. “At this point, we must adopt strategies to retain water at the source, by building rain gardens, rain ponds, and permeable pavement,” he says.
Then, there are the slopes surrounding the basin, where the water flows down to the bottom of the valley. “In these intermediary regions, we need to reduce the runoff speed. We can use bioswales, rain garden beds, and lots of vegetation.”
Finally, we need to create space to accommodate the water that reaches the lowest point, where the floodplains originally were. “Porto Alegre and Vale do Taquari are located precisely there. We need to consider structures and spaces to receive this water. This is nothing new. We seem to be suffering from collective amnesia,” says Pellegrino, referring to the current predominance of gray infrastructure in the cities.
The paradigm shift around water drainage, according to experts, has been taking place for 30 or 40 years, with the realization that the model used in decades past will not solve the issue of heavy rainfall. The first hegemonic response, they say, was the creation of retention basins, large urban reservoirs, sometimes covered, intended to retain stormwater. But these structures, common in São Paulo, have functional and urban limitations, they say.
“One of the most dangerous processes related to rainwater on hillsides is flash flooding, where water rushes downhill at fast speeds. The retention basins do not solve this because they are located at the bottom of the valley,” notes architect and urban planner Luciana Travassos, of the Federal University of ABC (UFABC). “They are seen as urban fractures with complex links to other city infrastructure,” says the researcher.
Travassos coordinates the Territories of Water project, which proposes developing a program to conserve and restore permanent preservation areas (PPA) in the municipality of São Paulo. Supported by FAPESP’s Public Policy Research Program, the work is being carried out in partnership with the Department of Greenery and the Environment of the Municipality of São Paulo (SVMA) and the National Observatory for the Rights to Water and Sanitation (Ondas).
Most of São Paulo’s PPAs cover a 30-meter protected strip along the banks of each river and waterway, says the expert. The project proposed by her group, which began in February, includes the use of NbS in the areas along the city’s rivers and streams. It also includes a study of the policies adopted for permanent preservation areas over the last two decades. Researchers want to assess how municipal public policies have addressed rivers and their banks, as well as their characteristics, whether there are precarious dwellings, allotments, and other infrastructure occupying the PPA, which affect the possibility for intervention. “From there, we will establish prioritization and management criteria, based on environmental justice, and define a basin to work with,” says Travassos.
Brazilian experts have developed projects in line with the initiatives adopted by the sponge cities. “Nontraditional solutions, such as rain gardens, green roofs, and residential water storage tanks, are becoming more common,” notes civil and sanitary engineer Marcelo Obraczka, who teaches a course in sanitary engineering and the environment at Rio de Janeiro State University (UERJ) and who coauthored an article about rain gardens published last year in Mix Sustentável. “However, we can’t completely abandon conventional urban drainage solutions.”
Also at UERJ, architect Luciana Mattos dos Anjos Galdino, of the Engineering and Infrastructure Division at the Brazilian National Cancer Institute (INCA), used her master’s thesis, which she defended in 2022, as a case study for applying the sponge city concept in Cruz Vermelha Square, in Rio de Janeiro.
“I have spent 13 years working at INCA, located downtown, between Lapa and Central do Brasil. In addition to being a major thoroughfare, it has a lot of foot traffic. With the smallest amount of rain, the area floods and turns into chaos,” she says. In her study, she proposes building water squares in two areas, in order to contain surplus rainwater, and utilizing permeable pavement, rain gardens, and green roofs.
Rivaldo Gomes/FolhapressRetention basin in Vila Prudente, in the capital of São Paulo, during constructionRivaldo Gomes/Folhapress
The problem in São Paulo
Architect and urban planner Adriana Sandre, founder of the Guajava architecture firm in São Paulo and lecturer at FAU-USP, recognizes that it is not easy to build large sponge installations like those built by the Chinese in densely populated areas that resemble the Anhangabaú and Pirajussara watersheds in the capital of São Paulo. “We would need to expropriate large areas, and in São Paulo, that would be difficult,” says the researcher, who participated in preparing nearly 20 watershed plans for the municipality of São Paulo, with projects envisioned by the city council.
She explains that the plans — instruments aimed at reducing flooding within the city — included some decentralized NbS and water reservoirs, avoiding the use of concrete retention basins. As an example, she cites the case planned for Anhangabaú Valley, where they designed infiltration wells — an element that, in many cities, is mandatory for approval of the building plans — rain roofs, and bioswales on Avenida 9 de Julho, which runs alongside it.
One of the researcher’s current projects is studying how to address the effects of climate change in areas peripheral to the cities. “What type of project can be implemented in the favelas, many of which are located on valley floors? How do we transpose the idea of sponge cities, which entail large areas of development, onto areas of high building density?,” asks Sandre, who acted as a consultant for the Periferia Viva – Favela Urbanization program, due to be launched soon by the federal government.
According to Pellegrino, of USP, although a challenging task, it is possible to make São Paulo more of a sponge city, even though the Tietê and Pinheiros river floodplains are urbanized. “There are many options, a multiplicity of elements at various scales that can be used in the city. It is up to the municipal government, the developers, and the population to assess what these solutions are and where they can be slotted in,” she states. “The idea is to not allow the water to flow too quickly or concentrate in low areas. Even in the old river floodplains, there are spaces the can be used for retention, such as garden beds, squares, parks, and parking lots.”
Although specific projects in São Paulo have adopted nature-based solutions and strategies to reduce the speed of water flow, construction is moving in the opposite direction and gray infrastructure prevails. “Driving water downhill only increases the size of the snowball. This vision still prevails,” comments Pellegrino. Rolnik, of FAU-USP, agrees. “São Paulo’s master plan, approved last year, does not prioritize nature-based solutions. The real estate-financial complex defines the type of real estate products that will be developed in the city and the political-contractor complex defines the nature of the public works and interventions,” she states.
Experts stress the importance of reversing this scenario, since the capital of São Paulo is located in the headwaters of the Tietê river basin, with a complex hydrological network made up of more than 1,500 kilometers of small streams, some of which are channelized and covered. Even so, they argue, there are opportunities for intervention, particularly considering the need to urbanize the favelas, many of which occupy the banks of rivers and streams.
The sponge city concept is quite important in several aspects for containing flooding in the Metropolitan Region of São Paulo, particularly in the capital and the ABC region,” says Travassos, of UFABC, the lead author of an article about the topic published in Frontiers in Sustainable Cities, in 2022. “We must work with the idea of a sponge city that is a hybrid of green and gray solutions, ranging from small reservoirs in buildings to linear parks, in permanent preservation areas, in rivers and streams. To do this, we must coordinate with social housing projects.”
Project
Water territories: Conservation and Recovery Program for Permanent Preservation Areas in the Municipality of São Paulo (nº 23/10072-0); Grant Mechanism Public Policy Research; Principal Investigator Luciana Rodrigues Fagnoni Costa Travassos (UFABC); Investment R$693,704.91.
Scientific articles
MOURA, N. C. B & PELLEGRINO, P. R. M. et al. Best management practices as an alternative for flood and urban storm water control in a changing climate. Journal of Flood Risk Management. june 17, 2015.
LI, HUI et al. Sponge City Construction in China: A survey of the challenges and opportunities. Water. aug. 28, 2017.
FLETCHER, T. et al. Suds, LID, BMPs, WSUD and more – The evolution and application of terminology surrounding urban drainage. Urban Water Journal. vol. 12, no. 7, pp. 525–42. july 2014.
MENEZES, L. et al. Cidades-esponja e suas técnicas compensatórias: Uma revisão sistemática de literatura. Research Society and Development. july 2022.
CHIKHI, F. et al. Review of sponge city implementation in China: Performance and policy. Water Science & Technology. vol. 88, no. 10, pp. 2499–520. nov. 2023.
GONDIM, F. et al. Jardins de chuva: Atualizações sobre a técnica a partir de uma revisão sistemática. Mix Sustentável. vol. 9, no. 5, pp. 201–15. oct. 2023.
TRAVASSOS, L. & MOMM, S. Urban river interventions in São Paulo municipality (Brazil): The challenge of ensuring justice in sociotechnical transitions. Frontiers in Sustainable Cities. jan. 14, 2022.
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