Sponge city (Chinese: 海绵城市) is an urban planning idea created in China by Kongjian Yu. It focuses on using natural systems, such as parks, wetlands, and permeable paving, to manage water and reduce flooding. Instead of relying only on drainage systems, sponge cities use green spaces to absorb rainwater, which helps prevent floods, reduces water shortages, and lessens the heat island effect. These areas also support wildlife and improve water quality. In 2014, the Chinese Communist Party (CCP) and the State Council approved sponge city as a national policy for urban development.

Sponge city design uses natural landscapes to collect, store, and clean water. This idea is inspired by traditional methods used in southeastern China to manage water during heavy rains. Chinese officials explain that sponge cities are similar to other global approaches, such as "green infrastructure" in Europe or "low-impact development" (LID) in the United States. However, sponge cities differ from LID by combining natural and technical methods, while LID mainly uses technical solutions. Sponge city design helps improve water quality, create habitats for wildlife, and connect water systems across cities and regions. This model protects and restores ecosystems, allowing nature and humans to coexist. Unlike industrial methods that use levees, channels, and pavement to quickly move water away, sponge cities mimic natural processes by letting water stay in wetlands and floodplains.

Background of issue

Urbanization leads to the building of grey infrastructure, such as roads and buildings, in cities. Too much use of grey infrastructure can cause water shortages, pollution, and harm to natural water systems. Current city planning often creates many buildings, which reduces green spaces and limits the ability of cities to collect rainwater and drain water properly. This makes it difficult for rainfall to meet the water needs of modern cities, leading to problems with water ecosystems and aquatic environments.

High-intensity construction, like buildings, roads, and public squares, makes the ground too hard, changing the natural surface and how water moves through the ground. Because of this, surface water flow increases from 10% to 60%, while water soaking into the ground drops greatly, sometimes to zero. A 2010 study by the Ministry of Housing and Urban-Rural Development found that 62% of 351 cities in the country faced flooding between 2008 and 2010. Of these, 137 cities flooded more than three times during this time. This frequent flooding has made people realize the importance of protecting water ecosystems and building better urban ecological systems. The old idea of quickly moving water away, a traditional grey water management method, is no longer effective for solving rainwater problems during rapid city growth. To address these issues, China is focusing more on managing urban flooding and improving water ecosystems, promoting the concept of Sponge City.

History of Sponge City

The People's Republic of China started the Sponge City initiative because traditional flood control and stormwater systems failed to manage water effectively. This idea was first shared by urban planners and environmental experts in China through letters and proposals sent to government leaders beginning in the early 2000s. Although the concept was introduced and tested before 2000, the severe flood in Beijing on July 21, 2012, which caused 79 deaths, led top government officials to adopt the Sponge City plan as a national policy.

In 2015, China began testing the Sponge City approach in 16 districts. Over the following years, more cities were added to the program. By 2017, four groups of cities had been selected, totaling 87 cities. The timeline for the Sponge City pilot projects was:

• 2015–2018: Use small-scale projects to test Sponge City designs in urban areas.
• 2018–2020: Develop standards, management rules, and monitoring systems to recycle 70% of rainfall.
• 2020–2030: Fully integrate Sponge City principles into urban planning nationwide.

China’s goal is for 80% of its cities to collect and reuse 70% of rainwater. Creating Sponge Cities does not always require large amounts of money. However, many people misunderstand this because of misleading media reports and the misuse of the term by some local governments, contractors, and unqualified designers. These groups often use "Sponge City" as a slogan without following the actual nature-based solutions it represents. Major challenges include the continued use of traditional infrastructure, decorative landscaping, and outdated urban planning rules. Securing funding for Sponge Cities has also been difficult.

After success in China, the Sponge City model was adopted by cities in regions facing extreme weather conditions, such as Dhaka and Kenya, as well as major cities like Berlin and Los Angeles.

On September 23, 2025, Kongjian Yu, the creator of the Sponge City model, died in a plane crash near Aquidauana, Mato Grosso do Sul, Brazil.

Design principles

The Sponge City idea is to spread and hold water where it starts, slow its movement, clean it naturally, and adjust to water when it gathers. This is very different from traditional methods, which use large reservoirs to collect water, fast-moving pipes and drains to speed water away, and tall flood walls and dams to stop water at the end. The Sponge City theory focuses on natural methods, managing water at its source, adapting to local conditions, protecting nature, learning from natural systems, keeping as much natural space as possible in cities, restoring plant and animal life, and creating pleasant landscapes. These goals can be achieved through natural water absorption, natural water seepage into the ground, and natural water cleaning. These ideas come from long-used practices in China, where water was managed carefully around the environment instead of using large infrastructure. Natural features like hills and land shapes help water seep into the ground, plants and wetlands clean water, and a mix of natural and human-made systems allow cities to take in and release rainwater. Green spaces and water areas in cities—such as wetlands, rain gardens, green rooftops, sunken parks, grassy ditches, and ecological parks—are the main parts of the Sponge City system.

Creating these systems has three main parts: protecting natural areas in cities, restoring damaged ecosystems, and using low-impact development.

• Protection means keeping natural areas like rivers, lakes, and ditches safe. Natural plants, soil, and tiny living things are used to slowly improve water quality and fix damaged ecosystems.
• Restoration includes finding natural areas, building paths to connect them, creating networks, and marking areas for water and green spaces to restore water ecosystems.
• Rules apply to roads, green spaces, water systems, homes, and buildings to protect natural areas, keep their ability to hold water, manage water at its source, and create sponges of different sizes.

These design ideas can be used at three levels:

• Large scale: planning for whole regions or watersheds
• Medium scale: planning for cities, towns, or villages
• Small scale: individual parts like parks or neighborhoods

Sponge City plans are often used in new buildings more than in older ones built during recent fast city growth. Examples include Xiamen’s Yangfang neighborhood and Shanghai’s Langang Park, which are new developments. Shougang Park, once a steel factory, was turned into a park that includes the 2022 Winter Olympics Big Air venue and uses Sponge City ideas.

Political applications

In December 2013, at a meeting about urbanization, Xi Jinping, the leader of China, said that improving city drainage systems should focus on keeping some rainwater and using natural methods to remove water. He described building "sponge cities" that can hold, absorb, and clean rainwater naturally. To support this, the Ministry of Housing and Urban-Rural Development released technical guidelines in October 2014. These guidelines highlighted the need for careful planning of rainwater management and emphasized using nature as a key principle in city development.

In August 2015, a new method was introduced to evaluate how well sponge city projects work. This method outlined how to use government funds and set standards for pilot cities to show progress. Based on these rules, a design system was created to guide the construction of new buildings, roads, parks, and water systems that help manage rainwater.

A government guideline from 2015 (Guobanfa [2015] No. 75) explained that sponge cities are built by improving city planning and using buildings, roads, green spaces, and water systems to manage rainwater. By 2020, 20% of urban areas were expected to collect and use 70% of rainwater, and by 2030, this goal would expand to cover 80% of urban areas.

In 2015 and 2016, the government selected 16 cities, including Zhenjiang, Jiaxing, and Xiamen, as the first group of pilot cities for sponge city projects. A second group of 14 cities, such as Shenzhen, Shanghai, Tianjin, and Beijing, was also chosen to continue the work. The government encouraged partnerships between public and private groups to provide more financial support.

However, some challenges remain. These projects are expected to cost about $230 billion by 2030, but the national government plans to cover only one-fifth of the costs. Some pilot cities, like Ningbo, have experienced flooding since the program began, which may make private investors hesitant.

China’s central government requires that by 2030, 80% of urban areas must include sponge city features, and at least 70% of rainfall must be collected and reused.

Pilot projects

In 2015, sixteen cities in China were selected for the first group of pilot projects. The cities are listed below:

• Baicheng
• Qian'an
• Jinan
• Hebi
• Xixian New Area
• Zhenjiang
• Jiaxing
• Chizhou
• Wuhan
• Changde
• Chongqing
• Suining
• Gui'an New Area
• Nanning
• Pingxiang
• Xiamen

In 2016, fifteen cities were selected for the second group of pilot projects. The cities are listed below:

• Beijing
• Tianjin
• Dalian
• Qingyang
• Guyuan
• Xining
• Shanghai
• Ningbo
• Fuzhou
• Shenzhen
• Zhuhai
• Yuxi
• Sanya

Effectiveness and monitoring of sponge cities

Sponge cities have been shown to achieve the following:

• Recharge groundwater
• Adapt to disasters or changes
• Help restore the environment
• Use fewer city water pipes
• Improve city ecosystems
• Clean water using plants
• Prevent sewer backups
• Reduce stormwater runoff
• Help prevent flooding
• Support natural systems

• Connect cities to share information

Studies show that sponge cities are very effective at reducing stormwater runoff and improving water quality. Their effectiveness has been tested through models or by observing results, since detailed monitoring data is not widely available. It has been hard to collect monitoring data because the government has not set clear standards for monitoring or evaluation.

Right now, flood control effects are usually limited to small areas instead of the whole city because projects are small-scale. Out of 30 pilot cities, 19 have had flooding since the program started. However, areas in cities that were redesigned with sponge city ideas have had little or no flooding during big storms.

Key examples of sponge city implementation

Benjakitti Forest Park is located in downtown Bangkok, Thailand. The land was once a brownfield because it was the site of a tobacco factory. The area faced problems like sinking ground and flooding due to city growth. In 2023, Turenscape developed the 52.7 square hectometers of land into a public green space. The park includes 187,500 cubic meters of storage for stormwater, which is enough to handle a 10-year rainfall event. This design helped protect the park and nearby areas from flooding during a major rain event in 2022, while much of Bangkok flooded. The park also includes features like sponge wetlands, a boardwalk for recreation, a flood-safe amphitheater, buildings for sports and museums, and spaces for plants and animals. The project was created with a low cost ($20 USD per square meter) and requires little maintenance.

The Luotian River, which is about 8 kilometers long, uses natural methods to manage stormwater as part of the Luotian Water Comprehensive Regulation Project. The river channel was widened to restore areas near the river and expand existing reservoirs into storage lakes for rainfall. Rainwater is used as a water supply instead of being sent directly into the river. Data shows that this design improved water quality and reduced flooding. Success required cooperation between cities along the river to maintain the natural connection of the river.

Gui-an New District, one of the pilot cities, was established in 2014. $1 billion USD was invested in sponge city design, which includes paving that allows water to pass through and 70 monitoring stations. However, as of 2022, many parts of the design, including the monitoring stations, were not completed. Pervious concrete was installed but often not maintained. Modeling showed that the design reduced flooding risk but did not completely eliminate it. The success of flood control depends on the strength of the rainfall event.

Sanya City is a pilot city in the second group of projects. Located on an island, the city faced flooding and damage to natural habitats. To address these issues, a mangrove park and a wetland park were created to reduce flooding and restore the environment.

A 10-hectare area along the Linchun River was restored into a mangrove to improve flood resilience. Urban development led to concrete flood walls being built, which harmed the mangrove habitat. The area was turned into a mangrove park by restoring the land next to the river. A special land design called "interlocking finger" (ecotones) was used to reduce the force of ocean tides and storm surges, protecting the mangroves. Terraces were built from the city streets to the river, with bio-swales to collect and clean runoff. Three years after construction, the mangrove has grown healthily, and the area has seen improvements in water quality and biodiversity.

In downtown Sanya, a 68-hectare park was once polluted by illegal waste and overgrown with invasive plants. Pond-and-dike systems were built to collect and clean stormwater. A forested wetland was created in the center of the park, with recreational areas around it. The wetland can store 830,000 cubic meters of stormwater, reducing flood risk. Nearby communities have seen less flooding and polluted runoff. The park has also attracted wildlife and provided new spaces for recreation.