Floods hit Hue city, Vietnam, in 2020. Via Wikimedia Commons By Lê Minh Đức CC BY-SA 4.0

This article was submitted as part of the Global Voices Climate Justice fellowship, which pairs journalists from Sinophone and Global Majority countries to investigate the effects of Chinese development projects abroad. Find more stories here.

In March 2025, torrential rains inundated the streets of Jakarta, the capital of Indonesia. The heavy rainfall caused severe deluge in the city and its nearby areas, killing at least nine people and displacing 90,000. It also reminded residents of painful memories from 2020, when intense flooding in the metropolitan city killed at least 60 people. 

Social media was soon flooded with videos of the disaster, the ensuing evacuation missions, and first responders’ mitigation efforts. One such video shows emergency personnel rescuing people in boats and trying to clear flooded roads by shooting the excess water into the river with firetrucks.

@tawabb_

Inalillahi, turut berduka atas musibah Hari ini, Selasa 4 Maret 2025 Banjir di sejumlah Wilayah Jabodetabek .. 📍Kali Ciliwung, Jatinegara, Jakarta Timur

♬ suara asli – Tawabb – tawabb_

Inalillahi, turut berduka atas musibah Hari ini, Selasa 4 Maret 2025 Banjir di sejumlah Wilayah Jabodetabek .. 📍Kali Ciliwung, Jatinegara, Jakarta Timur

To Allah we belong and to Him we return, condolences for the disaster today, Tuesday, March 4, 2025 Floods in a number of areas of Jabodetabek .. 📍Ciliwung River, Jatinegara, East Jakarta

Other major cities in Southeast Asia have also been devastated by severe floods caused by extreme weather. 

Parts of metropolitan Manila, the capital of the Philippines, experienced flooding from phenomenal rainfall at unprecedented intensity this August. According to expert analysis, the downpour in the city was equivalent to about five days of rain, dumped in just one hour. In Ho Chi Minh City, Vietnam, after heavy thunderstorms this September, streets were submerged by over a meter of water, triggering widespread traffic gridlock. Residents had to abandon their vehicles and wade through flooded roads during rush hour.

Extreme weather events linked to climate change are occurring at a higher frequency and intensity in Southeast Asia. This exacerbates urban flooding, a chronic problem in many sprawling megacities in the region due to outdated urban planning, low-lying coastal positions, and oversaturated land. 

Heavy rain caused flash floods in Quezon City, the Philippines, in 2023. via Wikimedia Commons. CC-BY-SA-4.0 

Urban flooding is also common in China, as 641 of the country's 654 largest cities are affected by regular flooding, especially megacities on its eastern and southern coast.

In order to resolve the problem of urban flooding, China incorporated the concept of “sponge cities” (海绵城市) into its national policy in 2013, and pilot projects featuring this concept have subsequently launched in scores of cities across the country.

What is a sponge city?

One of China's most prominent urban architects, Yu Kongjian (俞孔坚), proposed the sponge city method for managing floods. 

Yu uses a sponge as a metaphor for cities’ rainwater storage capacity. While conventional flood water management focuses on draining water away as quickly as possible through engineered drainage infrastructure, such as pipes and water channels, sponge cities emphasize the opposite — absorbing water and slowly releasing it, like a sponge. 

“Floods are not enemies,” Yu explains. “We can make friends with floods. We can make friends with water.”

Tianjin Qiaoyuan Park in Tianjin, China, is one of the early sponge city projects. Image via Wikimedia Commons by Mydogistiaotiaohu CC BY-SA 4.0

As cities expand, natural ground is replaced by impermeable surfaces, such as concrete and asphalt, that prevent water from being absorbed. Yu believes that the destruction of many natural water systems, such as rivers, lakes, and wetlands, due to rapid urbanization, is one of the key reasons why flooding disasters occur so frequently in Chinese megacities today. The sponge city model focuses on restoring natural water systems, enabling the land to absorb rainwater, thereby mitigating flooding disasters and reusing the rainwater locally. In an interview with the Chinese state-funded People's Daily, Yu explained his belief that overreliance on “grey” infrastructure (such as concrete dams and pipelines) can be limiting:

工业化大家相信人类的技术、人类的机械工程、钢筋水泥工程能够征服自然。因为它有科学的模型，它能计算出水流，能计算出运动的轨迹，能计算出河道。越直、越硬、越光，它的过水越快，它的防洪效果越好。就是这种工程机械的，这种机械的工程思维，就是单一目标的思考。

Industrialization has fostered a belief that human technology, mechanical engineering, and reinforced concrete can conquer nature. Because it has scientific models, it can calculate water flow, calculate movement trajectories, calculate river channels. The straighter, harder, and smoother, the faster the water passes, the better the flood control effect. This is the kind of engineering machinery, this kind of mechanical engineering thinking, that is, single-minded thinking.

In 2013, Chinese President Xi Jinping announced his support for sponge cities and made them a top priority for the future.

解决城市缺水问题，必须顺应自然。比如，在提升城市排水系统时要优先考虑把有限的雨水留下来，优先考虑更多利用自然力量排水，建设自然积存、自然渗透、自然净化的'海绵城市'。

To solve the problem of urban water shortages, we must adapt to nature. For example, when improving urban drainage systems, we should prioritize keeping limited rainwater, prioritize using more natural forces for drainage, and build ‘sponge cities’ with natural accumulation, natural infiltration, and natural purification.

Some of the strategies employed to create these so-called sponge cities include green roofs, rainwater storage and infiltration systems, sunken green spaces, permeable pavement, bioretention ponds, wetland revitalization, restoring natural waterflow pathways, and more.

Researchers have found that the sponge city projects in China have significantly improved stormwater runoff control and helped reform unfavorable geographical environments. 

Adaptation in Southeast Asia

Yu believes that his water management concept will be effective in flood-vulnerable countries such as Bangladesh, Malaysia and Indonesia, while some other countries including Singapore, the US and Russia are already benefiting from the implementation of similar concepts. 

In an interview with the Chinese media Sanlian Lifeweek, Yu points out that China and Southeast Asia share the same challenges brought by monsoon climates. 

在季风性气候下，降雨严重不均，一天可能有200毫米的雨降下来，再大的地下蓄水空间，再粗的排水管道和强大的排水泵站，都没办法解决瞬时的排洪排涝问题……最有效的解决方法就是基于自然、适应于自然、借助于自然来解决问题。

Under a monsoon climate, rainfall is extremely uneven. In a single day, as much as 200 millimeters of rain may fall, and no matter how large the underground water storage space, how wide the drainage pipes, or how powerful the pumping stations, the problem of discharging floodwaters instantaneously cannot be solved….the most effective solution is to address problems by being based on nature, adapted to nature, and making use of nature.

Conventional water management approaches, which mainly focus on channeling rainwater out of the city, are unsuitable for cities with monsoon climates, Yu states. 

“These cities fail because they have been colonised by Western culture and copied their infrastructure and urban model,” he says in an interview with the BBC.

Yu and his team have applied the sponge city concept in the bustling urban heart of Bangkok, where they transformed the site of a former tobacco factory into Benjakitti Forest Park. The park reduces the destructive force of stormwater, filters contaminated water and provides a wildlife habitat as well as a public recreational space to residents, according to a press release by Turenspace, an urban design company founded by Yu.  

The project demonstrated success in the summer of 2022, when Bangkok experienced a 10-year rainfall event. Much of the city was flooded, while the park and its vicinity were not.

The design goals of Tianjin Qiaoyuan Park include containing and purifying urban stormwater and improving the saline-alkali soil through natural processes. Image via Wikimedia Commons by Joshua L. CC BY 2.0

Controversies and challenges 

At the same time, sponge cities have faced controversies and skepticism. Though the concept has been piloted in many Chinese cities, it is mostly implemented on a small scale in individual neighborhoods, streets, or areas. As a result, its flood mitigation impacts are often limited to the local level, rather than city- or nationwide. 

In a previous interview, Yu himself acknowledged that scaling up the pilot projects in Chinese cities is challenging, as it demands cross-departmental collaboration, requiring strong political will and extensive administrative coordination.

Some critics also point out that the sponge city design often can’t fully cope with the unprecedented levels of rainfall brought on by the climate crisis. In 2021, when heavy rainfall hit Henan province in China, floods killed 292 people in its capital city, Zhengzhou, which is a major pioneer of the sponge city concept. Many questioned the effectiveness of the sponge city infrastructure after the fatal disaster. 

The floods in 2021 caused great damage to the city of Zhengzhou. Image via Wikimedia Commons  CC BY-SA 4.0

Worse still, under climate change, extreme weather events are becoming more frequent and severe. Some critics argue that design standards are not always fully updated to withstand intensifying precipitation trends under climate change.

Hu Gang, a Chinese urban planning expert explains that the sponge city model can only function during moderate or light rainfall, but not during a recording-breaking rainstorm. To alleviate urban flooding caused by extreme rainfall, Hu says that in addition to continuously building sponge city infracture, establishing a more comprehensive drainage system, emergency shelter and disaster preparedness plans are also key solutions.

From the perspective of Southeast Asia, there are obstacles to implementing the sponge city concept. For example, for flood-prone Jakarta, the high cost of developing sponge city infrastructure is often cited as one of the biggest challenges. Other obstacles include an aging drainage system and a lack of space for new construction or redevelopment in the overcrowded capital.

In 2022, Indonesian officials announced that to absorb rainfall and minimize flood damage, the sponge city concept would be implemented in Indonesia's upcoming capital city, Nusantara, which is currently being constructed in East Kalimantan and will replace Jakarta upon completion. The city is being built from the ground up, and officials are claiming it will be the “world's most sustainable city.” The project is one of the first instances of a country moving its capital due to climate pressures, and has not unfolded without controversy. 

Nusantara will incorporate large open spaces connected to its hydrological system to retain and store rainwater, according to the report. The new capital city will also feature porous road surfaces and green rooftops to reduce direct runoff. However, the construction of the new capital city is currently shadowed by budget cuts, and concerns grow that the development of Nusantara will not be completed anytime soon.