Chongqing - "Sponge City" is no stranger to Chinese citizens, but most of them assume that it is just another fancy term imported from overseas. Even though there is no denying that "Sponge City" is part of a worldwide movement by various names, such as green infrastructure in Europe, low-impact development in the United States, and nature-based solutions in Canada, the very concept of "Sponge City" is an urban development model for flood management proposed by Chinese researchers in early 2000.

The Sponge City Initiative

Over the past 40 years, China has urbanized on an unprecedented scale, with the country's urbanization rate increasing from 17.55% in 1977 to 60.60% in 2019. Rapid urbanization comes hand-in-hand with the country's extraordinary economic boom, but cities are built at the expense of green spaces, therefore posing significant challenges for flood management.

Conventionally, modern cities are often equipped with "grey infrastructure" such as concrete pavement, urban drainage systems, and dykes & dams for water management. While insufficient grey infrastructure can lead to flooding and pollution, excessive development of this infrastructure might cause water shortages and the overall degradation of the ecosystem. Chinese researchers' proposal of sponge city presents a much-needed alternative to solve these problems.

Influenced by the concept of low-impact development in the west, which features minimizing the effects of urbanization on nature, Chinese researchers went a step further on coexisting with nature. They came up with the bold idea of turning cities into giant sponges to embrace rainfall: with the construction of green roofs, urban wetlands, and corner ponds, cities can be built to absorb water in the rainy seasons and release water during the dry days.

Becoming a Nationwide Policy

Due to the persistent advocacy by Chinese researchers, in a speech at the Central Government Work Conference on Urbanization in December 2013, Chinese President Xi Jinping endorsed "Sponge City" for the first time. "When upgrading the urban drainage system, priority should be given to retaining rainwater and using the power of nature to drain it. We should build sponge cities with natural drainage, retention, penetration, and purification systems for water," Xi said.

Subsequently, the State Council issued the Guideline on Promoting the Construction of Sponge City, which set the goal that sponge cities will collect and utilize 70 percent of the rainwater, with 20 percent of urban areas meeting the target by 2020 and 80 percent by 2030.

In 2015 and 2016, two batches of state-level pilot cities, including Beijing, Shanghai, Shenzhen, and Chongqing, were organized to carry out the Sponge City Initiative, with the central government's financial support of up to 0.5 billion yuan. In 2017, "Sponge City" was even officially stated in the Chinese government work report, becoming a hot topic at all levels of government throughout that year.

The Controversy over the Zhengzhou Rainstorm

The construction of sponge cities occurs through upgraded urban planning and construction, giving full play to the impact of converted buildings, permeable pavements, and green spaces. According to the 2018 White Paper on Sponge City Construction in China, after three years into the sponge city initiative, the number of sponge cities in China has reached more than 370.

Take Chongqing as an example, following the strategy of "one national pilot area + three municipal pilot districts", the sponge city area of Chongqing has reached 421 square kilometers by 2020, which is about 24.2% of the urban area, successfully realizing the national target of more than 20%. Currently, the city is working on the goals of the city's 14th Five-year Plan, which proposes that by 2025 more than 45% of the urban area will meet the requirements of sponge city.

But bitter controversies were stirred up after a once-in-a-hundred-year rainstorm hit Zhengzhou. Within four days from 18th July 2021, nearly a year's volume of rain fell on Zhengzhou, one of the 30 pilot cities that has spent about 50 billion yuan on the sponge city construction. The catastrophic flooding killed more than 300 people, left 50 people missing, and caused worldwide media debate on the efficacy of sponge city. Some foreign media even mocked that this flood had shattered the myth of China's sponge city.

So, is sponge city the answer for flooding or not? The answer is divided depending on the scale of the flood. Some people tend to neglect that, in China, the sponge city is only part of a broader plan to curb flooding and improve the urban environment. It’s never meant to deal with climatic extremes and uncertainty. "Sponge cities are only viable for mild or small rainstorms, but with the extreme weather in Zhengzhou, we still have to combine it with traditional infrastructures such as drains and pipes," multiple experts from home and abroad voiced similar views in the post-flood interviews.

The Embodiment of Chinese Philosophy

Yu Kongjian, dean of the College of Architecture and Landscape at Peking University and the researcher who was credited as one of the creators of "Sponge City", defended in an interview with ASLA that "Since ancient times, Chinese cities along the Yellow River have used ponds to manage flooding and stormwater, So we know these approaches worked for over 2,000 years because these cities survived."

Drawing wisdom from ancient philosophies like Taoism, the Sponge City concept in fact embodies harmony and reconciliation with nature, which was put into practice in flood management in China thousands of years ago. The notion is not just a fundamental rethink of flood control. Rather, it's a revolutionary integration of ancient Chinese wisdom with modern urban planning and management.

China carries on the Sponge City approach despite the controversy over Zhengzhou. By the end of April 2022, China has announced the second round of selection for sponge city demonstration cities. While citizens of pilot cities are already reaping the benefits, other cities are scrambling to catch up. Through the sponge city initiative, ancient Chinese wisdom is carried forward into a new era and will continue to shine in modern days.