Sponge Cities—The Future of Flood Management?

As a result of heavier rain caused by climate warming that increases the moisture evaporating into the atmosphere, we have witnessed a rise in flood rates in recent years. In light of this, the need for an effective plan to manage floods and natural catastrophes is increasingly urgent. To this end, the concept of the sponge city was conceived by Kongjian Yu, head of the college of architecture and landscape at Peking University, China.

Prof. Dr. Kongjian Yu is the Guest Editor of MDPI Special Issue Challenges in City Design: Realize the Value of Cities in Challenges, which investigates solutions to the problems faced as a result of increased urbanization and promotes ecological urbanism.

The sponge city is a flood management framework, which aims to control flooding, limit water scarcity, and reduce water pollution. While most current systems implemented in cities to combat or reduce flooding include concrete-reinforced riverbanks, drains and pipes to keep water out, sponge cities, in brief, form a sort of permeable sponge, in which a large number of natural pools collect the excess water, which is then absorbed and gradually transported via soil and wetlands to large bodies of water, e.g., rivers and lakes. Other elements include rooftop gardens in cities with a large number of high-rise buildings, which help to capture and absorb rainfall and reduce the likelihood of flooding, and permeable pavements and roads.

This process has many advantages. Among them, the filtration of the water through vegetation purifies it and removes contaminants before its extraction from the ground via wells, facilitating its treatment and reuse. Additionally, as water is transported to aquifers more effectively, surface runoff is reduced. Furthermore, sponge cities create the added benefit of more green open spaces, increasing the quality of life of residents and wildlife.

Experts have posited that we have become increasingly disconnected from nature over the years, and Kongjian Yu’s proposal is based on working with nature instead of against it—embracing floods rather than fearing them. He strongly believes in the superiority of this concept compared to modern infrastructures and hopes that many other countries will follow suit in future years.

China is no stranger to flooding; thus, in an attempt to take measures against these events, after its initial proposal in 2014 by Chinese researchers, the sponge city project commenced in China in 2015, when 16 Chinese cities were chosen to pilot the new construction. Another 14 were added in 2015. These include Wuhan, Xiamen, and Beijing. By 2030, the 30 participating cities must have incorporated ‘sponge’ elements into 80% of their urban areas—which will help to reduce the heat island effect in big cities—and will also have to recycle a minimum of 70% of their rainfall.

However, some researchers have criticised the model, arguing that it is not suitable for extreme, large-scale flooding and that in denser areas, there may be insufficient space to implement sponge city features. Further investigation, therefore, may need to be conducted into the feasibility of sponge cities in different parts of the world.

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Examples of MDPI papers discussing areas of China in which plant life is being used to help reduce the risk of flooding include the following: Sponge City Program (SCP) and Urban Flood Management (UFM)—The Case of Guiyang, SW China in Water; Hydrological Effects of Urban Green Space on Stormwater Runoff Reduction in Luohe, China in Sustainability; Effectiveness Analysis of Systematic Combined Sewer Overflow Control Schemes in the Sponge City Pilot Area of Beijing in IJERPH; SuDS & Sponge Cities: A Comparative Analysis of the Implementation of Pluvial Flood Management in the UK and China in Sustainability.