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All the newsThe sponge city, an efficient answer to water shortage in southern China?
At the end of 2021, the megacities of southern China warned their inhabitants and took measures to limit water consumption as the Donjiang river (East), the tributary of the Pearl River, has been affected for several years by severe drought. It is the main source of water supply for the cities of Guangzhou and Shenzhen, but between January and October, the volume of rainfall decreased by a quarter in comparison to the average of the previous decade, according to the municipality of Guangzhou.
Is the principle of sponge cities, already applied in several Asian cities, the answer to this water shortage? Two researchers specialised in water are working on this issue. They have published their thoughts in the review, The Diplomat.
The demand for water is rising constantly
90% of the water of the city of Shenzhen, with a population of 40 million, comes from the East River, which serves other large urban centres like Hong Kong and Guangzhou.
Demographic growth, coupled with economic activities, is placing too much pressure on increasingly scarce water resources. Forecasts estimate that there will be a lack of 890 million cubic meters by 2030.
The local government has declared several emergency measures such as the re-use of wastewater and the detection of leaks in the distribution networks. Other actions for the long-term may be taken, such as transfers of water between basins and nature-based solutions, clearly apparent in the concept of sponge cities where water can better infiltrate and where rainwater can be held and stored, making it possible to manage water in the city more sustainably.
Rethinking urban planning
Sponge cities seek to reduce the impact of floods and water shortages by integrating water as a resource and not as a threat to the city. This new model of urban development is influenced by the Chinese concept of harmonious development between human beings and nature, low impact development, and by experiments performed elsewhere to drain rainwater.
Based on a systemic approach to the water cycle in the urban environment, the sponge city avoids as much as possible the elimination of rainwater in drains and rivers in order to promote a circular economy of re-using. Recourse to non-conventional water sources to satisfy domestic and industrial uses is also encouraged, such as the desalination of seawater and the treatment of grey water.
In 2020, the re-use of water in Shenzhen amounted to 125.5 million cubic meters (mostly recycled used water), i.e., about 6% of the total water supply. Shenzhen aims to reach a rate of used water recycling of 15% of its total water supply, versus 27% in Pekin and 40% in Singapore. A pilot city chosen in 2016 by the Chinese authorities to implement the national sponge city programme, Shenzhen has already converted more than 28% of built areas according to these new criteria and aims at reaching 80% by 2035.
However, the concept has already shown several limits regarding adaptation to climate change, by not taking enough account of the risk of drought. Initially developed to prevent floods, the sponge city must also satisfy the growing demand for water and the acceleration of the frequency and intensity of extreme meteorological phenomena.
To cope with water shortages in Shenzhen, the objectives of sponge cities will have to be redirected from the reduction of flood risks and the pollution of runoff water to the reduction of demand for freshwater and greater re-use of rainwater and used water.
Lastly, green solutions should not be limited to urban areas, since water is by nature a “thread of life” that joins territories together. This transformation must be achieved at the larger scale of river basins to implement a global policy of integrated water resource management in the Greater Bay area.
To learn more about the climatic disturbances in Southeast Asia, read the article IAGF: Exceptional floods in Southeast Asia