Chinese cities manage flooding with traditional drainage systems that lead water into rivers or the sea. Due to relatively low requirements for the amount of water those systems have to handle, increasing urbanisation, construction activity, and increased rainfall, flooding risk in Chinese cities has increased significantly.

Between 2008-2010, 137 cities were flooded more than 3 times a year, and 57 cities were flooded for more than 12 hours. At the same time, rainwater that gets discharged into rivers or the sea leaves the city and does not replenish the groundwater supply, leading to scarcity of water in the city - a problem that affects 30 out of 32 Chinese megacities.

The sponge cities program chose 16 pilot cities, later expanded to 30 cities. Contrary to conventional flooding infrastructure trying to keep water away, a new concept of “sponge cities” aims to design cities so that they can soak up and store rainwater for later use. This means that local governments rely on low-impact development principles and nature-based solutions to improve drainage, filter out pollutants and store up to 70 percent of excess rainwater for reuse during periods of drought. 

This happens through low-intervention and low-cost infrastructure like permeating pavements that allow water to penetrate the ground and replenish groundwater supply, or rooftop gardens which absorb rainfall.

At the same time, areas like Lingang in Shanghai used more extensive measures like creating artificial wetlands, which retain and purify stormwater naturally. Drainage systems are led into underwater storage tanks and tunnels rather than the rivers in order to retain stormwater and combat water shortages.

The aim of the Sponge City program is to ensure 80 percent of urban built-up areas in China meet Sponge City building requirements by 2030.

Photo by Darmau Lee on Unsplash