In particular, the over-extraction of groundwater, the degradation of water bodies and wetlands, and urban flooding are forcing Chinese cities to address a complex puzzle: The surface development in cities leaves little opportunity for natural systems to mitigate rainwater runoff and replenish groundwater.
But the initiative faces three challenges: already polluted groundwater, a focus on spot-level solutions, and the constrained fiscal capacity of local governments. The sponge city initiative, a joint effort of three ministries－housing and rural-urban development, finance, and water resources－has ambitious goals: by 2020, 80 percent of urban areas should absorb and reuse at least 70 percent of rainwater.
First mentioned by President Xi Jinping in 2013 and officially launched in 2015 in 16 cities, the initiative approaches urban water sustainability from two angles: it reduces the intensity of rainwater runoff and distributes absorption more evenly; and the resulting groundwater replenishment increases the supply of reusable water feeding into existing systems (channeled runoff is often treated then discharged, removing it from usage circulation).
The pilot case of Lingang, a new town project on the coast near Pudong, Shanghai, illustrates typical sponge city measures: rooftops covered with plants, scenic pools and wetlands for rainwater storage, and permeable pavement that stores runoff water and allows evaporation for temperature moderation.
Many projects are spot-level solutions at particular sites.
To date, more than $12 billion has been spent on sponge city projects. The central government funds 15 percent to 20 percent of the costs, with the remainder split between local governments and the private sector.
The government has acknowledged this growing challenge and now provides resources and guidance, while enterprising localities compete to fund innovative proposals with ambitious targets.
To complement sponge city investment, the central government should now take additional measures to improve groundwater quality, adopt a whole-of-system approach for pollution control and incentivize private investment.