Tackling the challenges of sponge cities

From the staggering population migration to the multi-lane traffic jams, China's rapid urbanization has captured global attention. But much of what threatens the sustainability of China's urbanization is not above ground but under it.

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. The result is a vicious circle of investment in rainwater infrastructure and new land development that exacerbates the runoff problem.

China's sponge city initiative aims to arrest this cycle through permeable surfaces and "green infrastructure". 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.