The Sponge City initiative, first conceptualized by the Chinese government in the early 2010s following disastrous large-scale flooding in Beijing, aims to break the cycle of urban flooding by turning impervious surfaces into "sponges" through the use of permeable surfaces and green infrastructure, including wetlands, green rooftops and rain gardens (Construction21, 2019). The Sponge City initiative was officially launched in 2015, with 16 model sponge cities located around China, before being extended to 30, including Shanghai in 2016. Per the national government directive, by 2030, 80% of each identified city should have sponge city functions; namely, at least 70% of stormwater runoff should be captured, reused or absorbed by the ground (Roxburgh, 2017). Responsibility for implementing the Sponge City initiative lies with the individual sub-provincial or municipal level government entities (Xu, 2020). Approximately 15-20% of funding is provided by the national government, and the remaining costs are split between local governments and the private sector (Griffiths et al., 2020).

Shortly after being identified as a sponge city, the Shanghai government issued regulations on the initiative's planning and construction which outlined that all urban planning should consider ecosystem services (Ke, 2021). Drawing on the natural process through which precipitation infiltrates into the groundwater table or is received by surface water resources, sponge city infrastructure is beneficial for ecosystems: it helps with pollution control and creates a better quality of life, exemplifying a more holistic and sustainable approach to urban planning (Roxburgh, 2017).

Shanghai's first sponge city pilot area was in the Pudong, home to the city's largest sponge park "Starry Sky", which measures 54ha (38ha of land and 16ha of water area) (Ke, 2021). The park has the typical designs of sponge city infrastructure, including permeable pavement and rain gardens, but it also includes a landscape ecological corridor, a wetland, urban rainwater storage and water purifying facilities (in this case, a 30cm thick rubble layer under the soil to filter water) (Ke, 2021). Across Shanghai's 16 districts, there are numerous examples of sponge city designs: wide streets to allow for permeable pavements that leads to underground water purification and storage infrastructure, central reservations used as rain gardens, conservation green spaces, and buildings with green rooftops and water tanks (Roxburgh, 2017; Griffiths et al., 2020; Ke, 2021). A current priority for the Shanghai government is to gradually replace all paved surfaces with more porous materials, though the more recent focus has been on ensuring all new builds have green rooftops and retrofitting older buildings (Roxburgh, 2017).