China's 'sponge cities' aim to re-use 70% of rainwater

(CNN)Asian cities are struggling to accommodate rapid urban migration, and development is encroaching on flood-prone areas. 

Recent flooding in Mumbai was blamed in part on unregulated development of wetlands, while hastily built urban areas are being affected by flooding across India, Nepal, and Bangladesh. 

This is not a trend only in developing countries; floods in Houston, United States, highlighted the risks of development in environmentally sensitive and low-lying areas. In 2012, a severe flood in Beijing wreaked havoc on the city's transportation systems, and in 2016 floods overwhelmed drainage systems in Wuhan, Nanjing, and Tianjin. 

    The challenges are clear.

    Read: A third of Bangladesh under water as flood devastation widens

    Groundwater over-extraction, waterway degradation, and urban flooding are forcing China's cities to address a vicious cycle. Sprawling urban development and use of impervious material prevent soil from absorbing rainwater, prompting further investment in infrastructures that typically impede natural processes and worsen flood impacts.

    China's "sponge city initiative" aims to arrest this cycle through the use of permeable surfaces and green infrastructures. 

    However, the initiative faces two challenges: lack of expertise of local governments to effectively coordinate and integrate such a complex set of activities, and financial constraints.

    Parts of China are especially prone to floods. In summer 2016, torrential rains caused damage across northern China.

    Launched in 2015 in 16 cities, the initiative seeks to reduce the intensity of rainwater runoff by enhancing and distributing absorption capacities more evenly across targeted areas. The resulting groundwater replenishment increases availability of water for various uses. This approach not only reduces flooding but also enhances water supply security.

    The initiative is similar to the North American concept of low-impact development (LID), which according to the United States Environmental Protection Agency (EPA) mimics natural processes in order to protect water quality.

    The case of Lingang, a planned city in Shanghai's Pudong district, illustrates typical sponge city measures. These include rooftops covered by plants, scenic wetlands for rainwater storage, and permeable pavements that store excess runoff water and allow evaporation for temperature moderation.

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    Chris Alexakiswater