Nature's Solution: How 'Sponge' Cities are Revolutionizing Urban Flood Management

In the face of rising intense storms and urban flooding, one Chinese landscape architect is challenging the norm by embracing nature instead of controlling it. Kongjian Yu, founder of Turenscape, has been designing 'sponge cities' for over a decade, allowing nature to soak up and retain stormwater before releasing it back into the environment. These projects, which vary in form and scale, create new parks, restore wetlands, and install rain gardens and permeable pavements, among other features. Yu argues that traditional concrete- or pipe-based solutions are expensive, inflexible, and require constant maintenance. Instead, he proposes creating areas with porous earth where local plants can thrive with little maintenance. This approach allows the earth and plants to soak up water, preventing or reducing flooding in nearby areas. Excess water is slowed down by vegetation, unlike concrete which can speed up water flow and exacerbate flooding. Turenscape has planned and designed over 10,000 of these projects in more than 250 cities worldwide, completing over 1,000 of them. China, where more than 70 cities have implemented sponge city initiatives since 2015, is particularly vulnerable to flooding, with 641 of its largest cities facing regular flooding. This vulnerability has been highlighted by recent flash floods and deadly landslides following torrential rain.

While sponge cities have been successful in alleviating or reducing the impact of medium or large amounts of rainfall, they struggle to cope with extreme rain. Experts suggest that sponge infrastructure must be supplemented with 'hard engineering' like dams and embankments to tackle the heaviest rains. Yu acknowledges that sponge cities can still overflow if projects aren't properly designed or built, or if rainfall is too extreme. However, he argues that flooding occurs in places that 'are not spongy enough', and that more sponge projects are needed to make cities more resilient. Beyond flood mitigation, sponge cities offer other environmental benefits, such as reducing urban temperatures, addressing water shortages, and providing pleasant environments for residents. In Wuhan, for example, local air quality, biodiversity, and lower temperatures have been recorded since the construction of more than 380 sponge projects. Yu's pioneering work has been recognized by The Cultural Landscape Foundation, which awarded him the $100,000 Oberlander Prize in 2021. His large-scale projects and ability to affect change set him apart apart from his contemporaries.

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