Following devastating flooding in New Zealand this week the idea of developing 'sponge cities' has re-emerged, but what are they?

In most urban cities the outlook is grey. Concrete, tarmac, and brickwork all contribute to elevated flood risks, create urban heat islands, and harm nature. Which is why China are approaching things differently.

Wetlands, grassy areas, and vegetation soak up water whereas most urban materials result in rainwater sitting on the surface, contributing to floods.

Sponge city elements aim to mimic the natural world’s ability to soak up this water through the use on permeable surfaces on roads and pavements, allowing enough room and time for water to drain rather than collecting and causing rapid flooding.

Tests in a small number of cities including Beijing and Shenzhen were successful and resulted in the Chinese Government committing to transform 80% of urban spaces in the country into sponge cities by 2030.

Not only will this help prevent flood damage, save lives, and aid ecosystems with new habitat space, it also helps prevent catastrophic failures which other measures can create.

Large dams used to control reservoirs and rivers can hold back a colossal amount of water during heavy downpours but when they fail can result in areas downstream being devastated.

Kongjian Yu of Peking University pioneered research into sponge cities and claims that if just 1% of land is used solely for water drainage almost all major flooding events in urban areas could be prevented.

With the creation of new green spaces and natural habitats these cities also aid in the fight against climate change. A factor which is slowly worsening flood events around the world.