Are 'sponge cities' enough to curb climate-fueled floods?

With its coastal forests, sugarcane farms and sweeping beaches, South Africa’s Durban might appear to be an ideal “spongy” city — one capable of absorbing water, which can be useful in combatting both flood disasters and drought.

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One year after the city’s devastating floods, green experts are highlighting the importance of using what cities already have — such as parks and rivers — to reduce risks, and figuring out what else they need to be as resilient as possible as climate change threats intensify.

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But sponginess is just a starting point, they say, noting that policies, funding and infrastructure to protect communities are equally important in building resilience against future weather-related disasters.

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The company calculates how much urban surface area is covered by “blue and green infrastructure” — including grass, trees, ponds and lakes — and how much is covered in “grey infrastructure,” such as concrete, pavement and buildings.

Its digital mapping tool allows cities to gauge the best use of available space — from rainwater harvesting to ponds and inner-city gardens — to boost sponginess, and to determine the risks of not doing so.

Arup’s most recent sponginess report — from 2022 — examined five African cities — Cairo, Durban, Kigali, Lagos and Nairobi — with Durban earning the second highest sponginess rating at 40%.

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