Auckland is the world's 'spongiest' major city, but what does that mean?

Auckland is estimated to be the major city most able to effectively absorb torrential rainfall today, thanks to its numerous parks and water bodies. Photo: AFP

Building the resilience of large cities to climate change – bringing extreme heat and heavy rainfall – will require more green space and less concrete, according to a report from Arup.

The British consulting firm estimates that Auckland is the major city most able to effectively absorb torrential rainfall today, thanks to its numerous parks and water bodies.

One of the major threats of climate change is the increase in intense rainfall. But are large cities prepared for this?

To answer this question, Arup set out to analyse the soil quality and terrain of seven major cities around the world: Auckland (New Zealand), London (England), Mumbai (India), Nairobi (Kenya), New York (US), Shanghai (China) and Singapore.

As things stand, the New Zealand city appears to be the most capable of absorbing such heavy rainfall. Conversely, London is the least prepared in this line-up.

Beyond this study, Arup hopes to make cities aware of the means that can be used to fight against these natural phenomena, which are more and more recurrent.

In each of these cities, a sample of 150sq km of terrain was studied in order to judge each one's capacity to adequately absorb heavy rainfall.

In Auckland, half of the area studied was made up of green space (parks, gardens, etc) and blue space (waterways, ponds, etc), which allowed it to obtain the highest "sponginess" score.

Note that Nairobi has even more green-blue areas, but the city's soil is less permeable than in Auckland.

In comparison, Shanghai and London are much more "concrete" cities, especially in their centres. New York comes just ahead with the most permeable soil type of the cities studied, and also with many green spaces (other than Central Park).

Overall, Auckland's urban centre is rated as 35% "spongy", ahead of Nairobi (34%), Singapore, Mumbai and New York (30%). Next are Shanghai (28%) and London (22%).

In the future, large cities will have to learn to deploy nature-based solutions rather than continue to focus on concrete urban centres. Even the most "spongy" cities must seek to improve and work with nature to provide maximum resilience.

The term "sponge city" was coined in 2013 by Peking University professor, Kongjian Yu, to describe cities that work with nature to properly absorb rainwater, instead of using concrete to channel it. – AFP