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Auckland recently scored highest in a ranking of the 'sponginess' of seven global cities (Credit: S E Barbour/Getty)

Cities want to grow to be greater ‘spongy’. Auckland is main the way.


Tangled mats of muddy flora line the footpaths of Underwood Park, a slim stripe of inexperienced winding alongside a creek underneath the small volcanic cone of Ōwairaka (Mt Albert) in Auckland, New Zealand. In the water, clumps of sticks and the occasional plastic bag are marooned on sticking out rocks and branches.

A iciness hurricane swept thru the town overnight, losing heavy rain, and Te Auaunga (Oakley Creek), one of the town’s longest city streams, has overflowed its banks.

“But that’s alleged to happen,” says Julie Fairey, chair of the Puketāpapa nearby board, who’s displaying me round Underwood and the neighbouring Walmsley Park.

The related parks are designed to gather extra stormwater, soak it up like a sponge, and slowly launch it again into the creek. The debris left at the back of is proof this “mystery infrastructure” is working, Fairey says. The parks are flanked on each aspects via way of means of public housing developments. “This stuff is designed to flood in order that the houses don’t,” she says.

The researchers calculated that 50% of Auckland’s floor turned into inexperienced or blue, even after aside from its harbours

It wasn’t continually this way, Fairey tells me, as we watch a black shag drying its wings on a rock. Less than a decade ago, the waterway turned into a concrete-covered culvert that ran thru seldom-visited muddy fields. When it flooded, water sloshed into the encircling suburbs. It accrued engine oil, sediment and garbage and sucked this dangerous aggregate out into the town’s well-known harbour, rendering the beaches dangerous to swim.

But in 2016, paintings commenced to loose Te Auaunga from inflexible concrete, and repair it to a greater herbal, meandering shape. Its banks at the moment are lush with local flora like harakeke (flax) and tī kouka (cabbage trees), in addition to reeds, ferns and different filtering wetland plants.

The adjustments have improved this a part of the town’s capacity to soak up extra rainfall, an characteristic occasionally called “sponginess”. Auckland turned into currently named the maximum spongy worldwide town in a report via way of means of multinational structure and layout company Arup, way to its geography, soil type, and concrete layout – however professionals warn it is able to now no longer lead the % for long.

As weather alternate intensifies intense climate occasions worldwide, what can different towns study from Auckland’s successes – and failures?

The godfather of the “sponge towns” concept is Peking University panorama structure professor Yu Kongjian, who almost drowned in a flooded river as a child, however controlled to tug himself to protection via way of means of grabbing keep of the willow branches and reeds that fringed its banks. In 2013, as an city designer, he proposed that towns use nature in preference to concrete to gradual down heavy rain – an idea now being applied in towns throughout China and gaining interest across the world.

As the planet warms, excessive rainfall and flash flooding is anticipated to drastically boom. The spongier a town is, the greater resilient it’ll be withinside the face of the ones threats. “As our weather receives greater intense, we have got were given to deal with growing hazards,” says Mark Fletcher, worldwide water chief at Arup and co-writer of the company’s “spongy town” report.

Fletcher and his colleagues discovered that Auckland turned into the spongiest of 7 worldwide towns, marginally outscoring – so as of sponginess – Nairobi, Singapore, Mumbai, New York City, Shanghai and London.

A town that sits low at the rating like London, it simply approach you need to attempt a bit tougher to construct a few sponginess in – Mark Fletcher

The group mapped the percentage of grey (concrete and buildings), inexperienced (flora) and blue (ponds and streams) withinside the seven towns the use of Geographic Information Systems (GIS) technology, satellite tv for pc imagery and system learning. It then mixed those maps with statistics approximately soil sorts and runoff ability to discern out each town’s herbal absorbency.

Low-lying, coastal Auckland is New Zealand’s biggest town, with a populace of 1.four million people and an annual common rainfall of 1210mm (48in) – barely greater than New York, and two times as a lot as London generally gets in a year.

The researchers calculated that 50% of Auckland’s floor turned into inexperienced or blue, even after aside from its harbours (London had the least of the seven towns, with 31%). In an excessive rainfall occasion – 50mm falling in 24 hours – they expected that 35% of the water falling on Auckland might be absorbed into those spongy blue and inexperienced parts, leaving 65% that could should be handled via way of means of engineered stormwater systems – otherwise overflow and flood.

“It’s a degree of how that town turned into developed, and its center underlying herbal morphology,” says Fletcher.


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Nairobi got here a close second, at 34% spongy. The Kenyan capital has even greater inexperienced and blue areas than Auckland – specifically parks and concrete backyards – however better run-off ability because of its clay-dominant soils, which soak up much less water than sand or gravel. In the lowest-ranked town, London, simply 22% of the water in a comparable rainfall occasion might be absorbed – a hazard highlighted in actual lifestyles in July 2021, when 47.8mm of rain fell in a single hour, causing enormous flooding of roads, homes and Tube stations.

Kathy Waghorn, an city researcher on the Auckland University of Technology’s School of Future Environments, isn’t always amazed that her town turned into rated as extraordinarily spongy. “We’ve were given low city density, we nevertheless have a variety of single-level dwellings, we nevertheless have gardens,” she says.

Auckland’s geomorphology performs a function too, she says: the slim strip of land enfolded in large harbours, the handfuls of small dormant volcanoes dotting the town, the streams strolling down their inexperienced aspects, and underneath them, the legacy of their lava – basalt and scoria caves and sinkholes. “The volcanic discipline has fashioned a number of that open space,” Waghorn says. “Even our stone is type of spongy.”

But Waghorn and different researchers are worried that Auckland will now no longer maintain its crown for long.

A package deal of long-term tendencies all factor toward the town turning into drastically much less absorbent, even as weather alternate will increase the variety of intense rainfall occasions and the hazard of flooding. (In Auckland, for each diploma of worldwide warming, the depth of short-period storms is projected to boom via way of means of 14%.)

For starters, there is strong political pressure for city intensification withinside the town. New Zealand has some of the least low-cost housing in the OECD,  and housing call for is focused in Auckland.  The New Zealand authorities has currently signalled sweeping adjustments to making plans rules that are in all likelihood to prompt “a alternate in density and peak throughout a super deal of the isthmus”, says Waghorn. “The spongy suburbs that we have got were given will disappear, due to the fact there will be loads greater impermeable floor – greater housing, greater driveways and parking areas.”

The call for for housing has additionally induced government and builders to eye up different massive inexperienced spaces like golfing courses and racecourses, which have a tendency to be in prime residential locations, Waghorn says. Some have already been sold, and plans made to construct heaps of recent houses at the once-inexperienced space.


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