How to turn down the heat on Auckland’s streets

By Jamie Morton

It might have been Auckland but, as one meteorologist put it, it felt like Fiji.

Amid what was New Zealand’s hottest summer on record, in 2017-18, Auckland sweltered through nearly 50 days where temperatures climbed above 25C.

Beaches and public pools filled with Aucklanders trying to escape the heat, while department stores sold out of fans and a rare 115-hour period of muggy nights caused widespread sleeplessness.

For Aotearoa’s largest city, that run of scorching temperatures also offered a glimpse of a warmer future, where extra-hot days will compound what’s called the urban heat island effect.

This is where built-up metropolitan areas – like the concrete and asphalt canyons of central Auckland – absorb and trap heat all day and night.

“Because the heavily paved surfaces of cities absorb a lot of the sun’s radiative heat, it means that we not only have a lot of it coming in, but that it also lingers there, before slowly radiating back,” explains University of Auckland urban planning expert Dr Tim Welch.

“A pavement on a sunny day can heat to something like 65C or greater, simply because it’s absorbing that heat all day long.”

In a given urban area, where heat-retaining materials can make up nearly half of surfaces, the effect can warm local air temperatures by as much as 7C.

While Auckland’s coastal setting and ocean breezes have traditionally taken the edge off summer heat, that natural buffer is diminishing as the climate warms.

The city’s average temperature is already at least 1.6C higher than a century ago, and the number of hot days above 25C – now around 21 each year – is projected to climb to nearly 80 days by the end of the century.

Auckland Council is planning under a severe-warming scenario of 3.8C, acknowledging that earlier models underestimated the pace of change.

Welch adds that humidity – long a sticky signature of a typical Auckland summer – brings another dimension to the challenge.

“The more humid it is outside, the less effective our own natural systems are with dealing with heat, leaving fewer ways for us to cool ourselves.”

Recent studies have been telling us more about what this heat means for public health.

An Auckland Council-commissioned report, for instance, found the city centre experiences a night-time UHI effect with temperatures up to 3C warmer than surrounding rural areas.

Council-adopted projections indicate a 3C rise in global temperatures could lift Auckland’s annual heat-related deaths from around 14 to 88.

As the population ages, and older people remain most at risk during extreme heat, that vulnerability is likely to grow.

Other groups likely to bear the burden most heavily include children, people with pre-existing health conditions, renters, and those in low-income areas with limited access to shade, insulation or cooling.

“Just a couple of degrees celsius change in temperature can have a significant impact on those populations,” Welch says.

How other cities are meeting the heat

International cities – many of which are older, more densely built, and not as naturally buffered as Auckland – are already taking bold steps to lessen the urban heat island effect.

Welch singles out some examples from Europe and North America, where cities are facing the twin challenge of historic, narrow infrastructure combined with more severe, prolonged heatwaves.

Paris, for instance, is removing up to 70,000 on-street car parks to increase cooling green space, while Amsterdam has been systematically taking out thousands of car spaces and prioritising green infrastructure in its low-lying environment.

Barcelona is executing its decades-long ‘superblock’ plan that fundamentally restructures its city blocks to reduce the need for pavement, boost walkability, and integrate green spaces.

Japan, which has a large older population, has prioritised replacing surface parking with turf and increasing tree cover.

Melbourne has been transforming some of its streets and laneways into shaded green corridors that cool neighbourhoods, while encouraging walking and cycling.

Welch argues that Auckland and other New Zealand urban centres are well positioned to follow suit, and can turn their smaller scale into an advantage.

He points out that implementing green infrastructure is simply more cost-effective than continued reliance on heat-absorbing surfaces.

“People say we can’t do it here in New Zealand because we don’t have as many people,” he says.

“But the reality is, because we have fewer people, it means we have a lower demand for things like parking – while green solutions are actually a lot cheaper than building cement, pipes and pavement everywhere.”

Plan for Auckland

Welch says Auckland’s solution lies in reversing a decades-long trend of paving and building over natural surfaces – or what he calls going from “grey to green”.

It also requires sustained attention and clear investment priorities: a process that Auckland has already begun.

The first step, he says, is addressing the unnecessary footprint of the car – particularly redundant parking, one of the biggest heat island contributors.

“There are a lot of opportunities that many cities have identified to reduce the number of car parks with materials that are better at absorbing water and reducing heat.”

Such shifts yield multiple, compounding benefits, whether through more natural shading that reduces heat stress and energy costs, increased infiltration that manages stormwater runoff, or enriched vegetation that boosts urban biodiversity.

Research shows replacing asphalt with grass or permeable materials can cut surface temperatures by around 12C, while tree canopy can feel up to 17C cooler than open sun.

Even modest green retrofits overseas have delivered measurable results: one study in Japan found grass-covered parking areas up to 14C cooler than asphalt equivalents.

The economic case for the transition is similarly compelling, says Welch, citing analyses that suggest each dollar spent on greening infrastructure brings a four-fold benefit, through savings on building energy use and stormwater management.

“And that’s even without considering the massive health benefits.”

For its part, Auckland Council is moving ahead with its Urban Ngahere (Forest) Strategy, which aims to increase tree canopy cover from 18 to 30 percent by 2050.

The council’s recently published Urban Heat Assessment also provides high-resolution maps that pinpoint the city’s worst heat pockets.

This data is helping guide where green infrastructure can be invested, while accelerating the exploration of other ‘blue-green’ solutions, including urban wetlands and the use of more permeable materials for footpaths.

Welch says this approach could go even further.

Auckland’s 7800km of roads reimagined as cooling corridors lined with trees, rain gardens and permeable paths, transforming everyday transport routes into part of the city’s heat-mitigation network.

The council’s targeted efforts already mean thousands of trees are being planted on public land in parks and berms, specifically prioritising low-cover neighbourhoods like parts of South Auckland.

Welch expects that taking ‘needs-based’ action will only become more important as heatwaves become more severe and frequent.

Just as critically, he adds, is ensuring there is ongoing political will to act – which means being proactive rather than reactive.

“The difficult thing is that we often just don’t think about this stuff until it’s too late,” he says.

“The success that we’ve seen around the world comes from that kind of proactive thinking – it’s saying, let’s address this before it becomes a problem.”

• The world is facing unprecedented environmental challenges. Planetary Solutions, an initiative of the Sustainability Hub at Waipapa Taumata Rau, University of Auckland, and Newsroom, explores these issues — and the practical ways we can all be part of the solution.