There are practical, science-backed steps councils can take to help cool our cities as summers get hotter. University of Auckland Senior Lecturer Timothy Welch explains.
Stand on any car park on a sunny day in February and the heat will radiate through your shoes. At 30C air temperature, that asphalt hits 50–55C – hot enough to cause second-degree burns to skin in seconds.
Right now, in the northern hemisphere summer, 100 million Americans are dealing with 38C temperatures. Britain is preparing for hundreds of heat deaths. In New Zealand, of course, we’re still lighting fires and complaining about the cold.
But that gives us time to prepare for our own heatwaves. Open-air car parks that sit empty for 20 hours a day could become cooling infrastructure instead. Transport routes can become cooling corridors.
Replace asphalt with trees, grass and permeable surfaces, and you can drop surface temperatures by 12°C. It’s not complicated. It’s not even expensive.
It’s getting hotter
NIWA data shows New Zealand is already experiencing extreme temperatures five times more frequently than historical baselines. Wellington hit 30.3C and Hamilton 32.9C in January, both all-time records. Marine heatwaves are persisting around South Island coasts months longer than usual.
Aucklanders will face 48 additional days above 25C annually by 2099, as summer temperatures increase by 3.6C. Auckland Council has already adopted the most severe warming scenario (3.8C) for infrastructure planning, acknowledging previous models underestimated the pace of change.
Even Wellington’s famously cool winds won’t offset the estimated 79% increase in residential cooling energy demand by 2090, driven by hotter, longer summers and more extreme-heat days.
A quarter of New Zealand’s population will be over 65 by 2043, an age when heat regulation becomes harder and fixed incomes make cooling costs a real burden.
Currently, 14 heat-related deaths occur annually among Auckland’s over-65 population when temperatures exceed just 20C. As the mercury rises, our older population will be at a greater risk.
Greener is cooler
While global average temperature increases of 1.5C might appear modest, the actual temperatures we experience in our cities is far more extreme. The built environment – all that concrete and asphalt – traps heat like an oven.
But converting car parks back to green space can knock the temperature down dramatically.
Research from Osaka Prefecture in Japan recorded surface temperature reductions of up to 14.7C when comparing asphalt to grass-covered parking during sunny summer conditions.
Another study found temperature differences averaging 11.8C between asphalt and grass surfaces, with air temperature differences of 7-8°C at human height.
Trees are the heavy lifters here. Stand under a tree on a hot day, and it can feel 17C cooler than standing in the sun. Add rain gardens (shallow, planted areas designed to capture and filter stormwater) and ground cover for another 2-4C reduction. Layer these elements together, and you get cooling that works even on overcast days.
Roads as cooling corridors
Grassy and tree-covered car parks are just a starting point. Auckland’s 7,800 kilometres of roads could become the city’s cooling system. Every bus lane, cycleway and walking path is an opportunity for green infrastructure.
If we stop thinking of transport corridors as merely a way to get from one place to another, and see them as multifunctional cooling networks, the possibilities multiply while the costs remain relatively low.
Melbourne’s COVID-era parklet programme proved this works: 594 small conversions created 15,000 square metres of public space at just A$300–900 per square metre.
Converting even a small percentage of New Zealand’s parking infrastructure could create connected cooling corridors throughout our cities.
Protecting cycleways with a tree canopy would encourage active transport while cooling neighbourhoods. Bus lanes with rain garden medians would improve service reliability while managing stormwater.
5 things councils can do
Summer is six months away – maybe not enough time to do all the work needed, but certainly enough to get a plan in place. Here are five things councils could do.
- Plant trees now: winter is planting season. Focus on car parks and heat-vulnerable neighbourhoods. Use fast-growing natives and protective rings to ensure survival. Trees planted now will provide shade by December.
- Install modular planters: test cooling locations with movable infrastructure before committing to permanent changes. Order now for spring placement when residents can see the benefits.
- Schedule paving replacements: when resurfacing is needed, switch to permeable options and get heat-reducing surfaces in place before summer.
- Design shade structures: plan and budget pop-up shade for the hottest areas. Having designs ready means quick installation when temperatures spike.
- Organise spring planting days: line up community groups now, source trees through winter nursery contracts, and hit the ground running in September. Small investments in coordination yield big cooling dividends.
Auckland Council’s $1 billion climate action package includes grants of $1,000 to $50,000 for climate projects. Wellington’s Climate and Sustainability Fund and Christchurch’s 50-year Urban Forest Plan provide similar frameworks.
The Ministry for the Environment’s National Policy Statement on Urban Development creates opportunity by removing minimum parking requirements. This frees up land for trees, gardens and public spaces instead of underused asphalt, maximising climate co-benefits: cooler surfaces, better stormwater management and more pleasant streetscapes.
By next February, we can either be thanking ourselves for planting trees and converting car parks, or feeling the heat from that 50C asphalt.
Author Timothy Welch is a Senior Lecturer in Urban Planning at the University of Auckland, Waipapa Taumata Rau.
This article is republished from The Conversation under a Creative Commons license.
