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Research reveals potentially dangerous ‘urban heat island’ effect in central Auckland

Research reveals potentially dangerous ‘urban heat island’ effect in central Auckland

Stylized illustration of the sun shining on the parked car and the trees creating shadow

Photo: RNZ

The central city of Auckland can get up to three degrees warmer at night than other parts of the region due to the urban heat island effect, new data shows.

Research commissioned by Auckland Council They also found large temperature differences between locations within a few blocks of each other, with areas with many hard surfaces tending to record the highest average temperatures.

While New Zealand is not currently experiencing the same heat extremes as places like Australia or parts of Europe, climate change researchers say there are still health risks, which will worsen as global temperatures rise.

“With the climate getting warmer, we know the heat will be more frequent, with more hot days and heatwaves, when in reality we haven’t experienced them much before in Auckland,” said council’s chief climate resilience adviser Petra Pearce.

Currently, the temperature reaches 25°C in Auckland about 20 days a year. At the end of the century, expected to increase to 90 days a year.

The heat research, carried out by engineering consultancy Arup, divided Auckland into hexagons measuring about 300 meters wide – the equivalent of one or two city blocks – and took into account wind patterns, surface coverage such as trees, grass and concrete, and the density of buildings and materials.

Temperatures were modeled over a five-month summer period, using global climate data from 2021-2022 (Auckland’s hottest summer on record). The researchers then compared them to actual temperatures collected by NIWA weather stations across the region during that time.

The highest average temperature, 19.8°C, was recorded in Auckland’s central business district, on a block of Nelson Street that has the highest proportion of concrete and other impervious surfaces in the city centre.

Even at night, this area remained much warmer, recording an average minimum temperature of 17.2°C, compared to 15.6°C in Albert Park, a central city park just a few hundred meters away. this.

“Some of the results found that the city center was up to three degrees warmer than surrounding rural areas at night during this assessment period, and they also found that there were differences within the city, up to three degrees during a peak temperature day.”

Parts of southern Auckland also recorded uniformly high average and maximum temperatures, while the coldest parts of the region were the Waitākere and Hunua ranges, and coastal peninsulas such as Whangaparāoa and the North Shore.

“We’re a coastal city and we have a lot of bodies of water around us, so we get ocean breezes during the afternoon on those hot summer days and that actually moderates some of our urban heat,” Pearce said.

“You can see that the coastal border is usually colder than inland.”

Map of Auckland showing the different average daily temperatures across the region


Photo: RNZ / Kate Newton

Maximum daytime temperatures tended to be higher in grassy rural areas outside Auckland city, which the researchers suggested was due to low humidity levels during the summer.

A map showing how the daily maximum temperature varies in Auckland's CBD

Heat data provided by Auckland Council
Photo: RNZ / Kate Newton

The Great Barrier Island also showed warm average and nighttime temperatures.

Pearce said that’s because the island has a warmer climate than the rest of the region and warmer sea surface temperatures, which affects land temperatures.

A map showing how the daily minimum temperature varies in Auckland's CBD

Heat data provided by Auckland Council
Photo: RNZ / Kate Newton

The urban heat island effect is a common phenomenon in urbanized areas around the world.

“It’s more pronounced at night than during the day because hard city surfaces, like concrete roads and buildings, for example, retain that heat during the day and release it at night,” Pearce said.

The amount of green cover, which provides shade and cooling through a process called transpiration, was markedly different in Auckland, he said.

“Some parts of the city are very green and others, particularly southern Auckland, have very low tree canopy cover… So what you see when you see a lot of warmer areas in the southern part of the city “It’s the lack of green spaces.”

Heat was an “underestimated” risk in New Zealand, said Luke Harrington, a professor and climate change researcher at the University of Waikato.

“We have to remember that extreme heat is the deadliest type of climate hazard around the world. Even if we look at places that are considered colder climates, there are still periods of relatively extreme heat that can kill people, and that This is also the case in New Zealand.”

A study published last year estimated that 500 children under five are hospitalized in New Zealand each year for heat-related reasons, Harrington said.

“If you think about expanding that to all age groups, and particularly older ones, that number would increase again.”

People with pre-existing cardiovascular problems were also at risk, because prolonged extreme heat placed additional stress on the heart, he said.

Other New Zealand research has estimated that heat-related deaths among older people could rise from 14 a year to 88, with a three-degree rise in global temperatures.

The urban heat island effect could be particularly dangerous during a heat wave.

“If you don’t cool down, then your body doesn’t have a chance to have that breather before you start the next day,” Harrington said.

“So when you have this urban heat island effect that exacerbates those nighttime temperatures, it further amplifies the potential risks from a health perspective.”

Extreme heat was the most rapidly changing extreme weather around the world, but Auckland and other parts of New Zealand were “pretty ill-equipped” to deal with it, he said.

“At the moment we haven’t thought about this at all, because I think there’s still a view that we’re not actually that vulnerable in New Zealand.”

Beachgoers enjoy the sunset at Bondi Beach during a heatwave in Sydney on December 19, 2019. A state of emergency was declared in Australia's most populated region on December 19 when a heatwave without precedents fueled wildfires out of control, destroyed homes and suffocated large areas. with toxic smoke. (Photo by FAROOQ KHAN / AFP)

Heat waves can be deadly, killing half a million people each year and hospitalizing many more, according to research by the World Health Organization.
Photo: AFP / Farooq Khan

Creating a formal heat warning system, similar to the heavy rain warning system Metservice already operates, would be an important step, combined with clear health advice, Harrington said.

“A lot of this just comes from behavioral messages…Often it’s pretty simple things, like not exercising during the peak of the day, making sure you stay hydrated.”

It was also important to identify which groups in a city or community were most at risk and come up with a plan to protect them during periods of extreme heat, he said.

auckland already has a heat vulnerability indexdeveloped in 2019, showing that parts of South and West Auckland are the most vulnerable due to their demographics.

Petra Pearce said other options the council was considering or implementing included more blue-green infrastructure such as urban wetlands and green roofs, planting more shade trees – especially in south Auckland – and using more permeable materials to build footpaths and other hard surfaces.

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