Check out the episode:

You can find the shownotes through this link.

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Are you interested in solutions for the urban heat island effect?

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Our summary today works with 5 articles and reports, titled Spatiotemporal variation of intra-urban heat and heatwaves across Greater Sydney, Australia, Mapping summer microclimates, Despicable urban places, Climate-smart playgrounds, and the Next generation cool-green car park concept for urban heat resilience co-authored by Sebastian Pfautsch, the next interviewee in episode 392, talking about his research and urban experiments to solve some of the challenges caused by urban heat.

Since we are investigating the future of cities, I thought it would be interesting to see how urban heat can be combatted with specific solutions. These resources advocate for integrating heat-responsive design solutions, such as permeable surfaces and natural shading, to create resilient and thermally safe public infrastructure in a warming climate.

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Welcome to today’s What is The Future For Cities podcast and its Research episode; my name is Fanni, and today we will introduce a research by summarising it. The episode really is just a short summary of the original investigation, and, in case it is interesting enough, I would encourage everyone to check out the whole documentation. This conversation was produced and generated with Notebook LM as two hosts dissecting the whole research.

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Speaker 1: cities all around the world are facing what is essentially a thermal siege. Mm-hmm. You’ve got global warming, pushing the bay, fine temperatures up, but then right where we live, the way we actually build our cities,

Speaker 2: all the concrete, the steel,

Speaker 1: exactly. All that dark asphalt. It’s trapping heat and creating this, this massive amplifier we call the Urban Heat Island effect, the UHI.

Speaker 2: And you’ve really hit on the critical point there. The problem is twofold. We’ve been handed this stack of research, a lot of empirical data, and it’s largely centered on greater Sydney in Australia. Right. It doesn’t just quantify this crisis, it shows just how quickly the whole risk is. Well, it’s accelerating.

Speaker 1: The acceleration is what is so alarming here. I mean, this isn’t some slow, manageable creep anymore, is it? We’re talking about a genuine thermal shift happening now.

Speaker 2: To put this into perspective for you, let’s just look at the history in the first 120 years of recorded weather for greater Sydney. That’s from 1859 all the way to 1979. The region saw 351 days where the temperature hit 35 degrees Celsius or more.

Speaker 1: So 35 degrees is what they call a hot day.

Speaker 2: That’s the threshold. Yes. So 351 of those days spread across more than a century.

Speaker 1: Okay. I’m with you

Speaker 2: now. You compare that whole span to just the last two decades,

Speaker 1: just 20 years.

Speaker 2: Just from 2000 to 2020. Sydney recorded 478 hot days.

Speaker 1: Wow. So more hot days in 20 years than in the previous 120.

Speaker 2: Far more. The frequency of extreme heat is skyrocketing and the projections are frankly sobering.

Speaker 1: What are they saying?

Speaker 2: The models suggest that by 2060, maximum air temperatures in Western Sydney could hit or exceed 35 degrees Celsius for a staggering 160 days out of the year

Speaker 1: 160. That’s basically the entire summer, and then some. You’re living in what we would now call a heat wave condition for months on end.

Speaker 2: It completely transformed summer from an annoyance into a chronic public health crisis.

Speaker 1: That’s really where this research goes, isn’t it? The health implications.

Speaker 2: It’s central to it. Extreme heat is the single most lethal weather risk in Australia. So we have these risk thresholds, like the hot day at 35 degrees, then an extreme heat day at 40,

Speaker 1: and then catastrophic

Speaker 2: and catastrophic at 45 degrees Celsius or more.

Speaker 1: But the danger isn’t just about those peak daytime highs, is it? Yeah. I was really struck by the data on nighttime temperatures.

Speaker 2: The daytime highs are, you could say, only half the battle, high nighttime temperatures, specifically when it stays above 25 degrees Celsius, right? That is a major, major contributor to heat related illness and mortality. Your body just can’t recover. It can’t cool down overnight. You wake up already in a state of heat stress.

Speaker 1: And what makes this so tricky for the public and for policy makers? Is that the official data, it often doesn’t tell the whole story does it? It misses the severity of the heat where people actually live.

Speaker 2: This is where the new research gets incredibly focused. You see the official Bureau of Meteorology stations, historically, they were often located in, well in ideal spots

Speaker 1: on cooler spots,

Speaker 2: cooler, greener, more vegetated areas. Think of the Royal Botanic Guardings in Sydney. And while those sites are great for tracking broad regional climate trends, they simply don’t represent the heat being trapped by urban density.

Speaker 1: But now with these new high density sensor networks, we can see the city’s thermal landscape in much greater detail,

Speaker 2: and the findings are stark. The data showed that central and southern parts of the city of Sydney had mean summer air temperatures up to 2.1 degrees Celsius higher than the northern and eastern sections.

Speaker 1: So the heat is really unequal. It depends on what your neighborhood is made of.

Speaker 2: It’s distributed according to land use on the really extreme days. These localized differences, they become. Frankly terrifying.

Speaker 1: There was one specific example right there

Speaker 2: was on one extreme heat day sensors recorded a temperature difference of nearly 14 degrees Celsius,

Speaker 1: 14 degrees between the coolest and warm spots in the same city

Speaker 2: at the same time. The coolest spot, the Royal Botanic Gardens. It was a manageable 28.2 degrees. Okay. The warmest, a heavily built up concrete dense area in a suburb called Rosebury hit 41.9 degrees.

Speaker 1: That 14 degrees swing is, I mean, that’s the difference between being a bit warm and being in a genuinely life-threatening environment.

Speaker 2: It’s a dangerous blind spot. Yeah. If you’re not measuring that microclimate risk, you can’t prepare for it. And the research highlights exactly which bits of our normal infrastructure turn into hazards

Speaker 1: like playgrounds.

Speaker 2: Playgrounds. Yes. The playground at the Juanita Nielsen Community Center hit a maximum of 39.2 degrees. It was the hottest place at the entire center that day. Hotter even in the streets nearby.

Speaker 1: And that brings us to the biggest culprit, the one the research has identified as the low hanging fruit heat source.

Speaker 2: That’s right. The ubiquitous at grade car park.

Speaker 1: This detail about car parks is just crucial. So let’s dig into why these seemingly benign areas are such heat factories. Here’s where it gets really interesting.

Speaker 2: It all comes down to three things really. SI exposure and material. Car parks are these massive unshaded continuous areas, and crucially, they’re almost universally covered in black asphalt.

Speaker 1: And that material has what we call a low albedo, which is just a fancy way of saying it absorbs almost all the sun’s energy.

Speaker 2: It’s like wearing a black t-shirt on a hot day, but magnified over thousands of square meters.

Speaker 1: And the survey numbers from Western Sydney were just. Staggering. 92% of car parks use this black asphalt.

Speaker 2: 92%. Yeah. And those surfaces reach astonishing temperatures. On a hot day, unshaded asphalt can routinely hit 69 degrees Celsius or even more,

Speaker 1: 69 degrees.

Speaker 2: There was this one powerful comparison in the sources. A strip of asphalt measured 62 degrees Celsius in full sun, okay? And just a few meters away, a grassed overflow area was a pleasant 28 degrees. That is a 34 degrees surface temperature difference

Speaker 1: on a mild day. Yeah. I mean, 62 degrees is hot enough to cause serious burns, and we just expect people to walk across these things

Speaker 2: we do. And that extreme surface heat, it dramatically affects the air right above it. But more than that. It changes what the human body actually feels.

Speaker 1: This is the, feels like temperature.

Speaker 2: Exactly. We call it tlo. The asphalt acts as a giant radiator just pumping that stored heat back out. Studies showed the feels like temperature above unshaded asphalt could be up to 10 degrees warmer than the measured air temperature.

Speaker 1: So if the air’s 35, your body feels like it’s 45 because of the heat coming off the pavement.

Speaker 2: Precisely, and that’s a critical difference for safety. And it gets worse the closer you are to the ground,

Speaker 1: which brings up a really sobering point about vulnerable people.

Speaker 2: A very serious risk for small children, people in wheelchairs, pets, anyone closer to the ground. The air temperature at about 30 centimeters above the asphalt was systematically up to one degree hotter than the air measured. Higher up at just over a meter,

Speaker 1: just because they’re closer to that scorching hot surface and there’s less wind.

Speaker 2: Exactly. And beyond that immediate risk, there’s a knock-on effect with emissions.

Speaker 1: From the cars themselves.

Speaker 2: Yes. When a car is parked on that surface, its interior can get past 64 degrees Celsius. So the driver gets in, blasts the air conditioning on maximum,

Speaker 1: and, and the engine has to work incredibly hard,

Speaker 2: which means noxious emissions peak for up to 20 minutes. Just shading the car parks could reduce both the health risk and that initial pollution surge.

Speaker 1: And the most astonishing part of all of this. For me was the policy vacuum. This massive dangerous heat. Liability is everywhere, and yet it seems no one is required to do anything about it.

Speaker 2: That’s correct. Current Australian design standards for car parks, they focus on dimensions, traffic flow, ventilation

Speaker 1: by many cars you can fit in

Speaker 2: right. There is absolutely no prescriptive guidance, no mandate to mitigate high temperatures. The guidelines might encourage a tree or two, but they don’t enforce the thermal performance needed. It’s a total blind spot

Speaker 1: that seems like the perfect place to start fixing things. So we’ve got the accelerating heat, the hot spots, the car parks. Let’s look at the toolkit. What can we actually do right now to transform these places?

Speaker 2: The fastest, simplest intervention is on the surface itself,

Speaker 1: modifying the surface

Speaker 2: exactly. Since asphalt is hot because of its low albedo, we fight that by applying high albedo materials. The simplest tool here is what they call cool pavements or surface coating.

Speaker 1: So this is literally just painting it a lighter color, A reflective coating

Speaker 2: in essence. Yes, it’s a highly reflective seal code that minimizes heat absorption, a simple color change during the heavy lifting. And the trial showed real promise.

Speaker 1: How much of a difference did it make?

Speaker 2: A significant one. The studies found these coatings reduced asphalt surface temperatures by an average of six degrees Celsius and in some cases up to 11 degrees.

Speaker 1: That’s a huge quick fix, but there was a really interesting caveat, wasn’t there an unintended consequence?

Speaker 2: There was. It illustrates the complexity here. While the reflective paint cools the surface itself, it can reflect that radiant heat sideways towards pedestrians.

Speaker 1: So the ground is cooler, but you feel hotter.

Speaker 2: The research caution that for people standing nearby, it can make the air feel up to three degrees warmer. So it’s a great fix for the parking bay, but maybe not for the sidewalk right next to it.

Speaker 1: Okay, so if we can’t always paint it, the next option is to replace the surface entirely with something permeable.

Speaker 2: Exactly. Replacing solid asphalt with things like porous asphalt, interlocking pavers, even grass pavers. It serves two purposes.

Speaker 1: It holds less heat

Speaker 2: and it lets water through, which connects to what we call water sensitive urban design,

Speaker 1: right? WSUV.

Speaker 2: When you retain water in the ground, you enable evaporative cooling. The energy is used to turn liquid water into vapor, which pulls heat from the environment. It’s something standard. Asphalt actively prevents.

Speaker 1: So surface solutions are critical, but you can’t talk about cooling without talking about shade. It’s the most effective tool we have.

Speaker 2: Trees are the gold standard. The long game, they provide shade and they cool through transpiration, but the data shows that trees take time. A long time, a very long time. Newly planted trees, even six years after construction can still have small crowns. They aren’t providing the shade we need right now to combat this accelerating heat,

Speaker 1: which leads us to this really impressive prototype. They studied the next generation green car park.

Speaker 2: This is such a superb idea. It integrates biology and engineering. You grow fast-growing vines on trellis support structures,

Speaker 1: creating an instant green roof over the parking spots, and

Speaker 2: you bypass the decade plus, you’d have to wait for a tree to mature

Speaker 1: and did it work as well as it sounds,

Speaker 2: it worked extremely well in a case study at a place called Huro Gardens. The shade from these young vines reduced the asphalt surface temperature by 50%. 50%.

Speaker 1: That’s jaw dropping

Speaker 2: on a hot afternoon. It took the surface from nearly 60 degrees Celsius down to just below 30.

Speaker 1: That’s transformative. Just with some green shade

Speaker 2: and they had a specific design tip. They recommend positioning these structures on the western boundary of the car park to maximize that afternoon cooling when the sun is at its most intense.

Speaker 1: What about beyond the car park? The density core, where you can’t just build a huge trellis

Speaker 2: for those high density areas. You need other forms of green infrastructure. Things like green roofs and green walls, and

Speaker 1: they really help.

Speaker 2: They do. Green roofs can reduce surface temperatures by up to 30 degrees. Green walls are even better for air cooling at street level, reducing air temps by two to five degrees. They also looked at things like Milwaukee pocket forests.

Speaker 1: These are those super dense native plantings.

Speaker 2: Yes, they accelerate canopy cover in small spaces. It’s about finding the right tool for the right, very tight space.

Speaker 1: The sources also got into using water, specifically irrigation in parks. And the results there were a bit mixed.

Speaker 2: They were complex. It wasn’t a silver bullet. They compared an irrigated park to a non-irrigated one. And surprisingly, the irrigated park was often a tiny bit warmer.

Speaker 1: So just adding water isn’t the guaranteed fix.

Speaker 2: It suggests that the existing tree shade of the surrounding buildings were more dominant factors than the water alone, at least in that spot. However, another study did show a consistent cooling effect from irrigation.

Speaker 1: So context matters.

Speaker 2: Context is everything. It seems to be a viable strategy, but only when it’s implemented correctly alongside a really robust tree canopy.

Speaker 1: Okay, and finally, there’s the resilience plan for when a catastrophic heat day is unavoidable. The idea of climate shelters,

Speaker 2: we need safe places for people to go. Actively cooled public spaces. The studies looked at air conditioned community centers and found they provided consistent life-saving relief.

Speaker 1: How much cooler were they inside?

Speaker 2: Often 10 to 15 degrees cooler than the outside air. At one center, the reception area was 28 degrees Celsius when the rooftop temperature was hitting 41.4.

Speaker 1: That is a genuine lifesaving difference.

Speaker 2: It is. So the critical recommendation from this is that any center designated as a heat refuge, especially older ones that might not have it. Must urgently install air conditioning and crucially backup up power systems

Speaker 1: to make sure they can function when the grid is strained.

Speaker 2: Exactly.

Speaker 1: If we connect this to the bigger picture, we started with this harsh reality of accelerating under-reported heat. It’s concentrated in the gray expanse of our cities, especially these unshaded car parks,

Speaker 2: and we found a powerful data-driven toolkit. Everything from quick fixes, like reflective coatings to that really innovative cool green car park prototype, the solutions exist, right? And the key lesson is that urban cooling requires a multi-pronged approach. You need the trees for the long game. You need the right materials for the surfaces, and you need those safe indoor refuges as a resilience plan. But implementing all of this is being held back by outdated policy.

Speaker 1: So what does this all mean?

Speaker 2: We’ve seen that the highest, most dangerous surface temperatures are on infrastructure, like asphalt, car parks, and playgrounds, spaces that are integral to daily life for commuters, for children. And right now, design policy prioritizes the car. Its dimensions and its flow. Over human thermal safety.

Speaker 1: So here’s the provocative thought.

Speaker 2: Should the protection of vulnerable people now legally supersede the requirements for parking space dimensions in our building codes, should that make passive large scale cooling strategies like that green car park prototype, the absolute minimum standard for all future urban development? Because that change needs to happen faster than the climate is warming.

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Episode and transcript generated with ⁠⁠Descript⁠⁠ assistance (⁠⁠affiliate link⁠⁠).