Cities are vulnerable to heatwaves. But green spaces can help more than we thought

[hauntedheadnc]

Cities are vulnerable to heatwaves. But green spaces can help more than we thought
ZME Science

It’s not just that the planet is getting hotter; cities are getting much hotter than their surroundings. In fact, urban heatwaves have become a common occurrence, affecting 1.7 billion people. In Europe alone, the 2023 heatwave killed over 61,000 people. Now, a new study by researchers in the UK shows how much green interventions can help cool down cities.

***

The cooling effect of green infrastructure varies depending on multiple factors (including local climate, the species involved, etc). But the effect is pronounced. Botanical gardens are, on average, a whopping 5 degrees Celsius cooler than their surroundings. Even a street tree cools its immediate surroundings by almost 4 degrees. This is how much different types of green infrastructure can reduce local temperatures:

In general, the team found that the bigger the park (or any other green infrastructure), the bigger the benefits. Furthermore, if parks are linked together via green corridors, there’s also a compound effect.

[jmecklenborg]

Breaking news: it's cooler in the woods during the summer than outside the woods.

[Yuri]

Originally Posted by jmecklenborg

Breaking news: it's cooler in the woods during the summer than outside the woods.

I guess the point here is as heat waves and extreme heat events are becoming common places, people will look more for green spaces, tree lined streets more and ignore the downsides (falling trees due storms).

That's certainly the case here in São Paulo: the city has a pathetic low number of green spaces but several districts are full of tree lined streets. São Paulo was notorious for its milder summers (hottest month had 18oC min and 27oC max average). Now, the averages are good 3oC above and people will certainly seek for shades more often.

[hauntedheadnc]

Originally Posted by jmecklenborg

Breaking news: it's cooler in the woods during the summer than outside the woods.

You don't say? Well, I can't imagine why someone would have taken the time to study something so obvious, and come up with an actual temperature range -- seems like a dreadful waste of time to know exactly how much a street tree can affect the temperature of the surrounding area.

Now be nice, or else I'll start posting photos of the Nashville skyline and you'll end up blinded or driven insane at the very sight. Don't think I won't do it either.

[Steely Dan]

We planted a black oak sapling in the parkway in front of our building last summer.

Gonna take a while (couple decades) before it's casting any meaningful shade, but hey, you gotta start somewhere.

And once they get going, these black oaks can really go the distance.

My kids' school grounds a block south of us has three GIGANTIC black oaks from the before times. They brought in a tree dude who estimated that they're all 200-250 years old!! There wasn't even a Chicago yet when they first sprouted outta their acorns.

I hope the black oak we planted can go 200+ years.

[jmecklenborg]

Originally Posted by hauntedheadnc

You don't say? Well, I can't imagine why someone would have taken the time to study something so obvious, and come up with an actual temperature range -- seems like a dreadful waste of time to know exactly how much a street tree can affect the temperature of the surrounding area.

Many US cities have woods and big trees all over the place, and not as part of some plan endorsed by Twitter or wherever this article came from. Trees aren't a new idea.

Also, many poor Americans don't understand nutrition/hydration and refuse to drink water and/or electrolytes while working in the heat or while just sitting around. You can't teach them otherwise.

[mousquet]

Originally Posted by jmecklenborg

Trees aren't a new idea.

No one said it was new. We're just talking about the significance of trees in urban planning here. That's an important topic in cities whose urban fabrics are very dense.
When we discussed it on the French forum, we noted a couple of difficulties about growing more trees in town.

1. Developers often see greenery as a waste of room. They'd rather build more condos to increase their turnover and profits.

2. Some municipalities would be a little reluctant at the thought of more gardens in the public realm, because it means more expense to them. You need to pay for gardeners to maintain green spaces.

Everybody knows about the benefits of trees cause it's quite obvious indeed, especially in a time when heatwaves will be more and more frequent.
But then, you have to deal with particular interests that don't necessarily advocate greenery in their projects.

[hauntedheadnc]

Originally Posted by jmecklenborg

Many US cities have woods and big trees all over the place, and not as part of some plan endorsed by Twitter or wherever this article came from. Trees aren't a new idea.

The article came from ZME Science which, according to an organization that would know, knows more about the issue than you do. So you can stop being petty and harumphing about the topic like an offended old spinster any time you like. Nobody said trees were a new idea. We know they aren't. No shit, Sherlock, as some would say, even.

What is new though, is to be able to work the quantified benefits of trees and greenspace into costs and projections, and to maximize their impacts in architecture and urban design. To, for example, be able to figure out exactly how many trees it would take, and what kind, and where they should be placed, to appreciably cool the Place de l'Opera in Paris.

And correct me if I'm wrong, things like that are what we're here on this forum to discuss.

Also, many poor Americans don't understand nutrition/hydration and refuse to drink water and/or electrolytes while working in the heat or while just sitting around. You can't teach them otherwise.

Well, you've convinced me. I, too, am now offended by the presence of trees in urban areas, and I'm even more offended that anyone would try to quantify their benefits in the built environment. How dare they? Have these so-called "scientists" no decency?

[Nouvellecosse]

Originally Posted by hauntedheadnc

Well, you've convinced me. I, too, am now offended by the presence of trees in urban areas, and I'm even more offended that anyone would try to quantify their benefits in the built environment. How dare they? Have these so-called "scientists" no decency?

I think he just means that people who fall within a broad income or class category are all the same and are incapable of comprehending basic health and nutrition concepts due to their inherent inferiority. Yay science!!

[jmecklenborg]

Originally Posted by hauntedheadnc

The article came from ZME Science which, according to an organization that would know, knows more about the issue than you do. So you can stop being petty and harumphing about the topic like an offended old spinster any time you like. Nobody said trees were a new idea.

I own a bunch of mature trees, maybe 50 of them. Some of them overhang my houses, both of which are over 100 years old. I also own two lots with a variety of mature trees on them, one of which has been bothering me for several years as it overhangs a neighboring business and no doubt drops a ton of leaves into their gutters. They haven't complained so I haven't done anything about it.

I can tell you that modern houses with no tree cover are more comfortable during the summer than are either of these old houses. A lot of old houses are charming but they have serious problems that can't be fixed without a gut rehab, and that rehab will almost certainly ruin much of their charm.

We are also, of course, blaming the trees or buildings instead of the individuals for doing logical things like drinking water instead of pop and beer when it's hot.

People also do completely irrational things like run window AC units AND their furnace at the same time. Sometimes they leave town for the weekend with both ripping the whole time. I'm a landlord. This is the sort of crap I have to put up with my tenants doing.

[mousquet]

Originally Posted by jmecklenborg

Breaking news: it's cooler in the woods during the summer than outside the woods.

The issue is not as trivial as you seem to mean it in a dense urban environment.
I'll show you, cause studies by urban planners are spectacular in that matter.

• Video Link

The guy with glasses in that report from July of 2022 is a teacher in urban planning and an activist to defend trees in Central Paris.

0:45 Right there, you're standing on place de l'Opéra, a square usually full of tourists.
But there was none when they shot that report, because we were on a hellish heatwave.
That square is only limestone of buildings around and asphalt on the ground. Not a single tree on the square.
So it's what they call "îlot de chaleur" (a heat spot) in case of heatwave. The activist calls it a hostile environment, while it's a prime location at the center of the CBD in the inner city.

Temperature at ground level would be greater than in the Sahara desert when Paris is hit by some heatwave.

1:55 55.9°C, or 132.6°F on that very spot in front of the old opera house.
It goes up to 57 or 58°C (134 to 136°F)

Now look at that...

2:40 The guy just only walked over 100m (100 yards) to boulevard des Capucines. There are trees on the sidewalk right there, then the temperature drops to 23.7°C (74.7°F).
It is so unreal that I still wonder whether his gear would be reliable. I mean the difference over 100m is so insane that it seems fake.
Still, I don't think the guy would lie. That would be too bad for his reputation as a teacher in a college.

4:15 This woman is a researcher who works on very local weather conditions. She says they were working on a French-Indian satellite to spot "îlots de chaleur" more accurately, to the scale of a single urban block, like it couldn't get any more accurate.

This is obviously highly strategic in this city today.

[ocman]

Originally Posted by jmecklenborg

Breaking news: it's cooler in the woods during the summer than outside the woods.

We thought covering the whole place in concrete would do the job. We were doing it wrong all along.

[hauntedheadnc]

Originally Posted by ocman

We thought covering the whole place in concrete would do the job. We were doing it wrong all along.

Well, surely you must agree with him though that trees are so... plebian, so... vulgar, as the poors can enjoy them without paying, and rather than take action about overheating in cities on any macro level, the more effective strategy will be to lecture, for example, the Parisians about their hydration choices.

[edale]

Of course trees provide shade and cool the urban environment, but I struggle a bit with desires to have extensive tree cover in climates that don't naturally support forests. I see this in the Los Angeles area all the time, where neighborhood groups and tree enthusiasts are always advocating for more and more trees to be planted in public right of ways, trees retained on private property, etc. Historically, Los Angeles was not a tree covered place (in the mountains and along natural waterways, yes, otherwise, no), and we don't get the year round water required to keep trees healthy throughout the year. Yet that doesn't stop people from wanting their neighborhoods to look like Atlanta.

You move to a place because it's warm and sunny 9 months a year, but you also want a lush, shady, forested environment? For some reason, this just really bothers me. Don't move to a semi-arid climate and expect to live in a shady forest. In drier climates, I think cities should try to promote shade structures, awnings, colonnades, etc. rather than create artificial forests that require irrigation.

[Yuri]

Originally Posted by edale

Of course trees provide shade and cool the urban environment, but I struggle a bit with desires to have extensive tree cover in climates that don't naturally support forests. I see this in the Los Angeles area all the time, where neighborhood groups and tree enthusiasts are always advocating for more and more trees to be planted in public right of ways, trees retained on private property, etc. Historically, Los Angeles was not a tree covered place (in the mountains and along natural waterways, yes, otherwise, no), and we don't get the year round water required to keep trees healthy throughout the year. Yet that doesn't stop people from wanting their neighborhoods to look like Atlanta.

You move to a place because it's warm and sunny 9 months a year, but you also want a lush, shady, forested environment? For some reason, this just really bothers me. Don't move to a semi-arid climate and expect to live in a shady forest. In drier climates, I think cities should try to promote shade structures, awnings, colonnades, etc. rather than create artificial forests that require irrigation.

I like this concept of turning an arid area into forest. Like Johannesburg, located on a dry savannah and looks like Atlanta from above, full of trees imported from Brazilian Atlantic Rainforest.

In any case, the city itself changes way more the natural environment than the trees that come along as consequence.

[iheartthed]

Originally Posted by edale

Of course trees provide shade and cool the urban environment, but I struggle a bit with desires to have extensive tree cover in climates that don't naturally support forests. I see this in the Los Angeles area all the time, where neighborhood groups and tree enthusiasts are always advocating for more and more trees to be planted in public right of ways, trees retained on private property, etc. Historically, Los Angeles was not a tree covered place (in the mountains and along natural waterways, yes, otherwise, no), and we don't get the year round water required to keep trees healthy throughout the year. Yet that doesn't stop people from wanting their neighborhoods to look like Atlanta.

You move to a place because it's warm and sunny 9 months a year, but you also want a lush, shady, forested environment? For some reason, this just really bothers me. Don't move to a semi-arid climate and expect to live in a shady forest. In drier climates, I think cities should try to promote shade structures, awnings, colonnades, etc. rather than create artificial forests that require irrigation.

Maybe places in Southern California should implement sun shades, which are pretty common in southern Spain:



https://www.themayor.eu/en/a/view/se...n-summer-10149

Originally Posted by Yuri

I like this concept of turning an arid area into forest. Like Johannesburg, located on a dry savannah and looks like Atlanta from above, full of trees imported from Brazilian Atlantic Rainforest.

In any case, the city itself changes way more the natural environment than the trees that come along as consequence.

It would be extremely wasteful to plant a forest in a place like Los Angeles, which doesn't get enough rain to support that type of environment.

[Yuri]

Originally Posted by iheartthed

It would be extremely wasteful to plant a forest in a place like Los Angeles, which doesn't get enough rain to support that type of environment.

I'm not advocating for people actively doing that, specially in our days. However, in places that already happened, like Johannesburg and even Los Angeles to some extent, it's done. Better to have this coverage than decrease the green areas.

[JManc]

Originally Posted by Yuri

I'm not advocating for people actively doing that, specially in our days. However, in places that already happened, like Johannesburg and even Los Angeles to some extent, it's done. Better to have this coverage than decrease the green areas.

It's not a 'one and done' thing though, those trees in LA and Johannesburg require constant watering.

[iheartthed]

Originally Posted by Yuri

I'm not advocating for people actively doing that, specially in our days. However, in places that already happened, like Johannesburg and even Los Angeles to some extent, it's done. Better to have this coverage than decrease the green areas.

And it's not necessarily a coincidence that both of those regions are going through water crises.

[isaidso]

Originally Posted by iheartthed

It would be extremely wasteful to plant a forest in a place like Los Angeles, which doesn't get enough rain to support that type of environment.

I doubt they'd be so foolish as to plant species that aren't suited to their climate. They would surely consult with professionals that specialize in urban forestry and climate mitigation. You want trees/plants that flourish without human intervention. Many of those species don't provide as much shade as an oak tree would but there are many benefits beyond shade.