There is a place in So Cal now called The Aspens South Coast we lived in 30 years ago. It has (had?) an incredibly dense concentration of trees, something I’ve not seen since in that region, which is of course desert.
This time of year when you opened the gate that separated the treed interior from the parking lot you felt like the air conditioning had been turned on. We have very fond memories of the place. Its only disadvantage for me was that spring caused my allergies to go crazy.
I was in a heat wave in Andalusia region in Spain and was visiting Medieval Arabic monuments and gardens. They have very interesting designs in terms of shapes, plant and tree selections and wall placements that produced very noticeable temperature differences. To say nothing of the scent of the lemon trees.
Genuine question for people in the field. My understanding is that the cooling effect of trees is primarily driven by evaporative cooling. That is, the shade effect only really exists because the plant does not shrivel up and die due to storing water. How much more effective are trees vs. big swamp coolers? Even in this article, they admit that daytime cooling of half a degree requires 3 times more water.
There is something to be said for the parts about shading the surface too though. You're unlikely to cool an entire desert a significant amount with water you bring in but if that's something that happens as part of keeping the actual surfaces in the city cooler during peak heat times on top of the air cooling effects of evaporation then the sum result is greater than the parts in terms of effect.
Of course it's Vegas, I wouldn't be surprised if we decided to make the downtown completely indoors so we could just run AC in the streets too. It's not exactly the city of practicality.
during the day, trees provide significant shade by intercepting solar radiation, reducing mean radiant temperature (up to 16 °C)
Sadly they work the opposite way at night, they don't allow SPACE to cool the ground. A textil/plastic plate moved automatically can provide more cold, if that's the goal.
It really depends on how broad and high the tree canopy is; you don’t need super high tree density to provide a lot of shade.
The main benefit over other solutions is that properly selected trees require very little upkeep from humans, unlike anything mechanical or requiring movement. Though I imagine that is less the case in Vegas.
>> the downtown completely indoors so we could just run AC in the streets too.
So ... a shopping mall? Many cities do this already, linking various public indoor spaces by walkways/tunnels. Also those cities where the air outside is too cold. A few canadian universities link buildings with tunnels so students can avoid going outside.
Trees excel at harvesting water. When you water a tree, there is evaporative cooling like an artificial cooler but during the night, the dew falls back on the leaves and the ground where some of it finds its way back to the trees (possibly via an invertebrate first). Also the reflectiveness of leaves helps. Then there's the soil where layers of dead leaves, wood and others accumulate, sequester CO2 and create a sponge. Finally, by virtue of making the region cooler, rain is more likely to fall. Humans can probably engineer something better but the bar is high.
Right, but as pointed out in TFA & below the cooling from evaporation is almost negligible compared to that from the shade. Maybe Vegas would be okay with conserving their water too
For reader clarification: accumulating carbon in soil from decaying plant matter still leaves it part of short term carbon cycling, not to be confused with geological-time carbon sequestration. As you know.
Not that simple. When carbon in the soil rises beyond a certain percentage (a tree falls) it'll convert back to CO2 because of the bugs eating it. But if the percentage starts at zero (in a desert) and an ecosystem settles there, the percentage will rise and stay above zero for as long as the ecosystem survives. Basically the plants generate matter as fast as wildlife eats it.
This sequestration can be long term if things go well or it can be short term if plants die in large numbers (because of climate change, diseases...).
Yes, and cities with lots of trees are way more livable due to this. Planners in our town seem to hate trees with a passion, thank god we‘re moving away from this concrete desert.
Trees in cities are expensive to maintain, which is why they're often on the chopping block when budgets get tight. This is especially true in places like Las Vegas where there is little natural tree cover due to the climate. You have to have a staff of arborists to keep the trees alive in such a harsh environment.
Indeed, the town I‘m living in was 80% destroyed during WWII and that still shows in its finances. It’s amazing how long major disaster affects a region. Big drug issues, highest cancer rate in the country etc
The problem is that to get these effects you need large canopies of trees, and to get that to happen the trees have to take the space of something else. For street trees it takes away land from parking or traffic lanes; for properties it occupies both horizontal and vertical square footage since the sky above the tree needs to be clear. These are unpopular with some political affiliations and interest groups.
Even without any evaporative effect, the air cooling of leaves (at least bringing them to the surrounding air temperature) happens more easily than that of concrete pavement due to height and larger surface area. The concrete can easily get heated much hotter than the air at even 10-20ft.
Wrt. water consumption - Mediterranean species like say olive trees are kind of optimized for low water consumption, by for example having leaves covered with wax-like stuff decreasing evaporation.
Trees are also vertical structures. Any vertical structure will absorb some of the light, turning it into heat, then be cooled by rising air. This keeps the heat from getting to the ground, with or without evaporation. In other words, instead of the sidewalk getting hot, something 20+ feet in the air get hot. Hot air rises and the air near the ground stays cooler.
The increased water usage is tough because we're serious about water reclamation here in Vegas, but you can't reclaim water lost to evaporation, which is why there are policies (and serious fines) around excessive landscape watering. It might not be a worthwhile tradeoff, especially if there are alternate cooling methods that don't involve water loss.
Trees are great, but ultimately a pretty ridiculous idea if the goal is to create shade, even if you're not worried about water consumption. Avoiding concrete walls or overhangs is smart because you don't want the thermal mass.. but of course you can build these things out of fabric or thin metal.
The funny thing is, if you build a wall or canopy to avoid the water consumption plus literally waiting a decade for a tree to get tall.. now you're probably in violation of your HOA height restrictions, etc. Desert cities need to basically drop the idea of conforming to the typical expectations of visitors and newcomers by trying to add greenery. It's better to add shade, dig underground, build wind-catchers[1], salsabils[2]. There's tons of basic things like making sure roof surfaces are more reflective, and more strategic architectural things[3] that can be done to improve things and the techniques have been used forever
You know how a lot of classic midcentury modern houses (which you can still find in downtown Vegas!) have those kind of lattice-y decorative walls and panels? Are those actually functional for reducing heat and not just cool-looking?
part of the cooling effect that trees produce is from photosynthesis, the percentage of light converted to plant matter can be as high as 1.5%
more will be reflected, and the shaded area will of course,be shaded, and then there is transpiration of water, which varys greatly with species.other effects will be due to the built environment, where a lot of asphalt and concrete could mostly obliterate the real effects of a few trees.
from wiki "The average rate of energy captured by global photosynthesis is approximately 130 terawatts, which is about eight times the total power consumption of human civilization"
The point of that article is that in many places the evaporative cooling is the main thing but in Vegas the water situation is such that it's more about the shade so the optimal tree is something that gives shade but doesn't need a lot of water.
Right where I am sitting now I have an LED strip above my desk and when I have my shirt off (right now) I can very definitely feel the radiant energy when it is on, so if it is really hot I either turn it off or switch it to green because the eye is most sensitive to green light. In fact, as I'm writing this, I just set the backlight on the 55-inch TV I use as a computer monitor down so I'd feel more comfortable.
"Water harvesting" has been around for a long time. I think I first saw a water harvesting device in the U.S. Army Survival manual in the 1980s. It's an active research area and devices continue to improve.
I wasn't trying to be condescending, just trying to point out that trees might not be the most viable structure. Last time I was in southern Arizona when I wanted some relief I'd just find a solar panel installation in a parking lot and hang out under that.
Trees acts for their little thermal mass and large surface exposed to air, essentially IR radiation from the Sun can't much reach the ground or humans under trees (if they are large and dense enough) and the part of the radiation touching trees get quickly dispersed in the air (climbing the atmosphere).
The limited effect is that cities are dense and can't be made as forest so trees can't do nothing for buildings taller them them.
I recently bought some wooded land and unlike most people I know I've been extremely selective cutting down trees on it.
It's actually comfortable to be outside there. Even in the summer it's almost completely shaded. I was kind of surprised how extreme it is. I know trees make it harder to work and if you're hiring people they probably can't tolerate it but since I'm doing everything myself I don't have to clear everything and wait for it to grow back.
I think they all have something they want to do with it and just don't see how to accomplish that with the trees there. I know some people just don't like how trees feel (my mom is like this for example, something about growing up in the midwest I guess) but I think for most people it's just because hired labor and machinery can't fit between them.
I don’t think planting trees is only for cooling things down. Sometimes it’s just about helping people feel like they can go outside. In really hot places, even a bit of shade can change your mind about stepping out.
I'm sure any future endeavor to plant trees in the goddamn desert will have no negative environmental consequences at all. It's not as if the city in the goddamn desert is already in the middle of a regional water crisis as of last year or anything...
> In 2014, Southern Nevada’s gross water demand was about 205 gallons per capita per day (GPCD). In the region, single- and multi-family households account for 60 percent of water consumption—70 percent of which is used for landscaping.
That's because that doc is talking about Southern Nevada (read: Vegas) in isolation, 78% of Nevada water usage is agriculture (followed by 13% residential, 7% mining)
This is relevant though towards the argument that Vegas isn't typical in it's water consumption and trees may well have a much more detrimental effect than in other places.
Having lived in the desert, and not talking Vegas, but Nevada desert where folks bought cheap lots, dragged a single or double wide trailer into it, and started a life.
Trees were the first thing planted. Fast growing trees, placed to cast shade on the house.
After a few years, those dirt lots transformed into some very nice properties where sitting outside in the shade with the desert zephyrs rustling the leaves provide a very nice, idyllic place for conservation or reading.
There are a few of these plots outside of Crestone, CO that I've always dreamed of visiting. They truly look like oases and it must be surreal to sit in the shade and read while looking out onto the surrounding desert.
Southern Nevada uses a tiny amount of water compared to most states, about 2% of the total that’s apportioned from the CO river, and recycles about 40% of it. For indoor usage, 99% of water is recycled.
I agree growing things in the desert may be inefficient, but speaking for the CO river, that problem is in California and Arizona.
> [Las Vegas] used 38 billion gallons less water in 2024 than in 2002, despite a population increase of approximately 829,000 residents during that time. This represents a 55 percent decline in the community’s per capita water use since 2002.
Is it your suggestion that the Levant was once as well-watered and verdant as, say, the Netherlands or Hawaii?
While human activities undoubtedly contributed to desertification, the Levant is geographically and climactically a desert. The amount of surface water that is available may be directly influenced by human behavior, but I do not think that human behavior changed the fundamentals of the landscape.
We identified why north Africa greened approximately every 21,000 years over the past eight million years. It was caused by changes in the Earth’s orbital precession - the slight wobbling of the planet while rotating. This moves the Northern Hemisphere closer to the sun during the summer months.
*What Really Turned the Sahara Desert From a Green Oasis Into a Wasteland?* - 10,000 years ago, this iconic desert was unrecognizable. A new hypothesis suggests that humans may have tipped the balance
While I personally veer toward the more recent slight orbital variation cause, neither account factors much in the current AGW debate .. cyclic changes in local regions of the planet are a distinct issue from a steady rise in global atmospheric insulation properties.
The Sahara was once a forest. Its desertification was not caused by human activity.
On the other hand for the Fertile Crescent: the overuse of irrigation and water steering with shorter term agricultural goals with only direct affects in mind. The area was largely marshlands in the past.
And also mismanagement of forests lead to desertification of formerly fertile areas on the timescale before the current large scale climate change era began. This was before humanity could have as big possible part in the forming of climate as currently.
Yes, because living in the desert is absurd and obviously unnatural. Setting aside of course 3,000 years of civilization in Egypt. While we're at it, let's also unpack all these skyscrapers in New York and Tokyo and make sure no one is living at any height greater than the monkeys in the trees.
Egypt went from 8 million to 80 million in the last century. In large part because of the rest of the world (massive grain imports from Ukraine ... for example). But it can obviously work, thanks to globalization and how cheap it's to transport things by container ships.
Desalination that runs off of Solar panels makes it pretty viable for places like Dubai to exist. The cheap solar energy from the Desert, makes it attractive for future data centers to be placed there. Also, Ancient Egypt had slaves. A lot of the modern middle eastern states rely on cheap labour from India and Afghanistan.
And Oil money ...
My understanding is that agriculture in the desert works because of all the sunlight, so if water is provided it ends up actually being really good for growing plants.
(also, I don't think the Central Valley is actually a desert?)
Similarly, agriculture in a swamp works because of all the water. So if soil and sunlight is provided it ends up actually being really good for growing plants.
When I think of swampy areas I'm familiar with, they don't get as much sunlight as desert areas. It's possible to provide water to many areas that don't have a lot, but increasing total sunlight hours isn't possible.
Sure you can, you just give them unlimited free electricity and shine light on them. Basically what we do with water to sustain agriculture in deserts.
There may be counter intuitive effects in there. Plants roots creates water buffer zone underground that can capture some of rainfall and make better use of it, allowing larger growth.
MIT should deploy their desert water tech in LV[0]
Since the point of the trees has been discovered to be just shade and not evaporative cooling, they just need to figure a way to reorient their panels?
Perhaps the desert will repent its desertness and accept that sand, minimal water and a massive diurnal temperature range will somehow become amical towards good old Plane trees.
OK, let's go full mad world: a vast web of PV for power. Is there a handy massive water resource deep underground? If not then moisture in the air will need redeploying. Tall towers and probably gobs of power are indicated for that.
Trees grow in the desert. Mesquites, pines, junipers and more are all widespread in areas around Vegas. You don't need a tropical paradise to have vegetation, as the native forests of Arizona and Utah show.
There are proven methods for growing plants and trees in arid regions [0], but they have disadvantages which will become more evident as desertification expands with global warming. I agree that forcing non-native trees there is a losing battle in the long run.
If people were really serious about living in deserts in a sustainable way, they can't expect to have decorative greenery or classic architecture. A society as advanced as ours should be able to make compromises that allow modern comforts while adapting so well to their environment that the cities would look almost alien.
Not alien. Arabic, Spanish, mid-mediterranean, Puebloan, and a few more.
The architecture has existed for centuries, maybe even millenia. Some of us already live that way.
The irony is that the key thing - large thermal mass - has now become the province of only those with lots of money, or those with no money. Everyone in the middle is stuck with silly construction options for a desert climate.
No. Different types of trees provide different amounts of cover and different types of trees thrive in different climates. Las Vegas does have a particular climate that will make supporting some trees not worth the effort. Vegas also has a particular layout where most of the pedestrians are expected to be.
I've only scanned the abstract but the conclusion seems too weak given the other stated findings. Sure given different metrics (air temp vs radiant heat) may give different stories for different trees, but that wouldn't lead me to conclude it needs to be evaluated on a "case by case basis" more so than the metric depends. That is not the same thing as "case by case basis."
They should be more proud of their findings. Why insult it out of the gate?
I saw video last week in India there was similar experiment done in sun the temperature 45 degrees C and 30 step walk under the tree the temperature 36 degrees C. We need more trees as an easy solution
I hope there would be enforced regulation around this kind of thing in cities in India. In residential areas, it's common that your house takes up almost all of your available plot space, and on top of that mostly constructed from concrete.
Air temperature is already high (e.g. 36C at my location just now), and radiant heat from sun and concrete can make the felt temperature more like 60C.
It's sad that new real-estate layouts continue to be approved, which will only be good for this type of dense concrete hell.
> The selected tree species is Bur Oak, given that it is included in the SNWA Regional Plant (SNWA 2021) list, it is marked as a street tree in the list...
Who the hell is planting oaks in Vegas? Oaks are non native and moderately water intensive trees. If this study is based on oaks, it calls into question the validity of the data since this is a tree that absolutely does not belong in the Mojave desert.
Las Vegas averages ~4 inches of rain (a little more than 10 cms) per year with less than 2 days of precipitation per month, mostly in very short intense bursts. In June and July, when a tree needs it most because of the ever intensifying heat waves, the rains may not happen at all. Even the desert trees struggle in such an inhospitable environment and can be drought deciduous to conserve water (a notable desert adaptation among many). Without tons of water, an oak doesn't stand a chance.
The best way to produce shade in the Nevada desert is with solar panels.
The sky is rarely cloudy and solar just blasts all day every day here.
I covered my backyard in Vegas with ground panels and now I charge my EV off of a 100% off grid solar system. The sun provides enough energy in my small yard for 2-3x my driving needs.
Solar panels can be engineered to also optimize cooling, by selectively increasing their reflectivity at wavelengths that are neither useful for electricity production nor for radiation of their waste thermal energy.
"[...] we design a photonic cooler made of one-
dimensional photonic films that can strongly radiate heat
through its thermal emission while also significantly reflecting
the solar spectrum in the sub-band-gap and ultraviolet regimes.
We show that applying this photonic cooler to a solar panel can lower the cell temperature by over 5.7 °C."
I've just been presented with a captcha thingie asking me to select all things that can be picked up by a pair of chopsticks described as "the tool in the image"
Fuck off.
Then that vanished and another even more vapid effort appeared.
Fuck off.
If you need to piss around with this sort of nonsense, you probably shouldn't be entrusted with a website.
Looping redirects on archive.XX urls often traces back to the use of Cloudflare DNS resolver .. the archive folk have some beef with Cloudflare over (?) handling privacy (?) and loop redirects on connections that arrive via that path.
It's a new captcha type for myself also. Interesting as it requires spatial reasoning and a bridge of understanding between text request and objects in images - although it falls to the usual farm of human captcha solvers.
nice, well i am using quad9; archive.org had 503's too (edit: lol i wonder if it did complete for me but somehow something else caused a loop - i never went to the search prompt afterward)
Is it just me, or has anyone also noticed that trees in southern climates closer to the equator (not jungles) have very few leaves and shade as opposed to trees in climates away from the equator (not tundras)?
What happens if you import northern US trees, the ones that produce a lot of shade, into southern states? Has this been tried?
It is also why there is very little shade in, say, Florida. Only occasional parts of the Martin Grade “scenic” highway look like a regular scene in the north.
The short answer is, they would die. The trees are the way they are because they've adapted to their environment. At a high level, trees in hot sunny areas will have smaller leaves because they can get enough sunlight from a smaller surface area, and smaller leaves lose less water.
But it is more complicated than that, of course. It's not just "how hot does it get", but also how much water is available, how windy it is, how cold it gets, and a million other environmental factors. That's why there is such a wide variety among the plants on earth.
(and yes, it has been tried. Check out the youtube channel "crime pays but botany doesn't")
Florida has plenty of shade, though you wouldn't know it considering our city planning. Anything that isn't too dense for humans is pure urban hellscape.
But lack of water will become a huge problem when your city is growing that fast in a heating climate.
Edit: And cooling only works inside buildings or cars. Part of a comfortable city is being able to go outside and have a social life outside of a casino.
Municipal uses like drinking, showering, and watering ornamental plants is a tiny pct of desert water use. Most of it is crop irrigation, because if you can will water into existence then crops grow great in sunny deserts.
If the US' alfalfa exports to Saudi Arabia went down by 10%, we would never have a municipal water shortage in the American West in the next century.
Lack of water is a political problem. We have vast oceans which can be desalinated. Israel gets 85% of its water from desalination, they have gone from water shortages to having a water surplus.
We pump oil via pipelines vast distances, we can do the same with water.
We have virtually unlimited energy locked in Uranium which could power desalination plants, or heck you could power them with solar.
There’s plenty of water for the whole planet. There’s also plenty of clean energy (see nuclear and solar point earlier). But tapping these resources requires a functional government or at least a bureaucracy willing to allow companies to build.
There are people pushing for more shade in cities as an adaptation for a warming world. There is some crossover with the push for a reduction in cars and generally reducing the footprint of streets. Looking at old cities in hot climates I can see how this could make sense.
For Las Vegas, Cottonwoods are native and grow pretty quickly. Like many poplars they were used to grow shelterbelts.
That's a great idea, but hard for the city of Las Vegas to implement. Clark County doesn't have any ability to build a city not in a desert either. The state of Nevada doesn't have much of anywhere to put a non-desert city either.
Very few municipalities are willing to deny new residents, either. It wouldn't be anywhere on my list of viable places to live, but population growth in the Las Vegas metro area has been consistently large since 1910 until recently (only 10% growth from 2010 to 2020). The municipalities should likely invest in livability and comfort where possible.
There is a place in So Cal now called The Aspens South Coast we lived in 30 years ago. It has (had?) an incredibly dense concentration of trees, something I’ve not seen since in that region, which is of course desert.
This time of year when you opened the gate that separated the treed interior from the parking lot you felt like the air conditioning had been turned on. We have very fond memories of the place. Its only disadvantage for me was that spring caused my allergies to go crazy.
Totally worth it.
I was in a heat wave in Andalusia region in Spain and was visiting Medieval Arabic monuments and gardens. They have very interesting designs in terms of shapes, plant and tree selections and wall placements that produced very noticeable temperature differences. To say nothing of the scent of the lemon trees.
This? https://maps.app.goo.gl/f1q3wMkoagx2aWtC6
I see some trees but it doesn't seem like a dense concentration.
Genuine question for people in the field. My understanding is that the cooling effect of trees is primarily driven by evaporative cooling. That is, the shade effect only really exists because the plant does not shrivel up and die due to storing water. How much more effective are trees vs. big swamp coolers? Even in this article, they admit that daytime cooling of half a degree requires 3 times more water.
There is something to be said for the parts about shading the surface too though. You're unlikely to cool an entire desert a significant amount with water you bring in but if that's something that happens as part of keeping the actual surfaces in the city cooler during peak heat times on top of the air cooling effects of evaporation then the sum result is greater than the parts in terms of effect.
Of course it's Vegas, I wouldn't be surprised if we decided to make the downtown completely indoors so we could just run AC in the streets too. It's not exactly the city of practicality.
>on top of the air cooling effects of evaporation
I think you meant to say *on top of shade* because blocking the sun is the main effect here (the geometry makes more sense too!)
Less confusing phrase from abstract which implies that the 0.5deg evaporative cooling is almost a rounding error:
It really depends on how broad and high the tree canopy is; you don’t need super high tree density to provide a lot of shade.
The main benefit over other solutions is that properly selected trees require very little upkeep from humans, unlike anything mechanical or requiring movement. Though I imagine that is less the case in Vegas.
To me what seems too good to be possible is the triple combo of shade, radiative cooling, and water harvesting
Only ambient sunlight needed here, but they'd have to make the panels horizontal (indeed, curtained at night like you say) somehow:
https://www.thebrighterside.news/post/mits-high-tech-hydroge...
Edit I guess the low-maintenance option might be some kind of giant variegated Madagascan succulent
>> the downtown completely indoors so we could just run AC in the streets too.
So ... a shopping mall? Many cities do this already, linking various public indoor spaces by walkways/tunnels. Also those cities where the air outside is too cold. A few canadian universities link buildings with tunnels so students can avoid going outside.
Also: Toronto's PATH - https://www.toronto.ca/explore-enjoy/visitor-toronto/path-to...
Cooling the streets is nothing like a mall or growing tbe walkway connections, those are much too sensible.
If you cover the roof in solar, it will generate more than sufficient power to air condition it.
They do outdoor AC in [some places in some] parks in Qatar.
Sounds like Qatar. Innovative and expensive.
Qatar is basically Vegas if it had more money.
Under the sand on the beach, too!
Trees excel at harvesting water. When you water a tree, there is evaporative cooling like an artificial cooler but during the night, the dew falls back on the leaves and the ground where some of it finds its way back to the trees (possibly via an invertebrate first). Also the reflectiveness of leaves helps. Then there's the soil where layers of dead leaves, wood and others accumulate, sequester CO2 and create a sponge. Finally, by virtue of making the region cooler, rain is more likely to fall. Humans can probably engineer something better but the bar is high.
>Trees excel at harvesting water.
Specifically, some kind of giant succulent would be best for arid climes
https://en.wikipedia.org/wiki/Aloidendron_dichotomum
But they probably don't evaporate water and cool as much as other plants and trees.
Right, but as pointed out in TFA & below the cooling from evaporation is almost negligible compared to that from the shade. Maybe Vegas would be okay with conserving their water too
It's counterintuitive..
For reader clarification: accumulating carbon in soil from decaying plant matter still leaves it part of short term carbon cycling, not to be confused with geological-time carbon sequestration. As you know.
Not that simple. When carbon in the soil rises beyond a certain percentage (a tree falls) it'll convert back to CO2 because of the bugs eating it. But if the percentage starts at zero (in a desert) and an ecosystem settles there, the percentage will rise and stay above zero for as long as the ecosystem survives. Basically the plants generate matter as fast as wildlife eats it.
This sequestration can be long term if things go well or it can be short term if plants die in large numbers (because of climate change, diseases...).
In the abstract it discusses that most of the effect (16deg Celsius) is from reduced radiative heating and only a few degrees from evaporation.
Mostly the benefit is instead of having the concrete under you absorb and emit the sun, the leaves above you do.
This dramatically reduces the heat we feel at human height.
> the effect (16deg Celsius)
Did I read that right? 16°C seems like an enormous effect.
Seems like trees would be a small investment to effectively get "outdoor AC-ish"?
EDIT: for those of us who are more comfortable with Freedom Units, that's like going from 104°F to 75°F!
Yes, and cities with lots of trees are way more livable due to this. Planners in our town seem to hate trees with a passion, thank god we‘re moving away from this concrete desert.
Trees in cities are expensive to maintain, which is why they're often on the chopping block when budgets get tight. This is especially true in places like Las Vegas where there is little natural tree cover due to the climate. You have to have a staff of arborists to keep the trees alive in such a harsh environment.
Indeed, the town I‘m living in was 80% destroyed during WWII and that still shows in its finances. It’s amazing how long major disaster affects a region. Big drug issues, highest cancer rate in the country etc
The problem is that to get these effects you need large canopies of trees, and to get that to happen the trees have to take the space of something else. For street trees it takes away land from parking or traffic lanes; for properties it occupies both horizontal and vertical square footage since the sky above the tree needs to be clear. These are unpopular with some political affiliations and interest groups.
Replacing inefficient street parking and wide roads with trees is a straightforward win.
It is like Sim City 1 where crossroads generated traffic, so you'd replace them with parks.
Obligatory response to 'Freedom Units' for those who haven't seen it: https://www.youtube.com/watch?v=JYqfVE-fykk
Even without any evaporative effect, the air cooling of leaves (at least bringing them to the surrounding air temperature) happens more easily than that of concrete pavement due to height and larger surface area. The concrete can easily get heated much hotter than the air at even 10-20ft.
Wrt. water consumption - Mediterranean species like say olive trees are kind of optimized for low water consumption, by for example having leaves covered with wax-like stuff decreasing evaporation.
MIT should deploy their desert water harvesting tech in LV[0]
they just need to figure a way to reorient their panels to provide shade?
[0] only sunlight needed
https://www.thebrighterside.news/post/mits-high-tech-hydroge...
Re: olives, hopefully the terpenes can also help cloud formation
Trees are also vertical structures. Any vertical structure will absorb some of the light, turning it into heat, then be cooled by rising air. This keeps the heat from getting to the ground, with or without evaporation. In other words, instead of the sidewalk getting hot, something 20+ feet in the air get hot. Hot air rises and the air near the ground stays cooler.
The increased water usage is tough because we're serious about water reclamation here in Vegas, but you can't reclaim water lost to evaporation, which is why there are policies (and serious fines) around excessive landscape watering. It might not be a worthwhile tradeoff, especially if there are alternate cooling methods that don't involve water loss.
Trees are great, but ultimately a pretty ridiculous idea if the goal is to create shade, even if you're not worried about water consumption. Avoiding concrete walls or overhangs is smart because you don't want the thermal mass.. but of course you can build these things out of fabric or thin metal.
The funny thing is, if you build a wall or canopy to avoid the water consumption plus literally waiting a decade for a tree to get tall.. now you're probably in violation of your HOA height restrictions, etc. Desert cities need to basically drop the idea of conforming to the typical expectations of visitors and newcomers by trying to add greenery. It's better to add shade, dig underground, build wind-catchers[1], salsabils[2]. There's tons of basic things like making sure roof surfaces are more reflective, and more strategic architectural things[3] that can be done to improve things and the techniques have been used forever
[1] https://en.wikipedia.org/wiki/Windcatcher [2] https://en.wikipedia.org/wiki/Salsabil_(fountain) [3] https://en.wikipedia.org/wiki/Passive_cooling
You know how a lot of classic midcentury modern houses (which you can still find in downtown Vegas!) have those kind of lattice-y decorative walls and panels? Are those actually functional for reducing heat and not just cool-looking?
How to Dress and Undress your Home | LOW←TECH MAGAZINE
https://solar.lowtechmagazine.com/2025/06/dressing-and-undre...
The perforated architectural elements designed to filter sunlight are referred to as brise-soleil (sun-breaker in french)
https://en.wikipedia.org/wiki/Brise_soleil
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It's confusing phrasing.
Increasing *evaporative* cooling by 0.5deg requires 3x more water, but shade alone is the *main* mechanism,it doesn't require water.
>during the day, trees provide significant shade by intercepting solar radiation, reducing mean radiant temperature (up to 16 °C)
part of the cooling effect that trees produce is from photosynthesis, the percentage of light converted to plant matter can be as high as 1.5% more will be reflected, and the shaded area will of course,be shaded, and then there is transpiration of water, which varys greatly with species.other effects will be due to the built environment, where a lot of asphalt and concrete could mostly obliterate the real effects of a few trees. from wiki "The average rate of energy captured by global photosynthesis is approximately 130 terawatts, which is about eight times the total power consumption of human civilization"
https://en.wikipedia.org/wiki/Photosynthesis
The point of that article is that in many places the evaporative cooling is the main thing but in Vegas the water situation is such that it's more about the shade so the optimal tree is something that gives shade but doesn't need a lot of water.
Right where I am sitting now I have an LED strip above my desk and when I have my shirt off (right now) I can very definitely feel the radiant energy when it is on, so if it is really hot I either turn it off or switch it to green because the eye is most sensitive to green light. In fact, as I'm writing this, I just set the backlight on the 55-inch TV I use as a computer monitor down so I'd feel more comfortable.
So an umbrella?
Yeah, but like an umbrella made by something like Drexler's nanotechology.
How about something more ... Realistic
https://www.thebrighterside.news/post/mits-high-tech-hydroge...
That's the opposite of a tree, which turns drinking water into nothing
"Water harvesting" has been around for a long time. I think I first saw a water harvesting device in the U.S. Army Survival manual in the 1980s. It's an active research area and devices continue to improve.
Passive? Hydrophobic+Dessicant? dew collector? In the desert?
Dew collector seems to make the most sense for 1980
If we're being condescending: 'So, a parasol?'.
I wasn't trying to be condescending, just trying to point out that trees might not be the most viable structure. Last time I was in southern Arizona when I wanted some relief I'd just find a solar panel installation in a parking lot and hang out under that.
Swamp coolers can't generally provide shade.
I got a great business idea now.
Trees acts for their little thermal mass and large surface exposed to air, essentially IR radiation from the Sun can't much reach the ground or humans under trees (if they are large and dense enough) and the part of the radiation touching trees get quickly dispersed in the air (climbing the atmosphere).
The limited effect is that cities are dense and can't be made as forest so trees can't do nothing for buildings taller them them.
> trees can't do nothing for buildings taller them them.
Plant trees on top!
Still not useful: facades remain exposed and so the largest thermal mass of the building.
Some of it is converted to chemical energy used for the tree’s growth etc chatgpt says 30-40%
There is literally no difference. Water is water, and its specific heat of evaporation doesn't depend on the way it's evaporated.
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Related:
Las Vegas is embracing a simple climate solution: More trees (npr.org) 21 days ago | 143 comments https://news.ycombinator.com/item?id=44231151
Nights in Las Vegas Are Becoming Dangerously Hot (nytimes.com) 10 months ago | 1 comment https://news.ycombinator.com/item?id=41223831
I recently bought some wooded land and unlike most people I know I've been extremely selective cutting down trees on it.
It's actually comfortable to be outside there. Even in the summer it's almost completely shaded. I was kind of surprised how extreme it is. I know trees make it harder to work and if you're hiring people they probably can't tolerate it but since I'm doing everything myself I don't have to clear everything and wait for it to grow back.
I wish more land owners were as conscious as you. Most see the land as a piggy bank and trees are nuances and cost centres.
I think they all have something they want to do with it and just don't see how to accomplish that with the trees there. I know some people just don't like how trees feel (my mom is like this for example, something about growing up in the midwest I guess) but I think for most people it's just because hired labor and machinery can't fit between them.
I don’t think planting trees is only for cooling things down. Sometimes it’s just about helping people feel like they can go outside. In really hot places, even a bit of shade can change your mind about stepping out.
That captcha sure reduces the effectiveness of me reading that by 100%.
Why is Las Vegas, NV referred to as ‘Vegas’, but Los Angeles, CA is not referred to as ‘Angeles’?
Number of syllables.
"Angeles" has 3, and is already too much. So they say L.A. (2 syllables).
It's the same reason you call New York in full (not N.Y.), as it's already 2 syllables.
Because it starts with a consonant
It just seems unduly informal in the context of technical paper. Not sure why it bugged me..
edit: referencing the HN title, not the paper itself
I'm sure any future endeavor to plant trees in the goddamn desert will have no negative environmental consequences at all. It's not as if the city in the goddamn desert is already in the middle of a regional water crisis as of last year or anything...
https://www.knpr.org/show/knprs-state-of-nevada/2024-08-29/w...
Most places in the west, the water used for 'municipal' stuff is a small fraction of the total.
For instance where I live east of the Cascades, in the dry part of Oregon, only like 10% of the water used goes to the cities.
https://www.centraloregonlandwatch.org/update/2021/5/5/droug...
Street trees are hugely beneficial and if you want to cut something (ha ha), you want to look at things like lawns or golf courses.
In New Mexico and Arizona, 7% of water is for residential use, another 7% is for retail, commercial and power generation. 75% goes to agriculture.
Trees in cities are not about reducing water usage by any significant amount. They are still lovely, though.
> In 2014, Southern Nevada’s gross water demand was about 205 gallons per capita per day (GPCD). In the region, single- and multi-family households account for 60 percent of water consumption—70 percent of which is used for landscaping.
I found this quote in this 2016 PDF from the EPA:
https://www.epa.gov/sites/default/files/2017-02/documents/ws...
That's because that doc is talking about Southern Nevada (read: Vegas) in isolation, 78% of Nevada water usage is agriculture (followed by 13% residential, 7% mining)
https://extension.unr.edu/publication.aspx?PubID=4764
True, and also 75% of Nevada’s population is in the Las Vegas metro area.
You understand that factoid strengthens the point of the person you're replying to right
I am not attempting to strengthen or weaken anyone’s points. Not even regarding the definition of the word “factoid!”
This is relevant though towards the argument that Vegas isn't typical in it's water consumption and trees may well have a much more detrimental effect than in other places.
Having lived in the desert, and not talking Vegas, but Nevada desert where folks bought cheap lots, dragged a single or double wide trailer into it, and started a life.
Trees were the first thing planted. Fast growing trees, placed to cast shade on the house.
After a few years, those dirt lots transformed into some very nice properties where sitting outside in the shade with the desert zephyrs rustling the leaves provide a very nice, idyllic place for conservation or reading.
There are a few of these plots outside of Crestone, CO that I've always dreamed of visiting. They truly look like oases and it must be surreal to sit in the shade and read while looking out onto the surrounding desert.
Southern Nevada uses a tiny amount of water compared to most states, about 2% of the total that’s apportioned from the CO river, and recycles about 40% of it. For indoor usage, 99% of water is recycled.
I agree growing things in the desert may be inefficient, but speaking for the CO river, that problem is in California and Arizona.
https://www.snwa.com/water-resources/where-water-comes-from/...
https://lvgea.org/water/
Agriculture is the problem, not urban trees
Not people attempting to live in a desert?
Vegas is hardcore about not wasting water because the water we do capture gets treated and put back in Lake Mead :)
https://www.cleanwaterteam.com/about-us/who-we-are
> [Las Vegas] used 38 billion gallons less water in 2024 than in 2002, despite a population increase of approximately 829,000 residents during that time. This represents a 55 percent decline in the community’s per capita water use since 2002.
https://www.lvvwd.com/conservation/measures/index.html
The earliest human civilizations where all located in deserts. It is not a foreign thing to our species at all.
However, large scale commercial agriculture in desert areas without significant ground water - that's a new thing, and it's a problem.
Outside of greenhouses. It's only an issue in an open field. Once properly enclosed the high energy availability is a major upside.
Isn't it like the earliest (known) human civilization managed to create desert from their locations?*
(or were victims of non-anthropogenic desertification)
*note: the same process going on currently also via multiple means :(
Is it your suggestion that the Levant was once as well-watered and verdant as, say, the Netherlands or Hawaii?
While human activities undoubtedly contributed to desertification, the Levant is geographically and climactically a desert. The amount of surface water that is available may be directly influenced by human behavior, but I do not think that human behavior changed the fundamentals of the landscape.
Am I wrong?
Of interest:
(2023) - https://theconversation.com/the-sahara-desert-used-to-be-a-g... (2017) https://www.smithsonianmag.com/science-nature/what-really-tu...While I personally veer toward the more recent slight orbital variation cause, neither account factors much in the current AGW debate .. cyclic changes in local regions of the planet are a distinct issue from a steady rise in global atmospheric insulation properties.
The Sahara was once a forest. Its desertification was not caused by human activity.
On the other hand for the Fertile Crescent: the overuse of irrigation and water steering with shorter term agricultural goals with only direct affects in mind. The area was largely marshlands in the past.
And also mismanagement of forests lead to desertification of formerly fertile areas on the timescale before the current large scale climate change era began. This was before humanity could have as big possible part in the forming of climate as currently.
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Yes, because living in the desert is absurd and obviously unnatural. Setting aside of course 3,000 years of civilization in Egypt. While we're at it, let's also unpack all these skyscrapers in New York and Tokyo and make sure no one is living at any height greater than the monkeys in the trees.
Egypt went from 8 million to 80 million in the last century. In large part because of the rest of the world (massive grain imports from Ukraine ... for example). But it can obviously work, thanks to globalization and how cheap it's to transport things by container ships.
Desalination that runs off of Solar panels makes it pretty viable for places like Dubai to exist. The cheap solar energy from the Desert, makes it attractive for future data centers to be placed there. Also, Ancient Egypt had slaves. A lot of the modern middle eastern states rely on cheap labour from India and Afghanistan. And Oil money ...
The Nile is, uh, enormously relevant to Egyptian civilization.
Wait until you hear about the mighty Colorado. The Hoover dam wasn't just built to imprison Decepticons you know
What about the Decepticons he or she has yet to meet?
I think doing agriculture in a desert is more ridiculous than living there, but the Central Valley exists all the same.
My understanding is that agriculture in the desert works because of all the sunlight, so if water is provided it ends up actually being really good for growing plants.
(also, I don't think the Central Valley is actually a desert?)
Similarly, agriculture in a swamp works because of all the water. So if soil and sunlight is provided it ends up actually being really good for growing plants.
When I think of swampy areas I'm familiar with, they don't get as much sunlight as desert areas. It's possible to provide water to many areas that don't have a lot, but increasing total sunlight hours isn't possible.
Sure you can, you just give them unlimited free electricity and shine light on them. Basically what we do with water to sustain agriculture in deserts.
Much of it used to be a seasonal wetland/lake until the water was diverted into canals or pumped over the mountains.
>so if water is provided
^ the rub ^
It's not an either or type situation
No, but it is an 80-20 type situation. 80% of the water use is agricultural.
There may be counter intuitive effects in there. Plants roots creates water buffer zone underground that can capture some of rainfall and make better use of it, allowing larger growth.
MIT should deploy their desert water tech in LV[0]
Since the point of the trees has been discovered to be just shade and not evaporative cooling, they just need to figure a way to reorient their panels?
[0] only sunlight needed
https://www.thebrighterside.news/post/mits-high-tech-hydroge...
Perhaps the desert will repent its desertness and accept that sand, minimal water and a massive diurnal temperature range will somehow become amical towards good old Plane trees.
OK, let's go full mad world: a vast web of PV for power. Is there a handy massive water resource deep underground? If not then moisture in the air will need redeploying. Tall towers and probably gobs of power are indicated for that.
Trees grow in the desert. Mesquites, pines, junipers and more are all widespread in areas around Vegas. You don't need a tropical paradise to have vegetation, as the native forests of Arizona and Utah show.
> Is there a handy massive water resource deep underground
There was.
We've been sucking them dry for a century or more, everywhere they exist.
There are proven methods for growing plants and trees in arid regions [0], but they have disadvantages which will become more evident as desertification expands with global warming. I agree that forcing non-native trees there is a losing battle in the long run.
If people were really serious about living in deserts in a sustainable way, they can't expect to have decorative greenery or classic architecture. A society as advanced as ours should be able to make compromises that allow modern comforts while adapting so well to their environment that the cities would look almost alien.
0. https://en.wikipedia.org/wiki/Desert_greening
Not alien. Arabic, Spanish, mid-mediterranean, Puebloan, and a few more.
The architecture has existed for centuries, maybe even millenia. Some of us already live that way.
The irony is that the key thing - large thermal mass - has now become the province of only those with lots of money, or those with no money. Everyone in the middle is stuck with silly construction options for a desert climate.
This needing a study is like the discovery in Idiocracy that soil needs to be watered with water, not Brawndo's soft drink.
Plant trees, not ACs...
North America's greed for energy resources is just bonkers from an outside perspecive.
No. Different types of trees provide different amounts of cover and different types of trees thrive in different climates. Las Vegas does have a particular climate that will make supporting some trees not worth the effort. Vegas also has a particular layout where most of the pedestrians are expected to be.
The abstract does lay this out pretty well.
I've only scanned the abstract but the conclusion seems too weak given the other stated findings. Sure given different metrics (air temp vs radiant heat) may give different stories for different trees, but that wouldn't lead me to conclude it needs to be evaluated on a "case by case basis" more so than the metric depends. That is not the same thing as "case by case basis."
They should be more proud of their findings. Why insult it out of the gate?
I saw video last week in India there was similar experiment done in sun the temperature 45 degrees C and 30 step walk under the tree the temperature 36 degrees C. We need more trees as an easy solution
I hope there would be enforced regulation around this kind of thing in cities in India. In residential areas, it's common that your house takes up almost all of your available plot space, and on top of that mostly constructed from concrete.
Air temperature is already high (e.g. 36C at my location just now), and radiant heat from sun and concrete can make the felt temperature more like 60C.
It's sad that new real-estate layouts continue to be approved, which will only be good for this type of dense concrete hell.
> The selected tree species is Bur Oak, given that it is included in the SNWA Regional Plant (SNWA 2021) list, it is marked as a street tree in the list...
Who the hell is planting oaks in Vegas? Oaks are non native and moderately water intensive trees. If this study is based on oaks, it calls into question the validity of the data since this is a tree that absolutely does not belong in the Mojave desert.
oaks are at home in the Levante , syria, turkey Lebanon and spain - all partially desert places now, but oak foerested in the past.
Las Vegas averages ~4 inches of rain (a little more than 10 cms) per year with less than 2 days of precipitation per month, mostly in very short intense bursts. In June and July, when a tree needs it most because of the ever intensifying heat waves, the rains may not happen at all. Even the desert trees struggle in such an inhospitable environment and can be drought deciduous to conserve water (a notable desert adaptation among many). Without tons of water, an oak doesn't stand a chance.
This is a repeating study, seeing this again and again, so not sure about its novelty.
In Europe we even assigned our first "Chief Heat Officer", which makes total sense.
what does he do?
*She
I have no clue
I guess she is... hot
The best way to produce shade in the Nevada desert is with solar panels.
The sky is rarely cloudy and solar just blasts all day every day here.
I covered my backyard in Vegas with ground panels and now I charge my EV off of a 100% off grid solar system. The sun provides enough energy in my small yard for 2-3x my driving needs.
Solar panels can be engineered to also optimize cooling, by selectively increasing their reflectivity at wavelengths that are neither useful for electricity production nor for radiation of their waste thermal energy.
https://web.stanford.edu/group/fan/publication/Li_ACSPhotoni...
"[...] we design a photonic cooler made of one- dimensional photonic films that can strongly radiate heat through its thermal emission while also significantly reflecting the solar spectrum in the sub-band-gap and ultraviolet regimes. We show that applying this photonic cooler to a solar panel can lower the cell temperature by over 5.7 °C."
I remember seeing similar heat reduction claims in a more tropical, non desert env. https://reasonstobecheerful.world/green-corridors-medellin-c...
I think that's why Alabama despite all its flaws doesn't have quite as much projected warming as other southern states: lots of trees.
Does it really look different than say MS or georgia or the carolinas though?
As a matter of local trivia, today (2025.07.01) we had a wind storm in vegas that downed many trees. :)
I've just been presented with a captcha thingie asking me to select all things that can be picked up by a pair of chopsticks described as "the tool in the image"
Fuck off.
Then that vanished and another even more vapid effort appeared.
Fuck off.
If you need to piss around with this sort of nonsense, you probably shouldn't be entrusted with a website.
https://www.radware.com/products/bot-manager/
This seems to be the offending product being used, although the captchas themselves are standard hCaptcha.
i clicked the url and saw that first very weird looking captcha - then immediately closed the tab
looks like the archivers have trouble with it too; reminds me of the behavior of a virus with all the redirects lol
edit: for those with custom filterlists via ubo:
- ||iop.org
Archivers work fine for myself: https://archive.md/qUlES
There's also a direct PDF link https://iopscience.iop.org/article/10.1088/2752-5295/ade17d/... that also prompts for captcha (unless you arrive there via the web version)
Looping redirects on archive.XX urls often traces back to the use of Cloudflare DNS resolver .. the archive folk have some beef with Cloudflare over (?) handling privacy (?) and loop redirects on connections that arrive via that path.
It's a new captcha type for myself also. Interesting as it requires spatial reasoning and a bridge of understanding between text request and objects in images - although it falls to the usual farm of human captcha solvers.
nice, well i am using quad9; archive.org had 503's too (edit: lol i wonder if it did complete for me but somehow something else caused a loop - i never went to the search prompt afterward)
Is it just me, or has anyone also noticed that trees in southern climates closer to the equator (not jungles) have very few leaves and shade as opposed to trees in climates away from the equator (not tundras)?
What happens if you import northern US trees, the ones that produce a lot of shade, into southern states? Has this been tried?
It is also why there is very little shade in, say, Florida. Only occasional parts of the Martin Grade “scenic” highway look like a regular scene in the north.
The short answer is, they would die. The trees are the way they are because they've adapted to their environment. At a high level, trees in hot sunny areas will have smaller leaves because they can get enough sunlight from a smaller surface area, and smaller leaves lose less water.
But it is more complicated than that, of course. It's not just "how hot does it get", but also how much water is available, how windy it is, how cold it gets, and a million other environmental factors. That's why there is such a wide variety among the plants on earth.
(and yes, it has been tried. Check out the youtube channel "crime pays but botany doesn't")
Florida has plenty of shade, though you wouldn't know it considering our city planning. Anything that isn't too dense for humans is pure urban hellscape.
any group strategy to push back against the overuse of whole-page captchas ?
Do we all need to run an AI browser plugin now that auto-fills cloudflare captchas ?
Surprise surprise, vegetation is way better than concrete when it comes to being comfortable in a city
Not building your city in the desert is also a good idea when it comes to being a comfortable city.
It costs less to cool than to heat, by and large. And deserts have a lot of sunshine that can be converted into electricity for cooling...
But lack of water will become a huge problem when your city is growing that fast in a heating climate.
Edit: And cooling only works inside buildings or cars. Part of a comfortable city is being able to go outside and have a social life outside of a casino.
Municipal uses like drinking, showering, and watering ornamental plants is a tiny pct of desert water use. Most of it is crop irrigation, because if you can will water into existence then crops grow great in sunny deserts.
If the US' alfalfa exports to Saudi Arabia went down by 10%, we would never have a municipal water shortage in the American West in the next century.
Lack of water is a political problem. We have vast oceans which can be desalinated. Israel gets 85% of its water from desalination, they have gone from water shortages to having a water surplus.
We pump oil via pipelines vast distances, we can do the same with water.
We have virtually unlimited energy locked in Uranium which could power desalination plants, or heck you could power them with solar.
There’s plenty of water for the whole planet. There’s also plenty of clean energy (see nuclear and solar point earlier). But tapping these resources requires a functional government or at least a bureaucracy willing to allow companies to build.
There are people pushing for more shade in cities as an adaptation for a warming world. There is some crossover with the push for a reduction in cars and generally reducing the footprint of streets. Looking at old cities in hot climates I can see how this could make sense.
For Las Vegas, Cottonwoods are native and grow pretty quickly. Like many poplars they were used to grow shelterbelts.
I don't think anybody ever moved to Vegas expecting to be able to have a street life.
I used to hang out with my friends and neighbors outside all the time in Las Vegas.
...just not so much in May-August.
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That's a great idea, but hard for the city of Las Vegas to implement. Clark County doesn't have any ability to build a city not in a desert either. The state of Nevada doesn't have much of anywhere to put a non-desert city either.
Very few municipalities are willing to deny new residents, either. It wouldn't be anywhere on my list of viable places to live, but population growth in the Las Vegas metro area has been consistently large since 1910 until recently (only 10% growth from 2010 to 2020). The municipalities should likely invest in livability and comfort where possible.