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.

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.

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.

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.

Some of it is converted to chemical energy used for the tree’s growth etc chatgpt says 30-40%

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.

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)

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.

Swamp coolers can't generally provide shade.

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.

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.

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

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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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.

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

oaks are at home in the Levante , syria, turkey Lebanon and spain - all partially desert places now, but oak foerested in the past.

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.

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.

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

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.

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

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.

what does he do?

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.

Does it really look different than say MS or georgia or the carolinas though?

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

https://www.radware.com/products/bot-manager/

This seems to be the offending product being used, although the captchas themselves are standard hCaptcha.

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."

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.

Not building your city in the desert is also a good idea when it comes to being a comfortable city.