7 ms·

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 ef

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.

idbehold 1y ago
Swamp coolers can't generally provide shade.
- jetru 1y ago
  I got a great business idea now.
zamadatix 1y ago
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.
- trhway 1y ago
  They do outdoor AC in [some places in some] parks in Qatar.
  - firesteelrain 1y ago
    Sounds like Qatar. Innovative and expensive.
    - saagarjha 1y ago
      Qatar is basically Vegas if it had more money.
  - chrisweekly 1y ago
    Under the sand on the beach, too!
- sandworm101 1y ago
  >> 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.
  - lmz 1y ago
    Also: Toronto's PATH - https://www.toronto.ca/explore-enjoy/visitor-toronto/path-torontos-downtown-pedestrian-walkway/ https://www.toronto.ca/explore-enjoy/visitor-toronto/path-to...
  - zamadatix 1y ago
    Cooling the streets is nothing like a mall or growing tbe walkway connections, those are much too sensible.
- sneak 1y ago
  If you cover the roof in solar, it will generate more than sufficient power to air condition it.
- gsf_emergency_2 1y ago
  >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: during the day, trees provide significant shade by intercepting solar radiation, reducing mean radiant temperature (up to 16 °C)
  - bmacho 1y ago
    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.
    - gsf_emergency_2 1y ago
      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-hydrogel-window-pulls-clean-drinking-water-from-dry-desert-air/ 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
    - bobthepanda 1y ago
      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.
cyberax 1y ago
There is literally no difference. Water is water, and its specific heat of evaporation doesn't depend on the way it's evaporated.
cryzinger 1y ago
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.
- photonthug 1y ago
  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 https://en.wikipedia.org/wiki/Windcatcher [2] https://en.wikipedia.org/wiki/Salsabil_(fountain) https://en.wikipedia.org/wiki/Salsabil_(fountain) [3] https://en.wikipedia.org/wiki/Passive_cooling https://en.wikipedia.org/wiki/Passive_cooling
  - cryzinger 1y ago
    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?
    - bigbacaloa 1y ago
      [dead]
    - 1y ago
obblekk 1y ago
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.
- wyldfire 1y ago
  > 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!
  - deleted 1y ago
    [deleted]
  - BLKNSLVR 1y ago
    Obligatory response to 'Freedom Units' for those who haven't seen it: https://www.youtube.com/watch?v=JYqfVE-fykk https://www.youtube.com/watch?v=JYqfVE-fykk
  - manmal 1y ago
    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.
    - jandrese 1y ago
      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.
      - 1y ago
PaulHoule 1y ago
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.
- sidewndr46 1y ago
  So an umbrella?
  - PaulHoule 1y ago
    Yeah, but like an umbrella made by something like Drexler's nanotechology.
    - gsf_emergency_2 1y ago
      How about something more ... Realistic https://www.thebrighterside.news/post/mits-high-tech-hydrogel-window-pulls-clean-drinking-water-from-dry-desert-air/ https://www.thebrighterside.news/post/mits-high-tech-hydroge...
      - bmacho 1y ago
        That's the opposite of a tree, which turns drinking water into nothing
        PaulHoule 1y ago
        "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.
metalman 1y ago
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 https://en.wikipedia.org/wiki/Photosynthesis
sandworm101 1y ago
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.
gsf_emergency_2 1y ago
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)
kkfx 1y ago
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.
- ninalanyon 1y ago
  > trees can't do nothing for buildings taller them them. Plant trees on top!
  - kkfx 1y ago
    Still not useful: facades remain exposed and so the largest thermal mass of the building.
aaron695 1y ago
[dead]
throwaway41597 1y ago
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.
- thimkerbell 1y ago
  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.
  - throwaway41597 1y ago
    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...).
- gsf_emergency_2 1y ago
  >Trees excel at harvesting water. Specifically, some kind of giant succulent would be best for arid climes https://en.wikipedia.org/wiki/Aloidendron_dichotomum https://en.wikipedia.org/wiki/Aloidendron_dichotomum
  - flakeoil 1y ago
    But they probably don't evaporate water and cool as much as other plants and trees.
antman 1y ago
Some of it is converted to chemical energy used for the tree’s growth etc chatgpt says 30-40%

idbehold 1y ago

Swamp coolers can't generally provide shade.

jetru 1y ago
I got a great business idea now.

zamadatix 1y ago

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.

trhway 1y ago
They do outdoor AC in [some places in some] parks in Qatar.
- firesteelrain 1y ago
  Sounds like Qatar. Innovative and expensive.
  - saagarjha 1y ago
    Qatar is basically Vegas if it had more money.
- chrisweekly 1y ago
  Under the sand on the beach, too!
sandworm101 1y ago
>> 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.
- lmz 1y ago
  Also: Toronto's PATH - https://www.toronto.ca/explore-enjoy/visitor-toronto/path-torontos-downtown-pedestrian-walkway/ https://www.toronto.ca/explore-enjoy/visitor-toronto/path-to...
- zamadatix 1y ago
  Cooling the streets is nothing like a mall or growing tbe walkway connections, those are much too sensible.
sneak 1y ago
If you cover the roof in solar, it will generate more than sufficient power to air condition it.
gsf_emergency_2 1y ago
>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: during the day, trees provide significant shade by intercepting solar radiation, reducing mean radiant temperature (up to 16 °C)
- bmacho 1y ago
  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.
  - gsf_emergency_2 1y ago
    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-hydrogel-window-pulls-clean-drinking-water-from-dry-desert-air/ 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
  - bobthepanda 1y ago
    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.

cyberax 1y ago

There is literally no difference. Water is water, and its specific heat of evaporation doesn't depend on the way it's evaporated.

cryzinger 1y ago

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.

photonthug 1y ago
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 https://en.wikipedia.org/wiki/Windcatcher [2] https://en.wikipedia.org/wiki/Salsabil_(fountain) https://en.wikipedia.org/wiki/Salsabil_(fountain) [3] https://en.wikipedia.org/wiki/Passive_cooling https://en.wikipedia.org/wiki/Passive_cooling
- cryzinger 1y ago
  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?
  - bigbacaloa 1y ago
    [dead]
  - 1y ago

obblekk 1y ago

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.

wyldfire 1y ago
> 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!
- deleted 1y ago
  [deleted]
- BLKNSLVR 1y ago
  Obligatory response to 'Freedom Units' for those who haven't seen it: https://www.youtube.com/watch?v=JYqfVE-fykk https://www.youtube.com/watch?v=JYqfVE-fykk
- manmal 1y ago
  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.
  - jandrese 1y ago
    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.
    - 1y ago

PaulHoule 1y ago

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.

sidewndr46 1y ago
So an umbrella?
- PaulHoule 1y ago
  Yeah, but like an umbrella made by something like Drexler's nanotechology.
  - gsf_emergency_2 1y ago
    How about something more ... Realistic https://www.thebrighterside.news/post/mits-high-tech-hydrogel-window-pulls-clean-drinking-water-from-dry-desert-air/ https://www.thebrighterside.news/post/mits-high-tech-hydroge...
    - bmacho 1y ago
      That's the opposite of a tree, which turns drinking water into nothing
      - PaulHoule 1y ago
        "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.

metalman 1y ago

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 https://en.wikipedia.org/wiki/Photosynthesis

sandworm101 1y ago

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.

gsf_emergency_2 1y ago

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)

kkfx 1y ago

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.

ninalanyon 1y ago
> trees can't do nothing for buildings taller them them. Plant trees on top!
- kkfx 1y ago
  Still not useful: facades remain exposed and so the largest thermal mass of the building.

aaron695 1y ago

[dead]

throwaway41597 1y ago

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.

thimkerbell 1y ago
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.
- throwaway41597 1y ago
  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...).
gsf_emergency_2 1y ago
>Trees excel at harvesting water. Specifically, some kind of giant succulent would be best for arid climes https://en.wikipedia.org/wiki/Aloidendron_dichotomum https://en.wikipedia.org/wiki/Aloidendron_dichotomum
- flakeoil 1y ago
  But they probably don't evaporate water and cool as much as other plants and trees.

antman 1y ago

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