Street trees raise the air temperature

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Mosaicinsights
Posts: 24
Joined: Tue Apr 21, 2020 1:12 am

Street trees raise the air temperature

Post by Mosaicinsights »

Hello,

I'm currently modelling an urban area in northern Australia, in the tropics on a 37˚C day. I have run multiple cooling scenarios including adding street trees and replacing roads with grass.

I've had some strange results that I can't explain. I found that adding street trees raised the air temperature at 1.5m above ground by more than 1C at 3pm where the trees were. In the UTCI there is a cooling effect directly under the tree because of shade but next to the tree there is a warming effect. I can't explain it.

In another scenario I replaced a building with grass which created a warming effect in the air temperature and UTCI near where the building was and I also replaced an asphalt road with grass which also created a warming effect in the air temperature (though a cooling effect in the UTCI).

It seems that my simulations using vegetation gave strange warming effects. In contrast, my simulations using water bodies, water fountains, misters, irrigation, cool roads and cool roofs all produced results as expected.

Could there be something about trees and grass in the tropics? In the past I've conducted similar simulations for southern Australia with a dry heat and got results that I would expect.

I've attached my project files for the control simulation and street trees simulation, as well as some figures I produced on the results at 1.5m above the ground. If you would like to see the model output please let me know.

Thank you for your time and help,
Steph
Attachments
Proserpine_control_temp_3pm.png
diff_Proserpine_street_trees_utci_3pm.png
diff_Proserpine_street_trees_temp_3pm.png
Proserpine_street_trees_temp_3pm.png
trees_proserpine.zip
(270.12 KiB) Downloaded 5 times
control_proserpine.zip
(265.35 KiB) Downloaded 3 times

Tim
Posts: 1868
Joined: Mon May 15, 2017 3:46 pm

Re: Street trees raise the air temperature

Post by Tim »

Hi Steph,

I initially thought that the wet conditions are probably the cause for that: less transpiration, less latent heat flux and thus no air temperature drop or even an air temperature increase due to the high leaf temperatures.
However, water sprays etc. would then also be less efficient and would even increase UTCI or PET values because it gets even more humid in addition to the heat. Since that is not the case I don't have a clue right now what could possibly be the reason.
I can only hint you to a paper where we described recent developments in our model, which will be released with the new ENVI-met version in summer: https://www.mdpi.com/1999-4907/11/8/869. The developments especially concentrate on the plants' behaviour depending on radiation. Maybe that is a rather unrealistic factor at the moment causing your strange simulation results.

Best regards,
Tim

Mosaicinsights
Posts: 24
Joined: Tue Apr 21, 2020 1:12 am

Re: Street trees raise the air temperature

Post by Mosaicinsights »

Hi Tim,

Thanks for sharing the article and I'll keep trying to find the reason for the results.

Thanks for your time,
Steph

Mosaicinsights
Posts: 24
Joined: Tue Apr 21, 2020 1:12 am

Re: Street trees raise the air temperature

Post by Mosaicinsights »

Hello again,

I'm still really confused by the results. Would it be possible if you ran the ENVI-met simulations for this area to see if you also get a warming effect from the street trees?

I'm asking because I work in environmental consulting and we are hoping to do lots of ENVI-met modelling in this part of Australia, it would be a shame if we can't use it in the future.

I would be interested if there is (hopefully) just something I am doing wrong. I made the trees in Albero, perhaps something went wrong there? The relevant files are attached in my first post on this topic.

Thanks for your time,
Steph

Tim
Posts: 1868
Joined: Mon May 15, 2017 3:46 pm

Re: Street trees raise the air temperature

Post by Tim »

Hi Steph,

I am afraid we don't have the capacity to run the simulations. What can do sometimes is debugging issues with models to see why the error occurs and hopefully being able to fix it then.

You may try different fixes by yourself: change the meteorological boundary conditions to those of the dry region and see if works then -> model area would be fine, issue is the meteorology. Change the LAD of trees and grass and see if the results are better with the same meteorological conditions -> met. conditions are fine, model area is problematic. There are too many options that may cause these results.

Best regards,
Tim

Wanlu
Posts: 22
Joined: Wed May 02, 2018 1:24 pm

Re: Street trees raise the air temperature

Post by Wanlu »

Hi Tim,

Would you mind telling me about the schedule of incoming new ENVI-met in summer version?
When will it be released? Thanks in advance!

Best,
Wanlu
Tim wrote: Wed Nov 11, 2020 6:07 pm Hi Steph,

I initially thought that the wet conditions are probably the cause for that: less transpiration, less latent heat flux and thus no air temperature drop or even an air temperature increase due to the high leaf temperatures.
However, water sprays etc. would then also be less efficient and would even increase UTCI or PET values because it gets even more humid in addition to the heat. Since that is not the case I don't have a clue right now what could possibly be the reason.
I can only hint you to a paper where we described recent developments in our model, which will be released with the new ENVI-met version in summer: https://www.mdpi.com/1999-4907/11/8/869. The developments especially concentrate on the plants' behaviour depending on radiation. Maybe that is a rather unrealistic factor at the moment causing your strange simulation results.

Best regards,
Tim

Tim
Posts: 1868
Joined: Mon May 15, 2017 3:46 pm

Re: Street trees raise the air temperature

Post by Tim »

Hi Wanlu,

The new version will probably be released around May.

Best regards,
Tim

Wanlu
Posts: 22
Joined: Wed May 02, 2018 1:24 pm

Re: Street trees raise the air temperature

Post by Wanlu »

Oh, I see. Thanks for your prompt response, Tim.
Tim wrote: Thu Nov 26, 2020 7:43 am Hi Wanlu,

The new version will probably be released around May.

Best regards,
Tim

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