I´m trying to run some UHI and outdoor comfort studies on pedestrian crossings in the city of San Antonio TX, but when I run the hydra definition (After correcting an error from an empty generated weather file by deleting some numerical characters added to the name of the file in the study folder) the epw file modified with the Run UWG component seems to present lower temperatures from those of the airport file I´ve used. Would it be a problem with the way my geometry is set up? or could it be a problem with the EPW file?. (I tried all the available EPW´s available in the ladybug map with similar strange results, then I tried an Austin Tx EPW with more logical results).
I am attaching my rhino and Gh files.
Thanks in advance for your help.
Arturo2018_04_17_UHI_SanAntonio_LasFloresyCommerce.gh (972.9 KB)
2018_04_17_UHI_SanAntonio_LasFloresyCommerce.3dm (3.1 MB)
Lower average urban temperatures compared to rural temperatures are definitely a plausible scenario when you have an arid climate with more vegetation than the rural setting. The default rural conditions assume no trees (like an airport) so, when you add trees into your model like you have there, their evaportranspiration can cancel out much of the UHI effect, particularly because evaporative cooling is such an effective strategy in arid climates. You can change the amount of trees in the rural setting and this may give results that align more with your expectations (though this not necessarily more accurate). Decreasing the tree latent heat ratio would also align more with your expectations and might more accurately reflect the way desert plants tend to transpire.
I should also note that urban areas tend to have lower peak temperatures than rural areas just because of the thermal mass of the buildings in the urban canyon. UHI is largely a phenomena that happens after sunset and not right after noon when you have the hottest temperatures of the day.
Thank you very much for the clarification @chris, It does make sense once you consider the specifics of the site. I was definitely taking an over generalistic approach. I´ll move on to pedestrian comfort and microclimate maps now. Thanks again for all the amazing work you guys have been doing.
You’re welcome, @LUISARTUROREYESVALEN . Thanks for asking the question.