Anecdata: I have a plot of land in the Santa Cruz Mountains and half of it has redwood coverage and the other half is sparsely covered by much smaller species. On hot days I can go to the redwood half and get an easy 10F temperature drop.
Shade is part of the equation and so is retaining water. Once I was introduced to the idea of check dams and their role in water conservation, I started noticing how the redwoods often build their own on hilly terrain.
The landscape in a forest can be quite complex and rich.
Can feel the same effect here in CA. I’ve heard that in areas with more humidity the effect is much weaker though, presumably because the air has higher heat capacity or something and so doesn’t cool as quickly in the shade.
I live in the Midwest US, plenty humid here in the summer but it’s consistently 5 degrees cooler in my wooded neighborhood than it is in the nearest town about 10 miles away. The effect is real.
Interesting. I asked a friend from Texas and he said he wasn't even aware that shade was cooler until he moved out. Need more data.
It’s not about shade alone. A cliff or single tree provides shade, but a forest provides evaporative cooling during the heat across a huge area alongside shade, it ends up a noticeably different climate.
There’s some other effects such as photosynthesis converting sunlight into chemical energy which in the short term is like reflecting that energy into the sky. At night plant metabolism warms the environment slightly and blocking the sky reduces radiative cooling to space, but that’s generally a good tradeoff for comfort.
Counterpoint: Shaded spots at work parking lots in Texas fill up the fastest. Conspicuously so. Also, use of windshield visors is much more prolific than in cooler climates.
I can't believe your Texan friend never noticed those phenomenon.
I don't respect your friend's observational skills. But to be pedantic, shades are cool because the sun does not heat up the air, but heats up the ground beneath you and it heats up the air. The water evaporated helps in cooling us down.
Might also have something to do with the ground and trees evaporating less water into the already humid air, reducing the cooling effect of evaporation.