With regards to temperature, there are more levers to pull, like the aspect ratio of the street (narrower = cooler). Architects in Taiwan and southern China have been studying arcaded streets (qilou/騎樓), which seem to be as good as trees for shielding pedestrians [1], except in situations where the sun might shine through the sides or ends.
Of course, trees are great for many other reasons like air quality, but for temperature fundamentally they're just big evaporative coolers. I wish cities in more water-stressed areas would consider arcades + rooftop solar.
The big advantage trees have ove most man-made shade is that heat can convect through them. If you’ve ever sat underneath an umbrella at a café versus a beer garden under trees you’ll notice the difference. The umbrella shades, but traps reflected heat, re-radiating it below.
Trees also provide a significant cooling effect by releasing water vapour into the air from the soil (evapotranspiration), which you won't get under an umbrella.
Qilou seem much more oriented around shelter from the rain than for shelter from the sun, though. I agree that they're a great addition to urban streets for pedestrians!
Of course, trees are great for many other reasons like air quality, but for temperature fundamentally they're just big evaporative coolers. I wish cities in more water-stressed areas would consider arcades + rooftop solar.
[2] https://www.mdpi.com/2071-1050/11/5/1355/htm