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.
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) during the day, trees provide significant shade by intercepting solar radiation, reducing mean radiant temperature (up to 16 °C)
Only ambient sunlight needed here, but they'd have to make the panels vertical
https://www.thebrighterside.news/post/mits-high-tech-hydroge...
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.
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.