It can be an easy thing to test yourself, depending on local geography. Go for a walk in a forested area, even lightly, and then walk in an open field, then walk on a street. The temperature difference is easy to notice.

There's a trail nearby that goes from lightly forested to pavement next to a road, and then back to lightly forested. There's easily a 5-10*c difference when on the pavement, it's like hitting a wall of heat.

Edit: this is to say: there should be no doubt about the effectiveness and necessity of urban tree cover. Green walls/roofs, light coloured roofs, green covered parking lots, etc. Solar panels also work well to block the sun, and provide extra power as well.