Of all the benefits to green roofs (increased efficiency, runoff control, longer life of the roof membrane), I've never seen any discussion of their connection to the heat island effect created in urban areas where there are lots of reflective building surfaces. Green roofs help keep the interior of a building cooler in the warmer months. Might they also help keep the surrounding area cooler since they don't bounce as much sunlight & heat off into the air? If so, and if enough buildings in an area had green roofs and other ground-level landscaping, we could probably create micro-climates in the city - places where the air temperature drops in the summer.
This is what happened in Center Plaza after it was redesigned. The old plaza was almost entirely concrete and in the summer it felt like a hotplate. It was miserable. The new space is grassy with young shade trees and gravel pathways. Last summer it was noticeably cooler than the surrounding streets and sidewalks.
-m.e.
The revamped Center Plaza.
