"Some Cities" is the most-arid quarter of cities - where greenery absorbs more solar energy than light surfaces, and water-conserving plant species do less evaporative cooling.

However trees - which both provide both shade and use their deeper root to keep up the evaporative cooling - were a net negative in only 2% of cities.

(Yeah, there are other reasons to avoid growing grass in hot, arid cities. Starting with the water supply.)