“Cities in general tend to be hotter than their natural surroundings, thanks to a phenomenon known as the urban heat island.
‘If you have less green cover, you will almost always have higher temperatures, and greater exposure to heat,’ says Brian Stone, director of the urban climate lab at the Georgia Institute of Technology.
Trees provide shade, but they also cool the environment down through the evaporation of water from their leaves — a process similar to how humans sweat to cool down.
‘When you pave over an area, particularly if it had green plants, you have interrupted that cycle,’ Stone says. ‘Not only have you sealed the surface, you have put a lid on it, so evaporation cannot happen.’
Pavement — particularly if it’s black — absorbs heat and holds it in. At night, a city of more than 1 million people can be as much as 22 degrees warmer than its surroundings. Even the buildings themselves, Stone says, can create a sort of canyon that traps heat.”
— NPR