Urban Atlanta can reach 5 to 8 degrees Fahrenheit or higher than surrounding rural areas. It also shows potential weather phenomenon created by Atlanta's sizeable urban heat island. Heat islands are created when city growth alters the urban fabric by substituting manmade asphalt roads and tar roofs and other features for forest growth.
Trees provide shade and cool the air through evaporation.
The hard, dark surfaces like pavement store heat during the day, heat that is then released at night, keeping the city hotter for longer periods of time. Air-conditioning is then kicked into overtime to combat the heat. The focus of research now is on the driving forces, magnitude and overall extent of the effect. One concern is the ability of urban heat islands to create or alter weather patterns - specifically to cause thunderstorm activity. The dome of heated air generates convective clouds that bring rain and thunderstorms.