The Urban Heat Island (UHI) effect is created by the built infrastructure absorbing, trapping, and in some cases directly emitting heat. This results in the Melbourne metropolitan area having a climate significantly warmer than its rural surrounds. On clear and calm nights for example, temperatures can be up to 4°C hotter in the CBD; and with ongoing infill and greenfield growth UHI effects are expected to spread and intensify across the wider metropolitan area.

The UHI effect is expected to compound climate change impacts by intensifying heatwaves and extreme heat events. Of particular concern is the nocturnal impact of the UHI, with night-time heat retention strongly associated with deaths during extreme temperature events. Other impacts include: increases in electricity demand; lost workforce productivity; and rail system delays.  Green Infrastructure (GI), defined as living plant matter within the urban environment, is one approach to reducing urban heat. International studies suggest that a 10% increase in GI cover across a city could result in UHI reduction of up to 2.5°C.