Cities are very effective at trapping heat due to factors such as building density and paved surfaces. They are also a source of waste heat from vehicular traffic, heating, and air conditioning. In addition, opportunities for cooling from natural ventilation and evapotranspiration from vegetation may be limited because of the layout of the city and the lack of trees and green spaces. All of these factors result in urban areas being much hotter than their rural surroundings, especially during nighttime hours.  This is known as the urban heat island (UHI) effect. UHI effects have significant consequences for people’s health, particularly those living in disadvantaged communities. These effects are expected to worsen with climate change. City layout plays a major role in how heat is trapped and amplified.