The urban heat island (UHI) is the thermal increase urban areas experience relative to rural surroundings. The difference can reach 5–10 °C at night, when concrete, asphalt, and buildings release heat accumulated during the day.
Factors and mitigation
Contributors include the low albedo of dark surfaces, lack of vegetation (less evapotranspiration), waste heat from buildings/vehicles, and the geometry of urban canyons that traps radiation. In Madrid, the UHI can exceed 8 °C on calm summer nights. Mitigation strategies: reflective roofs and pavements, urban trees, parks, and fountains.