Urban Heat Islands (UHI) are urbanized areas that experience higher temperatures than outlying areas. Structures such as buildings, roads, and other infrastructure absorb and re-emit the sun’s heat more than natural landscapes such as forests and water bodies. Urban areas, where these structures are highly concentrated and greenery is limited, become “islands” of higher temperatures relative to outlying areas. It increases the demand for energy, leads to increased greenhouse gases emissions, discomforts human health and even affects the health of flora and funa. The major factors responsible for UHI

• Anthropogenic heat discharges: Sources of anthropogenic heat include cooling and heating buildings, manufacturing, transportation, and lighting. Heat from these sources warm the urban atmosphere by conduction, convection, and radiation.
• Absorption of heat: Paved over surfaces, such as roads and parking lots, absorb solar radiation as heat. Since these surfaces are impermeable, even water runoff is redirected to the stormwater system rather than being absorbed by plants or water bodies that help cool the area through evapotranspiration and evaporation.
• Urban geometry: The height and spacing of buildings affects the amount of radiation received and emitted by urban infrastructure. The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the intensity with which urban areas are heated. High rise buildings also trap outgoing radiation.
• Greenhouse effect: Carbon dioxide (CO2) and other greenhouse gases act like a blanket, absorbing IR radiation and preventing it from escaping into outer space.
• Lack of vegetation: Scant natural vegetation in urban regions reduces the natural cooling effect from the shade and evapotranspiration.

Measures that can be taken to countering UHIS:

• Promoting natural vegetation: Natural ventilation is one of the most effective passive cooling techniques. It can be done by arranging the openings in buildings to face the prevailing wind, ventilated roofs and building orientation with adequate gaps for good airflow.
• Use of appropriate surface material: An increase in the surface albedo has a direct impact on the energy balance of a building. Surface materials with a high albedo index to solar radiation reduce the amount of energy absorbed through building envelopes and urban structures, and keep the surface cooler.
• Use of white pavement instead of Asphalt: Asphalt temperature can reach 63°C and white pavements only reach 45°C. Lower surface temperatures contribute to decreasing the temperature of the ambient air because the heat convection intensity from a cooler surface is lower.
• Providing appropriate landscape: Providing an appropriate landscape in building can also contribute to energy consumption reduction. It can be done by making vertical and horizontal green spaces in different layers or floors of buildings with a multi-use function, which can significantly decrease the energy required to cool buildings.

Activities to reduce heat islands range from voluntary initiatives, such as cool pavement demonstration projects, to policy actions, such as requiring cool roofs via building codes. Most mitigation activities have multiple benefits, including cleaner air, improved human health and comfort, reduced energy costs, and lower greenhouse gas emissions. Heat island mitigation can also help cities reduce the impacts of climate change.