[Answered] What do you understand by Urban Heat Island Effect? Highlight the factors that give rise to the phenomenon of Urban Heat Island.

An urban heat island is a local and temporary phenomenon. It is experienced when certain pockets within a city experience higher heat than neighboring areas in suburban or rural areas, on the same day. The temperature variation can range between 3 to 5 degrees Celsius. Urban-rural temperature differences are often largest during calm, clear evenings. This is because rural areas cool off faster at night than cities.

There are following factors that give rise to the phenomenon of Urban Heat Island:

• Transpiration is a natural way of heat regulation. But the urban areas lack sufficient green cover or gardens.
• The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight. This is called “urban canyon effect”.
• tall buildings also block the wind, which inhibits cooling by convection and prevents pollutants from dissipating. Waste heat from automobiles, air conditioning, industry, and other sources also contributes to the UHI.
• Cities usually have buildings constructed with glass, bricks, cement, and concrete- all of which are dark-colored materials, meaning they attract and absorb higher heat content. Thus, it forms temporary islands within cities where the heat remains trapped.
• The haze of air pollution that hangs over many cities can act as a miniature greenhouse layer, preventing outgoing thermal radiation (heat) from escaping from urban areas.

Way forward:

• Trees, green roofs and　vegetation can help reduce urban heat island effects by shading building surfaces, deflecting radiation from the sun and releasing moisture into the atmosphere.
• Other ways of heat mitigation include appropriate choice of construction materials, promoting terrace and kitchen gardens and painting light colours on terraces to reflect heat.