Bring out the causes for the formation of heat islands in the urban habitat of the world.

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Ghissu Editorial · Accepted Answer

Urban heat islands form because cities absorb and store more heat in low-albedo materials, lose evaporative cooling as green and blue cover vanishes, trap radiation in urban canyons and add waste heat. Timothy Oke showed that heat-island intensity rises with city population.

**Introduction**

An urban heat island is a city markedly warmer than its rural surroundings, especially on calm, clear nights. The city absorbs and stores more heat, loses less by evaporation and adds heat of its own.

**Surface and Built-Form Causes**

FIGURE: geography-p26-0 | Temperature profile peaking over the dense downtown and falling towards rural edges

1. **Heat-absorbing materials**: Low-albedo asphalt, concrete and dark roofs absorb sunlight by day and release the stored heat slowly at night.
2. **Loss of green and blue cover**: Replacing trees and lakes with built surfaces removes evapotranspiration cooling, as the loss of Bengaluru's lakes shows.
3. **Urban canyons**: Tall, closely packed buildings trap longwave radiation and block cooling winds in cores such as Manhattan and Mumbai.
4. **Impervious surfaces**: Paved ground sheds rainwater into drains, so little energy goes into evaporation.

**Human and Atmospheric Causes**

1. **Waste heat**: Vehicles, industry and air conditioners release heat directly, and air-conditioner exhaust creates a feedback loop of more heat and more cooling demand.
2. **Pollution dome**: Aerosols and greenhouse gases over cities such as Delhi trap outgoing radiation and keep nights warm.
3. **City size**: Timothy Oke showed that heat-island intensity rises with population, so megacities like Tokyo and Delhi run hotter cores.
4. **Calm weather**: Clear skies and weak winds under anticyclones stop city and rural air from mixing, letting the heat island peak.

**Conclusion**

Heat islands are a human-made climate created by building materials, urban form and energy use. Ahmedabad's Heat Action Plan of 2013 and Telangana's Cool Roofs Policy of 2023 show they can be reversed.

Bring out the causes for the formation of heat islands in the urban habitat of the world.

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