Several parts of the country are reeling under heat wave conditions. Cities, especially, are a lot hotter than rural areas. This is due to a phenomenon called an “urban heat island”.

Urban Heat Island

• An urban heat island is a local and temporary phenomenon experienced when certain pockets within a city experience higher heat load than surrounding or neighbouring areas on the same day.
• The variations are mainly due to heat remaining trapped within locations that often resemble concrete jungles.
• The temperature variation can range between 3 to 5 degrees Celsius.

Why are cities hotter than rural areas?

• Green cover: Rural areas have relatively larger green cover in the form of plantations, farmlands, forests and trees as compared to urban spaces.
• Transpiration: Transpiration is a natural way of heat regulation. This is the scientific process of roots absorbing water from the soil, storing it in the leaves and stems of plants, before processing it and releasing it in the form of water vapour.
• Heat-regulation: Urban areas are often developed with high-rise buildings, roads, parking spaces, pavements and transit routes for public transport. As a result, heat regulation is either completely absent or man-made.
• Construction: Cities usually have buildings constructed with glass, bricks, cement and concrete all of which are dark-coloured materials, meaning they attract and absorb higher heat content.

This forms temporary islands within cities where the heat remains trapped.

How can urban heat islands be reduced?

• The main way to cut heat load within urban areas is increasing the green cover; filling open spaces with trees and plants.
• Other ways of heat mitigation include appropriate choice of construction materials, promoting terrace and kitchen gardens, and painting white or light colours on terraces wherever possible to reflect heat.

What has NASA said on urban heat islands in India?

• NASA recently pointed out heat islands in urban parts of Delhi, where temperatures were far higher than nearby agricultural lands.
• It used its Ecosystem Spaceborne Thermal Radiometer Experiment (Ecostress) on the International Space Station.

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