Explained: What are urban heat islands, and why are they worsening during summers?

What is the News?

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

What are Urban Heat Islands?

An urban heat island is a local and temporary phenomenon experienced when certain pockets within a city experience a higher heat load than surrounding or neighbouring areas on the same day.

For example, a greener locality like Pashan in Pune often records cooler temperatures than urban areas like Shivajinagar, Chinchwad or Magarpatta.

The variations are mainly due to heat remaining trapped within locations that often resemble concrete jungles

Why are cities hotter than rural areas?

Rural areas are often covered with plants, grass, trees, and crops. Plants take up water from the ground and release it into the air as vapour through a process called transpiration which acts as nature’s air conditioner. Evaporation from water bodies also helps in cooling down these areas.

On the contrary, urban areas lack sufficient green cover or gardens and are often developed with highrise buildings, roads, parking spaces, pavements and transit routes for public transport. As a result, heat regulation is either completely absent or man-made.

Why do cities absorb more heat?

According to Physics, black or any dark-coloured object absorbs all wavelengths of light and converts them to heat, while white reflects it.

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 by increasing the green cover; filling open spaces with trees and plants.

Other ways of heat mitigation include the appropriate choice of construction materials, promoting terrace and kitchen gardens, and painting white or light colours on terraces wherever possible to reflect heat.

Source: The post is based on the article “Explained: What are urban heat islands, and why are they worsening during summers?” published in Indian Express on 18th May 2022.