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Urban Heat islands

Context:

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”.

  • Recently, two areas in Delhi recorded temperatures close to 50 degrees Celsius.

Relevance:

GS I- Geography

Dimensions of the Article:

  1. What is an urban heat island?
  2. Why are cities hotter than rural areas?
  3. How can urban heat islands be reduced?
  4. What has NASA said on urban heat islands in India?

What is an 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?

  • Larger green cover: Rural areas have relatively larger green cover in the form of plantations, farmlands, forests and trees as compared to urban spaces. This green cover plays a major role in regulating heat in its surroundings.
  • Transpiration : It 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.
  • Highrise buildings, roads in Urban areas: 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.
  • Heat absorption: 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.
  • NASA’s Ecosystem Spaceborne Thermal Radiometer Experiment (Ecostress) captured an image shortly, covering an area of about 12,350 square kilometres, which showed a large red patch around Delhi and smaller red patches around neighbouring cities of Sonipat, Panipat, Jind and Bhiwani.
  • These red patches, implying higher temperatures, were the heat islands, while the rural areas around the cities witnessing lower temperatures.

-Source: Indian Express

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