Climate Change Impact on India and World – International Reports, Key Observations, etc.

Urban areas cooler than non-urban regions during heat waves

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Mains Paper 1: Social Issues | Urbanization, their problems & remedies

From the UPSC perspective, the following things are important:

Prelims level: Urban Heat Island Effect

Mains level: Impact of Heat waves


News

  • A study of 89 urban areas in India has found that though there is an absolute increase in temperature during heat waves in both urban and non-urban areas, the urban areas are relatively cooler than the surrounding non-urban areas.

Urban areas Heat lesser

  • At 1.94°C, the absolute increase in temperature during the day in non-urban areas during a heat wave was significantly higher than in urban areas (0.14°C).
  • According to the analysis, urban areas were found to be relatively cooler than the surrounding non-urban areas during heat waves.
  • At 44.5°C, the non-urban areas were warmer than urban areas (43.7°C).
  • However, during the night, all urban areas were hotter than the surrounding non-urban areas.
  • This result was quite unexpected.

Why?

  • The urban areas witness less temperature increase during heat waves compared with non-urban areas due to significantly higher tree cover and more number of water bodies.
  • In contrast, a majority of non-urban areas are located in agriculture-dominated regions.
  • In non-urban areas, the vegetation cover in the form of crops and soil moisture from cropland irrigation decline sharply after crops are harvested and well before the onset of heat waves during summer.
  • The urban areas, on the other hand, have perennial vegetation in the form of tree cover and lawns, and more number of water bodies, which help in keeping the urban areas relatively cooler than non-urban areas.

Back2Basics

Urban Heat Island Effect

An urban heat island (UHI) is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. This effect is known as Urban Heat Island effect.

Causes of UHI Effect

  • Heavy vehicular and industrial pollution in urban areas.
  • Discharge of greenhouse gases (GHGs) in substantial amounts, which trap the outgoing infrared radiations.
  • Tall buildings and other infrastructure which obstruct the flow of wind, consequently obstructing the transfer of heat.
  • Lack of vegetation which can act as both heat and carbon sink.
  • Majority of urban surfaces are composed of metal, glass, concrete or asphalt. These materials have high heat retaining capacity during the day and emit this heat out during the night.
  • The inability of water to penetrate the above materials, makes the urban landscape behave as a desert landscape.
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