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18th May 2022 (8 Topics)

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”.

About

What is an urban heat island?

  • An urban heat island occurs when a city experiences much warmer temperatures than nearby rural areas.
  • The difference in temperature between urban and less-developed rural areas is understood as how well the surfaces in each environment absorb and hold heat.

Why does this happen?

  • An urban area is a city and a rural area is out in the city areas. The sun’s heat and light reach the city and the villages in the same way. The difference comes in holding that heat of insolation.
  • Plants take up water from the ground through their roots and release in the atmosphere again. This process is called transpiration. It acts as nature’s air conditioner.
  • While urban areas lack in plants and trees around them, the air conditioning happens minimal.

Why it occurs only in urban areas?

  • Due to Buildings: materials such as asphalt, steel, and brick are often very dark colours—like black, brown and grey. A dark object absorbs all wavelengths of light energy and converts them into heat, so the object gets warm.
  • Due to pollution: urban areas are more exposed to vehicle pollution and industrial one. Due to this the air gets warm and phenomenon like ‘ground ozone’ takes place.
  • Large population: more population density in urban areas makes them more prone to human induced pollution and makes the area exposed to more waste generation, livelihood practices etc.

Mitigating measures

  • To cool down urban heat islands, some cities are ‘lightening’ streets. This is done by covering black asphalt streets, parking lots, and dark roofs with a more reflective gray coating. These changes can drop urban air temperatures dramatically, especially during the heat of summer.
  • Planting gardens on urban rooftops can also help to cool down the city.
  • Builders can use materials that will allow water to flow through. These building materials—called permeable materials—promote the capture and flow of water, which cools urban regions.
  • Scientists can use this information to track hotspots in cities across the planet. NASA scientists, with their global satellite views, are working to understand urban heat islands and help urban planners to build more energy efficient, cooler and safer cities.

Impacts of urban heat islands

  • Leads to climate change: Urban heat islands are one of the easiest ways to see how human impact can change our planet.
  • Ecological impacts: Earth-observing satellites, such as Landsat and Suomi-NPP, keeping a close eye on heat pattern in urban areas. It shows that urban heat can affect human health, animals and can destroy crops.
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