In news: A recent study from IIT Kharagpur noted that anthropogenic forcing is exacerbating the urban heat islands in India.

Concept of Urban heat island (UHI)

  • It is where the temperature in a densely populated city is as much as 2 degrees higher than suburban or rural areas.
  • This happens because of the materials used for pavements, roads and roofs, such as concrete, asphalt (tar) and bricks, which are opaque, do not transmit light, but have higher heat capacity and thermal conductivity than rural areas, which have more open space, trees and grass. 
  • The lack of such evapotranspiration in the city leads to the city experiencing higher temperature than its surroundings.


Air Quality Index:

  • The National Air Quality Index (AQI) was launched in New Delhi on September 17, 2014, under the Swachh Bharat Abhiyan.
  • The Central Pollution Control Board along with State Pollution Control Boards has been operating National Air Monitoring Program (NAMP) covering 240 cities in the country having more than 342 monitoring stations.
  • It is used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become
  • It has 6 categories and covers 8 major pollutants.

Image Source: epa.gov


  • Trees and plants are characterised by their ‘evapotranspiration’ wherein evaporation involves the movement of water to the surrounding air, 
  • Transpiration refers to the movement of water within a plant and the subsequent lot of water through the stomata (pores found on the leaf surface) in its leaves. 


Impacts of UHI effect

On Air quality

  • With the addition of pollution generated by industrial and automobile exhaust it results in a higher extent of particulate matter and greater amounts of dust than in rural areas

On balance of ecology

  • The UHI increases the colonisation of species that like warm temperatures, such as lizards and geckos. 
  • Insects such as ants are more abundant here than in rural areas; these are referred to as ectotherms. 

On human and animal health

  • UHI effect leads to the emergence of heat waves which affect human and animal health, leading to heat cramps, sleep deprivation and increased mortality rates. 

On urban water bodies

  • As warmer water is transferred from the city to drains in sewers, and released into nearby lakes and creeks, it impairs their water quality.


Control of UHIs and mitigation

  • Using light-colored concrete (using limestone aggregates along with asphalt (or tar) making the road surface greyish or even pinkish (as some places in the US have done); these are 50?tter than black, since they absorb less heat and reflect more sunlight. 
  • Painting rooftops green, and installing solar panels there amidst a green background.
  • Planting as many trees and plants as possible.