Urban Heat Island


Urban Heat Island Effect (UHI) is a phenomenon in which a particular area experiences warmer temperature than the surrounding rural areas. Urban regions show this particular climatic pattern when compared to rural regions. The phenomenon is particularly notable in summer and winter. Also, this is more apparent when the wind is less. It occurs both during day and night, and in some cities, night time is more prevalent. Heatwaves occur on the surface and in the atmosphere. Developmental changes due to industrialization led to less vegetation. Many environmental problems including climate change have resulted in this and eventually led to the occurrence of heatwaves. There is no absolute definition though, the heatwave is termed as a definitive period of high temperature. Densely populated, densely constructed, less vegetative urban regions produce waste heat and makes the region heat island.

1.Causes of Urban Heat Island

  • 1.1.Land modification: In reality, deforestation is extensively carried out for urbanization and industrialization. Tall concrete buildings in urban cities block the wind. Less convection is reported as the heat trapped cannot be blown out. This intensifies the heat waves. The materials used in the construction of roofs and pavements also increase air temperature. The arrangement and shape of buildings all contribute to the increase in temperature.
  • 1.2.Urban haze of pollution: Polluted air is an important factor. Exhaust gases from vehicles and industrial pollutants trap solar radiation. These pollutants act as a layer preventing heat from escaping.
  • 1.3.Decreased vegetation: The absence of enough trees and plants is of course an obvious reason. The process of transpiration from leaves is nature’s airconditioning. As a matter of fact, fewer plants and trees leave no room for the process.
  • 1.4.Concrete effects: Concrete areas in urban regions have enough surfaces for absorption and reflection of sunlight increasing the heat waves This is urban canyon effect.
  • 1.5.Anthropogenic heat: Heat released from the burning of fossil fuels.
  • 1.6.Waste heat:  Lastly, urban heat island can be also from waste heat. The heat produced by electrical and industrial machinery, in addition to incandescent light bulbs, refrigerators, air conditioners all contribute to waste heat. In most cases, they have lower utility.
Comparison of temperature difference

2. Consequences

Nature shows its resistance to the environment atrocities of humans in many ways. Urban heat islands are, of course, just one among them. They have far-reaching consequences in the environment and in turn to all life on earth.

    • Impact on climate.
    • Extended seasons
    • Decreased air quality
    • Impaired water quality
    • Increased energy usage
    • Health effects

High air pollution reduces night-time cooling resulting in warmer temperature at night. It brings out secondary effects on climate and seasons. Increased temperature leads to more energy consumption. This in turn leads to climatic changes and global warming. Likewise, it adversely affects animals and aquatic organisms whose body temperature plays a major role in metabolism, breeding, and reproduction. At the same time, it also obviously affects humans leading to heatstroke, heat exhaustion, heat cramps.

2.1.Heat-induced mortality:  Heatwaves have become more frequent due to an extreme increase in temperature. This results in heat deaths across the globe every year. They also aggravate recurring illnesses. Orissa, Rajasthan, Bihar, Maharashtra, together with Andhra Pradesh, and Uttar Pradesh had recorded the highest cases of heatwave related death and other issues last year.

2.1.1 Relation between heat island and Global warming:

Heat islands show a difference in local temperature. Nonetheless, global warming is the gradual rise in the surface temperature of the earth. Heat islands result in the emission of heat-trapping greenhouse gases which leads to global warming.  Strategies to reduce heat islands, therefore, can in turn reduce the emissions that contribute to global warming.

heat waves
Temperature in different regions
1.2.3.Main Urban heat islands in India:
    1. Mumbai
    2. Delhi(Know in detail about heatwaves in Delhi):
    3. Chennai
    4. Calcutta
    5. Bangalore
urban heat island
Aerial view of an urbanized city

3. Mitigation measures:

  • Use of sustainable building materials with less heat-absorbing capacity. National Mission on Sustainable Habitat is aimed at such a transition.
  • Building Material and Technology Promotion Council promote alternate material and construction technologies.
  • Increase vegetation and tree covers.
  • Include more water bodies within cities.
  • Use green roofs and cool roofs that reduce heat absorption. West Indian city of Ahmedabad, in Gujarat, is an example where cool roofs can be found.

3.1. The need of the hour: Ofcourse, plant more trees without fail. They clean the surrounding air by absorbing pollutant gases. Furthermore, they also help in preventing water pollution and soil erosion. Not to mention, trees also combat climate change.


cooler areas in urban heat islands

The graphics show how open land, greenery, and water bodies can create cooler areas in urban heat islands.


In addition to all these measures, the government of India recently implemented Smart cities’ mission for urban renewal and retrofitting programs to make the country more sustainable. Union Ministry of Urban Development carries out the mission in collaboration with various state governments. Hundred cities are selected altogether under the mission. This comprises at least one from each state. Then again, when nature shows its protest towards human atrocities in various ways, it is our duty to make possible positive efforts, before it is too late.

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