Urban Heat Island: What Are They?


Firstly, to begin with let us define what urban heat islands are. Urban heat islands are metropolitan areas of land that are warmer or higher in temperature than their surrounding rural areas due to human activities. According to the US environmental protection agency “The annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C).” This change is majorly seen during summer time when temperatures are high and resulting is a rise in demand for energy consuming products such as air conditioners.

As urbanisation, globalisation occur and the number of people living in an area expand, more space is required, and as these urban areas develop due to industrialisation, vegetation and green land is replaced by buildings and other infrastructure. The temperatures on theses heat land are rather low during the early mornings and during the duration if the day and become more pronounced after sunset as these buildings begin to radiate heat into the atmosphere thereby increasing the temperature.

There are two types of Urban Heat Islands

  • Canopy Layer Heat Islands: This refers to the layer of air which directly affects us, it spreads from the surface of the ground to the height of trees and buildings
  • Boundary Layer Heat Islands: This boundary begins from the end of the canopy layer, that is from the top of buildings and tree tops to about a mile above in the atmosphere.

How do they affect us?

During summer when the temperatures are high, the temperatures further elevate in urban heat islands and tend to result in a negative way on the quality of life on people and the environment. Some other factors that have been noticed that are a negative impact on the environment and our lives as a result of urban heat islands are:

  • Increase in the level of energy consumption: In metropolitan cities during the summer season, the consumption for electricity rises anywhere from 5% to 12% due to the rise in demand for cooling, thereby, putting pressure on the energy consumption units.


  • Increased amount of release in greenhouse gases and pollutants: Increasing demand for energy results in emission of greenhouse gases and pollutants into the atmosphere which also results in depletion of the ozone layer.


  • Alteration in human health and comfort: With rise in temperatures drastically it has several impacts in health conditions. It may lead to fatigue, het strokes and respiratory diseases.


  • Reduction in the quality of water: According to the US EAP “Hot pavement and rooftop surfaces transfer their excess heat to storm water, which then drains into storm sewers and raises water temperatures as it is released into streams, rivers, ponds, and lakes. Rapid temperature changes can be stressful to aquatic ecosystems.”


These are some of the main recognised reasons and the ways in which Urban Heat Islands affect out lifestyle and health apart from the ecosystem itself.


What are the solutions..

We have recognised and sorted out the problem that we may face in Urban Heat Islands, How they are caused, now we look at what we could possibly do to retain a balanced ecosystem and how we can achieve it.

Some of the few ways or solutions that have been useful in maintaining normal temperatures and lifestyles on Urban Heat Islands are as follows:

  1. Planting more trees in urban areas and increasing the vegetation cover
  2. Creation of roof top gardens and eco roofs
  3. Installing sun reflective roof tops
  4. Installing cool pavements

Some of these are voluntary actions and some are to be done by policy change. For example, maintaining roof top gardens and cool pavements is a voluntary action by individuals, an effort to be made by them to retain balance in the ecosystem, whereas, some of them are to be changed by policy like installing sun reflective roof tops for industries mandatory.

The last most important concept to discuss is how the weather has an impact on these Urban Heat Islands. During the season of summer, Urban Heat Island are said to be more intense due to the clear sky and calm winds. Though at the time of monsoon the clouds are overcast and the winds are fierce, causing the temperature to vary and stop the rays of the sun into penetrating onto the surface of the earth. There by keeping these areas cooler.

I guess it is about time that we took into account that our actions directly or indirectly affect the environment around us. It is also a huge threat to our health system. If we do not wake up early enough and realise that things are taking a wrong turn faster than we are able to record, it is time we began to stop being a catalyst of the process. One individual’s effort could probably save one person’s life. Think about it.


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