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Writer's pictureRajalakshmi Dhandapani

Urban Heat Island

Updated: Aug 13, 2023

Normally, when we travel to different locations by road or train, we might have experienced a warm urban area compared to cooler rural area. You might be thinking this is normal right... urban areas does not have much vegetation so obviously, they are going to have more temperature compared to adjoining rural area. The guess is right..


Normally, the highly urbanized area that has more air temperature compared to the nearby rural area will form a heat island, that we call it as Urban Heat Island. It will feel like in Fig.1. where urban people will experience a hot day compared to rural people in the adjacent area.

Fig. 1. Urban Heat Island

Image credit: NASA/JPL-Caltech


Let us discuss the science behind this ....

When the solar radiation reaches the surface it is uniform in both urban and rural area, but when the buildings absorb them, due to their property of absorbing more radiation and holding heat for a long time, less evapotranspiration to dissipate excess heat, along with transportation heat, results in more air temperature, while in rural area more evapotranspiration takes place, to dissipate the excess heat due to the presence of more vegetation.

In the Fig. 2 . you can easily see the difference in air temperature over different areas and the maximum temperature is in highly urbanized area.


Fig. 2. Air temperature over different areas



If you ask, is there a way to reduce this urban heat island so the urbanized people can also experience less heat. Yes, to some extent the temperature of the urban area can be reduced by changing the building materials that absorbs and hold less heat, changing the urban structure for free wind flow and by increasing the vegetation.


There are much research going on about this Urban Heat Island and ways to alleviate them. If you are more interested, do read the document in the link provided: https://www.construction.basf.us/files/pdf/BasicsCompendium.pdf


Stay tuned to know more about the science that we live with!







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2 commentaires


Thanks.

Yes, transpiration also reduces plant temperature and it's surroundings, similar to that of evaporation. The difference between evaporation and transpiration is evaporation is taking place from a physical surface and transpiration is from vegetation. Both has same effect in reducing the temperature, by taking the heat away from the contact surface. As air is heated from the contact surface, when evaporation or transpiration occurs it removes the heat and reduces the respective bodies temperature and it's surrounding air.

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A P PRAKASHAN
28 oct. 2020

A very relevant topic. Evaporation from a water body brings cooling..is it in the same way transpiration from the plant makes the surrounding cooling?

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