When you are living in a city, you naturally feel the need to crank up the AC; whether at home or in your cars. In Delhi, summers can touch temperatures of 45 degree Celsius or more! But when you move to open spaces, where there is a bit of greenery, you immediately feel the change. There is a breeze that flows, you feel less suffocated and less “closed up”.
Why is that?
Heat islands, or Urban Heat Islands (UHI) are urban areas that are significantly hotter (1-3 degree Celsius) than surrounding rural areas. This effect is amplified during the evenings and night time than during the day. The cause of heat islands is the change in landscape in urban areas. As urban areas develop, we have more buildings, roads and pavement. This means more concrete. Concrete is a substance that is extremely dry and has the ability to heat up to extreme temperatures. It also does not store water within itself.
Because of the properties of concrete (and other substances like glass, that dominate urban landscapes), the urban area is characterized by dry, impermeable surface features. When the sun heats these surfaces up, they absorb the heat and rise up to extreme temperatures. This is why you can never walk barefoot on a pavement when the sun is at its peak. Also, whatever water was left on the surface evaporates very quickly.
As evening approaches, these substances slowly begin to release the heat that they had stored up in them. Slowly, is the key word here. The air, which is a poor conductor, traps this released heat around the urban area. As more heat is released into the night, more heat is stored by the air around the urban center. This drastically increases the air temperatures around the place.
Conversely, in rural landscapes, the land is dominated by grass or trampled roads. These surfaces do not absorb a lot of heat, instead they reflect most of it. Also, grasses have a lot of water stored in them that is constantly replenished as it is drawn from below the surface.
The release of heat in rural areas is faster. The added advantage in rural areas is the open spaces. There are no high rise buildings to stop the wind from blowing. Whatever heat is trapped by the overlying air, gets blown away by the winds. The result is much cooler nights.
Why does this matter?
The world is moving fast towards a more urban landscape. With cities spreading fast, we find more and more heat islands developing. This has a significant impact on our needs and way of life.
Increased temperatures throughout the day mean that we feel the need to keep our homes cool artificially. Energy requirements shoot up, especially during summers. Heat waves are intensified in urban areas, and many people can (and do) fall ill during the summers. The increased use of cooling equipment has side effects in the form of chemicals being released into the atmosphere. Also, heat islands have a marked effect on the open water quality in that area.
How can this be avoided?
The UHI effect can be minimized simply by planning the urban center better. During construction, care should be taken to ensure buildings are well spaced, and there is plenty of grassy surface around the buildings. Trees, if any, SHOULD NOT BE CUT DOWN. Shade areas are worth their space in gold, literally.
It’s also highly advisable to have roof-top gardens. This is a practice that is gaining popularity in many European cities. In fact, Beijing and Bangalore have gone one step ahead and developed vertical gardens in various places in the city. Plants are the solution to excess heat as well as air pollution; plant as many in as many places as possible.
If having gardens in rooftops is not an option, at least ensure there are reflecting surfaces on your rooftops. This can be mirrors, solar panels, metal sheets, etc. Increase the albedo (reflectivity) of the surface, and you reduce the amount of heat it absorbs. You can also do this to your cars by coloring your car in a light, bright color (at least the top. You can make a style statement too!).
The biggest reason to negate the heat island effect is to ensure your friends’ and families’ good health. It is deceptively dangerous, this effect. A few simple steps on your part can easily fix this problem.