Heights and heat
Excessive opacity of high-rise structures results in creation of urban heat islands in cities
Internationally, a building that reaches or exceeds the height of 150 metres is considered a skyscraper. Until recently, Mumbai was the only Indian city with high-rise buildings. The financial capital continues to see the highest demand for skyscrapers, as the only option to grow there is vertically. It now seems that in the coming decade, Maximum City will receive an even more cohesive skyline, with a host of projects in the race to touch the sky being constructed. The demand for high-rise buildings is certainly growing, and other cities are catching up.
Mumbai continues to have the maximum number of tall buildings approved or under construction. Development of India One - the tallest in the country - has already begun in Maximum City. It spans 126 floors and stretches up to a height of 720 metres. Apart from this, Mumbai has more than 30 such super-tall buildings ranging between the heights of 150 metres and 450 metres either at the approval stage or already under construction.
New Delhi has around a dozen of such buildings coming up. They range between heights of 150 metres and 300 metres. Kolkata ,too, is catching up with nine such residential buildings extending to the height of 245 metres either approved or under construction.
Ahmedabad has about 13 tall buildings which are under construction range between 200 metres to 410 metres. Hyderabad and Bangalore, too, are witnessing some development in construction of tall buildings for residential-commercial purpose with two or three approved projects.
All i n all, t his amounts t o around 60 skyscrapers. Developers see such edifices as a good way to attract potential buyers – high- rise buildings are a good gambit to differentiate their offerings from the rest of the pack. However, this coin has two sides – high-rise development has its own share of demerits, too:
Increased urban temperature
Size and density of the built-up areas affect temperatures of urban areas. In the congested centres of large cities, temperature levels are generally higher than in the suburbs. The largest elevations of urban temperature occur during clear and still-air nights, also called urban heat island. Excessive opacity of high-rise buildings in city centres results in concentrated heat generation by high-density land use (traffic, lighting, heat exhaust) and contributes to the creation of urban heat islands.
Effect on night-time cooling
Nocturnal radiation is a major climatic factor that reduces atmospheric heat in urban areas located in hot, dry regions. Nocturnal radiation decreases when the density and the height of builtup urban masses increase.
High- rise buildings store solar energy during the day time and release it slowly into low-speed local wind, especially at night. The vertical distance between cool winds above building roofs and the ground surface is long, and this results in decreased radiant cooling during the nights.
Low- ri se buildings t hat match the heights of trees –1215 metres, on the other hand, penetrate night-time ventilated cooling at the ground level and also store cool radiation through built-up urban areas.