At 2 p.m., when the sun is at its unrelenting brightest on a late winter day, the mercury level in the narrow, congested lanes of Basaveshwaranagar touches 31 degree Celsius. At the same time, in the narrow, congested lanes of Bellandur on the other side of the city, the temperature is nearly 4 degree Celsius lower.
While people in Bellandur, or other residential areas, suffer through peak temperatures for an hour, those living or working in Basaveshwaranagar have to put with peak temperatures for nearly five hours .
While an increasingly concretised Bengaluru is warming up — longer, hotter summers with shorter winters — a report by The Energy Research Institute (TERI) throws light on the complex factors that create ‘Urban Heat Islands’, that is, facets of ‘development’ which see some areas heat up much more than others.
Comparing residential locations of Bellandur, Basaveswaranagar, Koramangala, HSR Layout, Jayanagar as well as commercial areas of Marathahalli, Whitefield, Electronics City, TERI researchers Minni Sastry, Hara Kumar Varma and Vini Halve believe it is a combination of building height, road width, type of roof, open spaces, green cover and lakes that determine local temperatures. The trio were commissioned by the State-run Environmental Management & Policy Research Institute (EMPRI) to carry out the study.
The starkest observations come from Basaveshwaranagar, which like many areas in the city, is not close to a water body, has few open spaces (just 4% of the landscape) or green cover (2%). The roads are typically 6 metres in width, flanked by buildings that are around 9-12 metres high. More than three-fourths of the roofs are ‘conventional’, meaning that the darker-coloured rooftops absorb heat, rather than reflect solar radiation like white-coloured roofs do.
The streets, in essence, become a urban canyon, trapping heat.
“The characteristic of an urban heat island effect is a sky view factor. Basaveshwaranagar is a typical example, especially when compared to the green, well-planned Jayanagar or Bellandur, which has a lake nearby,” says Ms. Sastry. “With little open space or even a view of the sky from the streets for the heat to dissipate, temperatures rise for most of the day. Because heat is trapped and has no where to go, the area is warmer even at night, and hence more energy is consumed for ACs.”
In Jayanagar, the wide roads and green cover see the area heat up slower through the day, and peaks only at 4 p.m., compared to Basaveshwaranagar that peaks at noon and stays that way till around 5 p.m.
Similarly, a comparison of Koramanagala, HSR Layout and Jayanagar I Block — all of which have wide roads, canopy of trees and near-similar density of green — shows that Koramangala and HSR Layout benefit greatly by the presence of lakes, particularly at night when Jayanagar is 1.5 degree Celsius warmer than the other two localities.