What goes into urban planning? Potential for traffic density, the width and size of a road, perhaps recreational spots, and public transport connectivity. What doesn’t go into urban planning, however, is the potential for these sites to become ‘Urban Heat Islands’, and cauldrons trapping heat.
Lower building height and aligning streets against the sun’s path could prevent new layouts from heating up as much as dense core areas do, says a report by researchers from The Energy Research Institute (TERI). The observations made in the study, which was commissioned by Environmental Management & Policy Research Institute (EMPRI), were published by The Hindu on Friday.
As areas become dense, and narrow streets get flanked by buildings, ‘urban canyons’ that trap hear are created. They become heat islands that are significantly warmer during the day and night as compared to other areas with wide roads and parks.
Align roads in north-south direction
What could help in new layouts is to align roads in a North-South direction, rather than an East-West direction. This has not been a feature in any planning effort so far. For instance, Banashankari VI stage, developed by the Bangalore Development Authority, has a majority of streets in the East-West direction. Without large green canopies in streets such as these, the TERI report warns: “The axis of such streets coincides with the path travelled by the sun. Hence, such streets would keep receiving direct solar radiation throughout the day.”
However, in a North-South direction, the building height themselves provide shade for most part of the day, keeping the streets cooler.
Height of buildings
Another aspect of urban heat islands that has been ignored is the height of buildings. Currently, for roads less than 9 metres wide, the maximum building height has been kept at 11.5m (G+3floors), and most areas have built to this height or higher. As in the case of Basaveshwaranagar, this heats up the streets and traps heat.
“If the height of buildings is restricted to match the width of the road or lesser, then you can successfully mitigate urban heat islands. Parts of the road are shaded, and there is enough of a ‘sky view’ for the heat to escape at night, as is the case of Jayanagar, which is well-planned,” says Minni Sastry, TERI researcher who helmed the report.
However, these and other recommendations of sustainable development do not feature in byelaws or urban planning. “Zonal regulations and building byelaws currently do not address issues such as heat island effect. While areas already built will need to look at a retrofit, a more proactive approach must be used for the city's rapidly expanding peripheries,” says Rejeet Mathews, an urban planner with World Resources Institute.
White roofs can lower heat
A simple way for a city to fight the urban heat island effect is to go white. Or, at least on the roof.
TERI had earlier estimated that Bengaluru can save up to ₹1,034 crore in electricity cost if the roofs were painted white, to reflect solar radiation, rather than absorb it. The lower the heat absorbed, the lower the energy consumed for air-conditioners to artificially cool down the building.
“When the roof is lighter-coloured or white, more than 80% of the solar radiation is reflected back. But, darker coloured roofs end up contributing to urban heat island effects, and this heat remains trapped even in the night,” says Minni Sastry, a researcher from TERI.
In the nine areas of the city studied by TERI in 2017, less than 1% on average had white paint on the roof while up to 75% of roofs absorb heat in areas such as Basaveshwaranagar.
For areas such as Whitefield, where temperatures can be 4 degree Celsius above nearby areas, the open spaces, which are currently concreted, should be converted to permeable paving, vegetation or tree parks. The report observes that concrete open spaces (roads, parking lots) tend to absorb heat quickly in the day and release it equally quickly at night.
What experts suggest
“Using green roofs or permeable footpaths and other such techniques, we can reduce the heat stress in congested areas. We should start with a few demo streets, on the lines of TenderSURE roads,” says Minni Sastry, Associate Director, Sustainable Habitat Division, TERI.
“Land readjustment techniques (taking 50% of land for open space, and returning rest to plot owner) in the Karnataka Town and Country Planning Act has not been implemented. This micro-level planning can ensure that all new layouts preserve environmental features and reduce heat island effect,” says Rejeet Mathews, an urban planner with World Resources Institute.