URBAN HEAT TRAP (Syllabus: GS Paper 3 - Env & Eco)

Context: Rising episodes and increasing intensity of heat waves have become quite common and a major problem in Indian cities.

• Urban India is a heat trap, but road orientation, building materials and zone-specific master plans can drastically enhance thermal comfort.

Factors responsible

• Urban morphology: The worst morphology turned out to be large low rise (industrial), mainly due to use of heat-trapping roofing materials like asbestos, galvanised iron sheets and plastic sheets.
• Aspect ratio (degree of direct sun exposure): The ratio of building height and street width plays a role in how much heat will be trapped by the roads, pavements and building surfaces. 

• The higher the aspect ratio, the lower the land surface temperature (LST). 

• This means the narrower the street, the lesser the heat gain. 
• Buildings shade each other and decrease direct exposure of surfaces to the sun.
• Floor space index: LST increase as FSI decrease.
• Cities define the extent of construction on a plot through FSI.
• Street orientation: A study by CSE that streets oriented along the north-south axis have an LST higher by 1°C as compared to streets along the east-west axis. 
• This is because the streets in north-south orientation are more exposed to the strong east and west sun. 

• Blue /Green infrastructure: They regulate temperature and relative humidity, absorb and decompose pollutants, improve the overall air quality and offer shade among other benefits.
• Improve Urban morphology: Using better roof materials, reflective paints and green roofs.
• Urban form-based codes: Such codes can address the unique features of a city or even a neighbourhood. 
• Different urban forms could have different zoning regulations with contextual cooling solutions. 
• For instance, an old market could have tree-shaded walkways, a temple precinct could have cool roofs and a business district could have a high effective vegetation cover (EVC) (30 percent).
• Amend building by-laws and master plans: A 1°C fall in ambient temperature can lead to a 2 per cent reduction in the city’s power bill.