Urban Heat Island effect

• Urban Heat Island is a localized and temporary phenomena when certain pockets experience higher temperature than surrounding areas. The variations are mainly due to heat getting trapped in localities that resemble concrete jungles: Greener rural localities often record cooler temperatures than urban areas.

WHY IN NEWS?

• Around midnight India time on May 5, NASA's space thermometer ECOSTRESS captured an image covering 12,350 sq km northwest of Delhi and showing a stark difference in nighttime temperatures in urban and rural pockets.
• Red patches on the image delineated urban heat islands amid significantly cooler rural patches - with a temperature difference of around 20°C.

NASA’s Findings

• Night time temperatures in Delhi and several smaller villages were above 35°C, while the rural fields nearby had cooled to around 15°C.
• This data suggests that city dwellers are experiencing considerably higher temperatures than the average temperatures reported for their regions.

Factors contributing to the creation of “Urban Heat Island”

• Insufficient Greenery - Buildings and skyscrapers tend to neglect the need for planting trees and plants on their premises. The designers, architects, and engineers fail to realize the benefits of greenery that create shade and a cooling effect in the air.
• Dark and Dull Coloured Roofs - The amount of heat absorbed by such a roof tends to intensify the heat inside the building. It is one of the potential and serious causes of the urban heat island effect. On the contrary, light-colored roofs reflect the solar radiation and create a cooling sensation within the building interiors.
• Thermal Mass - Planning to establish and construct buildings in close proximity is another vital cause of the urban heat island effect. The wind is blocked, thus preventing the cooling effect due to convection. Besides it also prevents the pollutants from being dispersed. Buildings in urban areas accumulate a considerable amount of heat throughout the day from the solar power of the sun’s heat radiations. At night though the temperature cools down yet the buildings are slow in releasing the heat at the same pace the way they absorb the heat.
• Air Conditioning - The usage of air conditioning in urban areas is increasing at an exponential rate. While it reduces the temperature inside the buildings and creates a cooling effect, it releases heat into the outside environment.
• Improper air circulation - Narrow streets, gigantic skyscrapers and buildings, inadequate ventilation, and lack of appropriate spacing between the buildings are responsible for poor air circulation in the adjacent surroundings. This results in high surface and air temperatures leading to the urban heat island effect.

How Green Can Help?

• Transpiration is a natural way of heat regulation that involves roots absorbing water from soil, before processing and releasing it in the form of water vapor.
• As urban areas lack sufficient green cover, heat regulation is either absent or man-made. Also, cities with buildings constructed using glass and concrete, all dark-coloured materials, attract and absorb higher heat content.
• On May 15, Najafgarhand Mungeshpur in Delhi recorded maximum temperatures of 49.2°C, while Mayur Vihar (45.4°C). Lodhi Road (45.8°C), Palam (46.1°C), and Ayanagar(46.8°C) were cooler.

Way forward

• Increasing green cover is one way to cut heat load within urban areas.
• Other ways of heat mitigation include appropriate choice of construction material, promoting terrace and kitchen gardens, and painting the terrace spaces using light colours to reflect heat.

Exam Takeaway

• Urban Heat Effect

Mains Question

Q. The Urban Island Heat Effect has emerged as a challenge for urban planners, as it makes the city inhabitable. Critically analyze the problem and suggest ways to deal with it.