Urban Heat Island

What are urban heat islands?

An urban heat island occurs when a city experiences much warmer temperatures than nearby rural areas.
Why and How Does Urban Heat Island Happen?
• Grass, trees and other vegetation have a natural ability to cool the air through moisture evaporation. This process is a byproduct of photosynthesis.
• Vegetation also provides shade to the ground, helps to reflect UV rays back at the sky and simply doesn’t retain heat.
• When building a city, trees, grass, plants and shrubs are naturally cleared away to build roads, buildings, parking lots and stores.
• The new materials that take the place of the plants retain heat instead of reflecting or dispersing it. (Concrete alone can be up to 50 degrees warmer than the air temperature through this heat absorption.)
• The more areas that are absorbing heat, the more heat that will be let off over time.
• Think about how rocks around a campfire continue to let off heat long into the night. Temperatures rise in those areas until you have the Urban Heat Island effect.

Why Does the Urban Heat Island Effect Matter?

• With any kind of increase in temperature that has been trending over time, there’s always the environmental concern associated with it.
• If cities see higher and higher temperatures it can result in summer heat closures, worsening air quality, heat warnings and heat-related illnesses and death.
How can urban heat islands be reduced?
• The main way to cut heat load within urban areas is increasing the green cover; filling open spaces with trees and plants.
• Other ways of heat mitigation include appropriate choice of construction materials, promoting terrace and kitchen gardens, and painting white or light colours on terraces wherever possible to reflect heat.
What has NASA said on urban heat islands in India?

NASA recently pointed out heat islands in urban parts of Delhi, where temperatures were far higher than nearby agricultural lands.
NASA’s Ecosystem Spaceborne Thermal Radiometer Experiment (Ecostress) showed a large red patch around Delhi and smaller red patches around neighbouring cities of Sonipat, Panipat, Jind and Bhiwani. These red patches, implying higher temperatures, were the heat islands
Q. What are urban heat islands? Why do they form ? Do they play a part in aggravating heat wave conditions? Examine. Mention ways to reduce urban heat island effect.