URBAN HEAT ISLAND

Recently a picture captured by NASA showed that how nighttime temperature in Delhi and adjoining villages were above 35 degrees Celsius which is also peaking at about 39 degrees Celsius, while the rural field nearby had cooled to around 15 degrees Celsius. The phenomena of urban heat island are growing in capital mainly because of escape in green infrastructure.

It has been observed that cities and towns are getting warmer than the surrounding rural areas mainly due to loss of green cover, increasing concretization, increased use of cooling equipment and vehicular pollution.

WHAT IS URBAN HEAT ISLAND?

• Urban heat island is defined as the local and temporary phenomenon in which certain areas within a city are experiencing higher heat than their surrounding area.
• This rise of heat mainly happens due to buildings and houses in cities made up of concrete where the heat is trapped and not able to release easily.
• Urban heat island is basically induced due to trapped heat between establishments made up of concrete.
• The temperature variation can range between 3 to 5 degrees Celsius.

FACTOR FOR THE FORMATION OF URBAN HEAT ISLAND

• The material used for making roads, pavements and roofs are made up of asphalt(tar), concrete and bricks which are opaque, do not transmit light and have a higher heat capacity and thermal conductivity than the nearby rural areas which have more trees and open spaces.

• Unplanned urbanization, industrialization and changing land use land cover (LULC) have increased urban heat island.
• The cause of urban heat islands is global warming, but the other is that these heat islands are linked to micro-climatic changes, which occur when we start disrupting our landscapes.
• It also occurs with black or any dark colour material which has been used in the construction material.
• Increasing the activity of deforestation and destroying the green area is also one of the factors for urban heat island. This reduces evapotranspiration which is responsible for circulation of water from the pores of leaves to the surrounding air.

IMPACT OF URBAN HEAT ISLAND (UHI)

• UHI decreases the air quality in the city as the pollution created by automobiles and industries are trapped within the city.

• Severe increase in the day and night temperature which lead to the migration of animal and human being.
• The combination of high day and night temperatures is dangerous as it seriously impacts the blood circulation and other bodily functions of people and animals leading to heat cramps, sleeps deprivation and increased mortality rate.
• As the house becomes hot and unable to cool down by midnight it starts acting as a heat trap and in such a situation, the body gets heated and the person may die due to cardiac failure.
• According to health statistics, heatstroke has become the second leading cause of death due to heat waves.
• Due To UHI, the species like lizards and gecko that like warm temperature starts colonizing in the cities. Insects such as ants are also more abundant in cities than in rural, these are referred to as ectotherms.
• It also impacts the nearby waterbodies as warmer water from rooftops, pavements are transferred to drains and released into nearby lakes and rivers thus impacting water quality.

STEP TO REDUCE URBAN HEAT ISLAND

• Ahmedabad become the first city to came up with heat action plan in order to control the increasing temperature.
• Restoration of tree cover, forest cover, wetland and natural ecosystem will enhance the green cover area and the focus must be on increasing the green infrastructure that includes cool roofs or painting house roofs in a light colour to reflect heat and using the sustainable cooling mechanism.
• Industries which also act as the heat trap, need to minimize heat emissions through thermal innovation.
• Using light-coloured concrete (limestone aggregate along with asphalt) to make the road greyish or even pink in colour like in some places in the US to increase the albedo.
• Encouraging civilians to plant more trees and even nurture them, in their neighbourhood.