Urban Heat Island (UHI)
An urban heat island occurs when a city experiences much warmer temperatures than nearby rural areas.
The difference in temperature between urban and less-developed rural areas has to do with how well the surfaces in each environment absorb and hold heat.
Concrete structures and tarmac roads retain heat which stays trapped inside this “urban bubble” along with air pollutants.
A lack of green spaces and waste heat from air conditioners and other machinery add to the UHI
Dangers of UHI
Humidity reduces the cooling effect of perspiration, leading to a person experiencing an elevated body temperature, debilitating heat stress, exhaustion, and even a potentially fatal heat stroke.
In India, a heatwave is officially declared in coastal areas when the maximum temperatures are over 37° C and 4.5° C above normal.
The effects could be much worse, even dangerous, when compared to inland, rural areas.
Existing measures
India has national, State and even some district-level Heat Action Plans (HAP) to reduce morbidity and mortality, especially among the vulnerable poor, infants and the elderly.
The National Disaster Management Authority (NDMA) Guidelines, which are being upgraded, and those of several States, outline measures to deal with heatwaves including early warning bulletins, and staggered work hours at outdoor construction sites, with shaded areas and temporary shelters, and strategic provisioning of drinking water and oral rehydration salts.
Besides such post facto responses to heatwaves, longer term measures are needed to deal with UHI and reduce urban heat.
Solutions
Green areas such as urban forests, large greens and parks, avenue and other trees, even lawns, release moisture which evaporates and cools the environs.
Well-distributed green areas also influence local micro-climate, reduce air pollution, and promote health and well being
The more the UHI, the greater the use of air-conditioning, generating even more heat in a nasty feedback loop
If buildings are better insulated and ventilated, and constructed using appropriate designs and materials according to “green” building codes, they would require less air-conditioning and generate less waste heat
Having permeable pavings and walkways using alternative materials, increased shrubbery along sidewalks, berms and dividers, and reflective paint on roofs, walls and streets, are other measures to reduce UHI.
A sharp reduction in personal vehicles (most four-wheelers have powerful engines and air conditioners), through a rapid scaling-up of effective public transport with electric buses, would be another major contribution.
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