Urban canyons trap heat
Urban canyons trap heat
PTI

If it feels like summer in mid-March, don’t blame global warming. It’s the usual suspect but the culprit here is not the natural environment as much as the man-made environment -- the concrete jungle -- which creates heat islands or localities that are substantially warmer than their surroundings.

In Mumbai, the surface temperatures during summer in crowded central suburbs such as Kurla and Andheri East, can be eight to nine degrees Centigrade higher than in other parts of the city. This is the finding of a study on the urban heat island effect in Mumbai by Aparna Dwivedi, M V Khire and B K Mohan at IIT-Mumbai’s Centre for Studies in Resources Engineering.

Giant reservoir of heat

Urban heat islands are not only hotter than surrounding areas in the day but also in the night. This is because the tightly packed concrete buildings, asphalt roads, paved compounds, not to forget the thousands of cars parked in the open, collectively form a giant reservoir of heat that drains out gradually after sunset.

Kurla and Andheri East not only lack open spaces and greenery but are also on the periphery of the airport with its massive paved surface of the runways, notes the IIT study. To make matters worse, the airport is surrounded by slums with tin and asbestos roofs.

Mumbai records lower temperatures on the peripheries and coast, but is “highly heated in the centre”, says the IIT-Mumbai study.

Urban heat islands

All studies on the urban heat island phenomenon in India say that such hotspots are increasing. In fact, the one by IIT-Kharagpur, which studied 44 major cities between 2001 and 2017, shows that most cities in India are turning into urban heat islands in all seasons, during day and night.

The Energy and Resources Institute (TERI), a research nonprofit organisation based in Delhi, found that temperatures in Delhi and Mumbai had risen by two degrees Centigrade in the last two decades. NASA satellite readings show Delhi and Mumbai to be five to seven degrees Centigrade warmer than the surrounding rural areas on summer nights.

The gap between the daytime maximum temperature and the nighttime maximum temperature in major cities has been declining over the years.

Our cities are turning into ovens. Expected, given the urban canyons which trap heat, millions of cars and air-conditioners pumping out heat and more hoardings than trees. In Mumbai, tall buildings along the coast block the sea breeze as well.

In denial

The urban heat island phenomenon has been studied extensively in the West and mitigation measures taken but we have been living in denial.

Look at our infatuation with glass façade buildings which Europe uses for trapping the scant sunlight. In the tropics, the same structure gets so hot that it takes a lot of electricity to cool it. A study by the Institute of Science, Bangalore, showed that glass buildings consume ten times as much power as the normal ones.

In fact, the IIT-Mumbai study found that glass-clad structures in the Bandra-Kurla Complex were emitting surface temperatures of up to 56 degrees Centigrade in peak summer.

Heat islands worsen heat wave conditions which lead to sleep deprivation, heat cramps and increased mortality rates. They also exacerbate haze formation, which causes respiratory disorders.

A lesser known fact is that the higher temperature in urban areas increases the colonisation of species that like warm temperatures, such as lizards and geckos. For the same reason, insects such as ants are more abundant here than in rural areas.

Cool norms

All the heat island studies stress that Indian cities need to introduce building codes that ensure inhabitants are protected from extreme temperatures.

Building bylaws should include passive ventilation but the reality is that our architects have forgotten cross-ventilation.

Cool roofs ought to become the norm. These are roofs designed to reflect more sunlight and absorb less heat than a standard roof through use of a highly reflective type of paint, a sheet covering, or highly reflective tiles or shingles.

Pertinently, the Taj Mahal and many Indian palaces used water channels running through the walls for cooling. This principle of radiant cooling is now being used in office complexes, such as the Infosys tower in Hyderabad.

Citizens should be encouraged to grow creepers and curtains of vegetation outside their windows, even kitchen gardens on the terrace. Instead, many housing societies in Mumbai have banned window gardens.

Greenbelts around cities, for wind paths, would allow the passage of exhaust heat from urban air conditioners and automobiles. However, every square inch of space is sought to be built upon. Mumbai plans commercial complexes in its vacant octroi posts.

Tree hackers

We have no qualms in hacking century-old landmark trees. We don’t even have a tree policy. Mumbai’s civic Tree Authority is packed with political appointees who can’t identify more than five trees.

In 2019, the Devendra Fadnavis government overnight cut down 2,141 fully-grown trees in Mumbai’s Aarey forest for a metro carshed, despite protests from citizens. The Aarey carshed was scrapped by the Uddhav Thackeray government.

According to a study led by the Indian Institute of Science, 94 per cent of Mumbai has been paved and concretised in the past four decades and in the process, it has lost 60 per cent of its vegetation and 65 per cent of its water bodies.

According to the Observer Research Foundation, Mumbai has an abysmal 1.24 sq m of accessible open space per person, ahead only of Chennai, which stands at 0.81 sq m per capita. The corresponding figure for Delhi is 21.52, while that for Bangalore is 17.32. London has 31.68 sq m, New York City has 26.4 sq m and Tokyo has 3.96 sq m of open space per capita.

Tandoori nights

On paper, India has a cooling action plan that recommends funding and support for initiatives such as cool-roof programmes, off-grid micro-systems for cooling and localised heat-action plans.

We don’t react till a catastrophe strikes. Ahmedabad implemented a heat action plan after a severe heat wave in 2010. It included a cool-roofs programme and simple measures, such as shifting maternity wards from the top floor to the ground floor, which brought down infant morbidity sharply.

Unless we take urban heat islands seriously, we will have to live with tandoori nights.

The writer is an independent journalist based in Mumbai.

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