SUBJECT :Climate 

The 'urban heat island effect' is more widespread in the island city as it is more densely built and does not have a national park or adequate wetlands to bring down temperatures, says a recent study.

The "urban heat island (UHI) effect" refers to the way in which cities become warmer than surrounding rural areas as temperatures are raised by heat-absorbing concrete and asphalt, high population densities, and pollution. The same factors make some urban neighborhoods warmer than others. The study, by Aparna Dwivedi, M V Khire and B K Mohan from IIT-Bombay's Centre for Studies in Resources Engineering, says Mumbai's proximity to the sea and exploding urbanization make it highly vulnerable to disasters of climate change.

"Land use guidelines need to be put in place and may also specify the use of materials which bring sustainable development and less UHI effect to Mumbai," the authors write in their study. In recent years, studies have found that pollution and the heat island effect may be contributing to a link between urbanization and thunderstorms in cities, including in Mumbai.

This research, part of an ongoing project, has implications for the current debate over the city's new development plan. Allowing large increases in built-up areas in already dense areas could aggravate the heat island effect, unless planned properly, says Khire. "Some areas would become like an oven," he says.

Dwivedi, an architect and doctoral student working under the guidance of Khire, is studying the growth in heat islands in the city over the past 15 years. "The idea is to look at what factors, from building materials and green cover to pollution and energy use most affect temperatures, and come up with mitigation measures," she says. Dwivedi says the paved surface of the runways, as well as the heat-absorbing metal and asbestos shanty roofs in the surrounding slums, make the airport area a hot zone.

Some kinds of glass, for example, emit more heat than others. And glass buildings require air-conditioning, which emits its own heat and pollution, reinforcing the heat island effect, notes Khire. Thermal imagery from May shows glass-curtain buildings in Bandra Kurla Complex emitting surface temperatures of up to 56 degrees Celsius.

The IIT study looked at surface temperatures from satellite data. These are not always consonant with air temperatures, so the researchers plan to correlate surface temperatures with data from the weather department to get a more accurate heat map.

This is perhaps the first comprehensive research on heat islands in Mumbai. The phenomenon is well-studied in cities like New York which have also introduced mitigation policies including the promotion of terrace gardens and white-painted roofs to deflect heat. "But temperatures here are generally higher," says Dwivedi, "so the issue is even more important for us".

Source: June 5, 2015, The Times of India