By Climatalk Desk
Have you been to New Delhi in summer and walked around Connaught Place? If you found the heat was too much to bear, do not blame it on global warming.
It is not just the blanket of carbon dioxide and other heat-trapping gases that warms up the city heart of New Delhi – but also tarred roads, vehicles, buildings and their air-conditioners. These add-on factors top up the local temperature by two to eight degrees, as studies have shown.
Scientists say the additional increase in temperature is due to the ‘urban heat island’ effect. That means the built-up city centre is warmer than its open, green surroundings, even at night. It is not only New Delhi, but crowded cities all over the world face this problem, including Kolkata and Bangalore.
An Indian Institute of Technology (IIT) Delhi study presented at the Seventh International Conference on Urban Climate, 29 June – 3 July 2009 in Yokohama, Japan, gave a clear picture of the heat island effect in and around New Delhi. It found that the capital city’s business hubs such as Connaught Place, Sitaram Bazar, and Bhikaji Cama Place were the top three heat islands. At the same time, the city’s green spaces such as Buddha Jayanti Park, Hauz Khas Park, and Sanjay Van were cooler than the rest of the city.
For the study, Prof Manju Mohan of the IIT Delhi Centre for Atmospheric Sciences and her collaborators analysed 30 spots in a grid of 16 cells of 8 x 8 km each in the National Capital Region. Prof B R Gurjar from the Civil Engineering Department of IIT Roorkee and two scientists from Meisei University in Tokyo also took part in the study. The initial data was collected in May 2008. Mohan is now planning more detailed follow-ups.
So how do the heat islands warm up a city? The chock-a-block building patterns common to many rapidly growing urban areas where land is scarce create what scientists refer to as a low ‘sky view factor’ – you just cannot see the sky anymore, and there is no escape route for the heat, which then gets trapped between buildings and held close to the ground. The problem is made worse by roads criss-crossing the city, which often feature black tar surfaces that absorb heat, keeping temperatures above normal levels even at night, when the air would naturally cool down. In addition, urban spaces are feeling the brunt of artificial heat being produced by air-conditioners, buses and cars. Busy traffic junctions, where vehicles stop with their engines on, intensify the problem.
Scientists worldwide are now thinking of ways to make cities cooler by using appropriate building material, reflective paint and green surfaces on and around built-up spaces. Apart from science-driven solutions, however, large-scale change appears possible only if the world’s urban citizens realise that rising temperatures in their midst are a matter of grave environmental concern. They have to start playing a more active role by reducing individual traffic and demanding more efficient public transportation systems and approaches to urban planning. That is the best way to stop neighbourhoods from morphing into giant ovens.