New Delhi: Summers feel warmer in cities than the suburbs, sure, but by how much? Scientists at the Jamia Millia Islamia University in Delhi have completed a study showing that a significant 70% of the differences in temperature across Delhi can be explained by the varying density of population in the city’s boroughs.
While urban planners and climate scientists have long known about the so-called urban heat island effect, where cities in general are hotter than their surrounding rural areas, the Jamia scientists say their study is unique because it puts numbers to differences in temperature in Indian cities.
The study, by researchers Javed Mallick and Atiqur Rahman, shows that pockets of Delhi that had a population of 60,000 per sq. km were almost a degree hotter than those with a density of 20,000. Regions with about 85,000 denizens per sq. km were nearly 2.5 degrees warmer than those with only 10,000.
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“Most analyses of heat islands have been based on data from Europe and the US, so Indian studies should hopefully bring greater awareness to urban planners, when they design living spaces,” said Rahman.
With a population of approximately 17 million residents according to numbers from last year’s census, Delhi’s per sq. km density is 11,297 persons—the highest in the country. And the city’s north-east district has a density of 37,346 persons per sq. km, the highest for any borough in the country.
A new study uses census data and satellite imagery to study temperature differences between different parts of Delhi city.
For their analysis, Mallick and Rahman used the 2001 census data and temperature data from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), a Japanese sensor, which is one of five remote sensory devices on board the Terra satellite launched into Earth orbit by NASA in 1999.
In line with the distribution of population in Delhi, the researchers saw that the heavily built-up central Delhi was hotter than the not-so-heavily built-up sections in the north and south, and that the east, south-east and central parts of the city were the hottest. “These densely built-up areas are mainly because of increased economic activity and the fast development of residential societies to provide housing to the increasing population,” the authors said in their publication. “The increase in population density in turn leads to higher surface temperature in these particular areas.”
The only comparable Indian study on heat islands was published by researchers at the Centre for Ecological Sciences, at the Indian Institute of Science, Bangalore. The study showed that between the 1970s and 2009, urban Bangalore had grown nearly 600% and, just the last decade from 2000 to 2009, saw an average 2.5 degree rise in temperature.
P.K. Joshi, a professor at the department of natural resources in TERI University, said that heat island effects were accentuated by the kind of urban planning a city adopted. More buildings and wider roads trap heat and stimulate greater heating. “For instance, if two cities with the same population density used different construction materials, had better designs in their urban infrastructure, heating effects could be neutralized,” he said.
Graphic by Ahmed Raza Khan/Mint