City’s 262 green spaces provide cooling effects 347 metres beyond their physical boundary
Green cover, even in the heart of a dense city, can serve as nature’s very own eco-friendly and effective air-conditioners. In Bengaluru, urban green spaces (UGS) are on an average 2.23 degree Celsius cooler than surrounding areas. Not only that, the average UGS provided local cooling effects 347 metres beyond its boundary.
These were some of the key findings of a recently published study conducted by a team from the Indian Institute of Management, Ahmedabad, and the Indian Institute of Technology, Gandhinagar.
The study, which focussed on Bengaluru, is touted to be one of the first to quantify the role of urban green spaces in localised surface temperature reduction for a large Indian city. Published earlier this year in Science Direct, it analyses the cooling effect for 262 UGS in Bengaluru.
The researchers used high-resolution Landsat and Google Earth data and integrated it with spatial statistical analysis to quantify the cooling effects provided by UGS beyond their boundaries.
“The findings of this study are important in the context of India’s Smart Cities Mission that has been criticised for an inadequate focus on urban greening,” said the authors, Arpit Shah, Amit Garg and Vimal Mishra.
Mr. Shah, a post-doctoral researcher at IIMA, told The Hindu that the study was conducted in 2017, but the findings would still apply today, especially given that like most cities, Bengaluru too has seen increased construction and reduced green spaces in recent times.
He explained that the criteria for choosing the UGS was for the space to be at least one acre in size and with canopy cover. They did not account for water bodies. The scope of the study included prime lung spaces in the city such as Cubbon Park and Lalbagh.
“The average temperature difference between a green space and its surroundings, for the 262 green spaces in the study area, increased with distance from the green space. Cooling effects were maximum near the green space and subsided with distance. The temperature of the average green space was 2.23 degree Celsius lower than the temperature at its inflection point, where the cooling effects of the UGS subsided. The median cooling extent of a UGS was 270 mt, and the average cooling extent was 347 mt, post which the cooling effects of the green space subsided,” the paper stated.
This, explained Mr. Shah, can be looked at with the example of local pharmacy shops. Just like how one benefits from a local shop rather than a concentration of such shops in one part of the city, urban planners need to think of green spaces to be available within 100-150 metres of residents.
This analogy also applies to the concept of compensatory afforestation, wherein agencies choosing to plant trees in a place much away from where deforestation took place has been the subject of criticism.
Distribution of greenery
Water bodies too have a similar impact as that of green spaces, offering localised cooling effect, he added. But the same principles apply for both: they need to be distributed in different parts of the city, even if it means on smaller patches. “If vacant spaces can be converted now into green spaces, one can see the long-term effects in a few years,” he pointed out.
“The study points to the need for conserving green spaces in rapidly growing cities in India. This is more critical when India’s urban population is expected to double in the next three decades. Potential solutions to urban cooling could include introducing green cover at different locations in cities to enhance local cooling effects. Our results indicate that small green spaces that are spatially dispersed across the city could be useful in providing cooling effects,” the study concludes.
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