BENGALURU: After a week of evening showers early May, the weather has regained sizzle in Bengaluru, with Indian Meteorological Department pegging the average temperature for May - based on figures from 1990 to 2020 - at 33.1 degrees Celsius. The maximum temperature is between 33 and 35 degrees this week, but the weatherman says a two-degree deviation is not abnormal.
The merciless weather is a result of vegetation loss, urban heat island effect and unsustainable urbanisation. MN Thimmegowda, who heads agricultural meteorology at Gandhi Krishi Vigyan Kendra, said, "Tree cover and biodiversity are decreasing by the year. Due to cutting of trees, the heat that used to be trapped by the plant system is reaching us directly. Buildings dominate the landscape, and they warm up faster and re-radiate heat. Walls in the house feel warmer than the air outside. Ditto with the tarred roads, which also trap a lot of heat."
The expert recalled that he used to walk 8km to school decades ago, but would never sweat.
The thought of walking even 500 metres feels difficult due to the weather," he said, adding even when temperatures touched the 35-degree mark some years ago, they never felt the heat as they do now.
Jagdish Krishnaswamy, dean of environment and sustainability at Indian Institute of Human Settlement, said cities suffer from urban heat island effect due to massive concretisation. "This acts as a double blow along with effects of global warming," he said. The expert said 'wet-bulb temperature' of 35 degrees C is almost intolerable for humans, and high discomfort can be felt at wet-bulb temperatures above 32 degrees C.
Why no rain now?Datasets from the past decade show when Bengaluru crossed 34 degrees C, it would rain. "In the past 5-6 years, even if the temperature goes up to 35-36 degrees C, we are not likely to experience that kind of rain. This is due to distribution of rainfall being regulated by atmospheric pressure that depends on water transpired by plant system. When vegetation has declined, transpiration is less and the vapour-pressure gradient is not created to bring rain. That's why we don't get rain," said Thimmegowda, head of agricultural meteorology, Gandhi Krishi Vigyan Kendra.
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