Climate Change and Extreme Heat: Calcutta and Bengaluru Face Rising Temperatures

June of a hundred years ago saw a temperature of 43.9°C in Calcutta. That happened very seldom. The capital of Bengaluru nearly broke its record in April of this year, with daytime highs of 43°C.

If climate scientists are correct, then if you think this summer is awful, be ready for the worst.

According to a research published in Springer in October 2023, the frequency of a daily maximum temperature above 43°C will tenfold rise over 25 years along India's east coast, which includes Calcutta. That will result in a 16-fold rise for the west coast and an additional seven-eight days on average in days with heatwave conditions.

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It is anticipated that this trend of more hot days will begin in 2025 and last for an additional 25 years. It won't give up. The number of heatwave days is expected to increase by 10–17 days between 2076 and 2100 compared to the current range, which, according to the India Meteorological Department, can last anywhere from one to five days during short– to medium–length periods between the months of March and June.

In the worst situation, that will last into July.

It is going to be a double-whammy for Calcutta because the city is experiencing increasing levels of heat and humidity discomfort, both of which are expected to continue rising.

Thus, even days with a lot of rain are not likely to bring about a lot of relief.

According to another study conducted by the Delhi-based environmental think-tank Centre for Science and Environment, the average heat index during the monsoon has already risen by 3.5°C from the pre-monsoon days in Calcutta, making the monsoons more miserable already.

The average heat index is a measurement of the perceived temperature after accounting for humidity in addition to air temperature. A 41°C heat index is deemed "dangerous for human health" by the US National Weather Service.

The CSE study examined Calcutta's heatscape from 2021 to 2023. Earlier this year, the report was released.

According to research, both dry and moist forms of heat stress have been impacted by climate change, according to Rajib Chattopadhyay, a scientist at the Indian Institute of Tropical Meteorology.

He claimed that "both dry and moist heat stress are on the rise." The effects of heatwaves on the human body are measured by heat stress. Our bodies need a steady internal temperature in order to function properly. A body under heat stress might not operate correctly.

When people with preexisting medical disorders are exposed to sunlight for longer than the threshold—which can vary from an hour to ninety minutes or more, depending on their unique circumstances—dry heat stress leads to dehydration and can have a serious effect on them.

According to Chattopadhyay, "moist heat stress arises when the body is unable to efficiently expel heat, and the surrounding humidity in the atmosphere exacerbates the discomfort." Excessive moisture prevents the body from sweating and prevents it from cooling off effectively. Internally, moist heat stress can be just as damaging as dry heat stress.

According to the CSE, there has been a 5.6 percent increase in heat stress in Calcutta between 2001–10 and 2014–23 due to a 5% increase in relative humidity.

The same analysis indicates that there has been an average 3.5% increase in the decadal heat index in Calcutta.

In addition, compared to 2001–10, the frequency of days with a daily heat index above 41°C has tripled.

The percentage of Calcutta's built-up area increased from 70.1% in 2001 to 80.1% in 2023 over the previous 20 years. According to the CSE, within the same time frame, the city's green cover decreased from 15.2% to 14.5% last year.

The model of Ahmedabad

In 2013, Ahmedabad became the first city in South Asia and India to have a heat response strategy. For those compelled to live in cement rooms with no ventilation and no access to a cooling system, the proposal recommended painting the tin roofs of the low-income housing complexes with heat-reflecting paint. It also includes clauses requiring all government, commercial, and municipal buildings to have cool roofs.

The May of 2010, when the heat is said to have killed over 1,000 people, swamped hospitals with heatstroke patients, and killed a few hundred bats, served as a wake-up call for the city authorities of Ahmedabad. Delhi has also had bat deaths this summer.

Heat advisories in Ahmedabad are disseminated by press releases, billboard announcements, and SMS and WhatsApp. To get the word out to the general public, radio hosts, health professionals, and community leaders are involved.

The heat action plan of Calcutta

As part of the heat action plan, the disaster management department of Bengal has created a list of dos and don'ts. The municipal government of Calcutta is developing a thorough climate action strategy specifically for the city.

"A few modifications have already been implemented," stated Debashish Kumar, a state lawmaker and member of the Calcutta Municipal Corporation's mayor-in-council. "To lessen the frequency of uprooting trees, changes have been made to the way walkways are paved and trees are pruned. Any pruning that upsets a fully established tree's equilibrium will be prosecuted, as will paving a walkway over exposed roots."

Heatwaves could sometimes occur earlier.

Based on a study published in Nature last month, India now has a 10% risk of experiencing an intense heatwave in late spring. In 2022, for instance, India experienced a heatwave in March.

India is concerned about the frequency, duration, and intensity of heatwaves brought on by anthropogenic climate change. It is necessary to execute an efficient heat plan action, according to Chattopadhyay.