The Telegraph
Wednesday , May 14 , 2014
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Exit poll heat, enter heatwave

Celsius falls but torment rises

After the heat and dust of elections, a heatwave hat-trick.

As south Bengal reeled under a record third heatwave of the season on Tuesday, Calcutta turned into a cauldron despite the Celsius dropping three degrees overnight from a decade high of 41.4 the previous day.

The Alipore weather office predicted that the maximum temperature would inch back to 40 degrees Celsius on Wednesday and stay in the red zone for a minimum of three days. A heatwave is declared when the maximum temperature fulfils the twin conditions of 40 degrees Celsius and five or more notches above normal.

“So many phases of heatwave are unusual. We can’t recall anything like this happening in at least the past 10 years,” said Gokul Chandra Debnath, director of the India Meteorological Department, Calcutta.

Most places in Gangetic Bengal recorded a maximum temperature in the range of 41 to 43 degrees Celsius. Calcutta’s 38.4 degrees Celsius had more to do with the partial cloud cover than any significant difference in conditions from the rest of south Bengal, weather scientists said.

The day’s maximum was still three degrees above normal and humidity negated whatever relief the temperature drop could have brought.

Minimum relative humidity, which indicates the moisture content in the air in the afternoon, more than doubled to 42 per cent from 18 per cent on Monday. So Tuesday was even more uncomfortable at 38.4 degrees Celsius than Calcuttans would have felt with the Celsius touching 41.4, but with lower humidity.

“Perspiration is the body’s mechanism of cooling down. But sweat takes more time to evaporate when relative humidity or moisture saturation in the air is more. When relative humidity is 100 per cent, sweat won’t evaporate at all. Since the minimum RH was close to 50 per cent on Tuesday, you would have felt more discomfort than during the previous day,” said a former professor of geography at Presidency University. “Laundry takes longer to dry in monsoon because relative humidity is high. It’s the same principle.”

Many thoroughfares in the city wore a deserted look in the afternoon. Those who stepped out had a hard time shielding themselves from the twin attack of heat and humidity. “Hot air kept coming out of my car’s AC for 10 minutes because I had parked the vehicle in the open for some time,” said Shomak Roychowdhury from Ballygunge.

At the Royal Calcutta Golf Club, fewer people turned up on Tuesday. Those who did were forced to pack up for the day by 9am. “Today, it was about 30-35 per cent less (the number of golfers). We are ensuring those on the course have plenty of water and fresh lime to drink,” said M.M. Singh, CEO of the club.

Gaurav Ghosh, general committee member of the RCGC, was one of the regulars who decided against teeing off after morning showed the day. “Today was excruciating, so I did not venture out. Tomorrow? Let’s see,” he said.

The sultry weather pushed up the demand for power. Consumption peaked at 1,957MW, an all-time record for the CESC-served areas in the city and Howrah. The previous record, also set this summer, was 1,921MW on April 29.

“During oppressive spells of heat, peak demand has been 100-150MW higher. We have been trying our best to cope with it and so far there have been no power cuts in the city except for a few local faults,” a CESC official said.

Weather scientists said the heatwave expected over the next few days would be different in character from the five-day heatwave in April.

“The local dry conditions were responsible for the last heatwave in April. The city will start getting dry winds from Bihar and Jharkhand on Wednesday afternoon,” the director of IMD, Calcutta, said.

The impact of the trough of low pressure that had triggered a rise in humidity on Tuesday could lessen over the next 24 hours.