Since 1985, in the month of May, Delhi has witnessed temperatures over 46.4 degrees Celsius only four times. According to Met department records for Delhi airport, in the last 31 years, such high temperatures have been seen at IGI airport between May 28-31, 1988; May 23-29, 1998; and May 22-25, 2013.
During these heat spells, the highest ever temperatures for the month were recorded on May 26, 1998. That day 18 years ago, the temperature at Palam touched 48.4 degrees — the highest since May 1969-2015. However, Safdarjung recorded 46.5 degrees the same day. At Safdarjung observatory, where older records are available, the highest temperature recorded is 47.2 degrees on May 19, 1944.
According to Dr R K Jenamani, head of airport Met office, “Temperatures crossing 44-45 degrees in the month of May is not new for Delhi. But what is unique this year is that while these spikes are usually seen in the second half of May, this summer we saw these trends from the first week.” On May 2, about two weeks after temperatures showed initial spikes, Palam recorded 46.2 degrees and Safdarjung 44 degrees.
According to Met data, April 18 was the first high temperature day observed this summer. Safdarjung and Palam recorded temperatures of 42 and 44 degrees, respectively, that day. On May 2, the temperatures were 44 and 46.2 degrees at Safdarjung and Palam, respectively. Temperatures rose through May 13, 14 and 15 and hit the season’s highest of 46.4 degrees at Palam on May 18. Safdarjung recorded 43.7 degrees the same day. In Delhi airport, the Met office recorded 45 to 47 degrees on the runways consistently from 1.30 pm to 6.30 pm on May 18.
“We compared this with runway temperatures at other airports such as Jaipur, Lucknow and Udaipur. All major airports in north India reported the highest temperatures this season the same afternoon period, but it ranged from 42 to 45 degrees. So, Delhi airport saw the highest temperatures on the runway in this region so far this season on May 18,” said Jenamani. Temperatures hovered between 42 to 44 degrees till May 21.
According to Jenamani, the spike in temperatures in May has come after a gap. “In May 2015, such high temperatures were there for one to two days at both Palam and Safdarjung. In the preceding years, there was no prominent heat wave spell. In May 2013, when we last saw persistent heat, the conditions were most prominently observed during May 20-25, when temperatures at Palam were 46.3 to 47.2 degrees. At Safdarjung, the highest temperature for the month that year was seen on May 24 at 45.7 degrees.”
Such high temperatures are often followed by dust storms due to convection currents. This season, so far, such storms were only witnessed on May 16 evening, when wind speeds of 55 kmph between 7.20 and 7.50 pm reduced visibility from 6,000 metres to as low as 900 metres, while temperatures remained between 37 and 43 degrees.
The high temperatures seen in Delhi over the last week are between 3.1 to 5 degrees above normal for this time, according to the India Meteorological Department (IMD). Jammu and Kashmir, Rajasthan, and parts of Haryana all saw similar conditions, said the IMD. According to a senior scientist from IMD, “The temperatures in Delhi have fallen after crossing 45 degrees over the last week. High temperatures continue to persist in Rajasthan and Madhya Pradesh.” Some relief is expected after the advent of southwest monsoon and easterly winds, the scientist added.
The high temperatures also led to spike in ozone levels by 15 to 20 per cent, by modest estimates. According to Central Pollution Control Board’s Air Quality Index bulletin, between May 12 and May 18, when temperatures remained high, ozone was recorded as the dominant pollutant. “Ozone is formed as a photochemical reaction where different pollutants including dust and gaseous particles combine. High temperatures are an important catalyst, so the spike coincided with the rise in temperatures,” said a scientist.
On Sunday, maximum temperatures spiked by 1 to 2 degrees — Palam recorded 45.6 degrees and Safdarjung 43.7 degrees, according to the Met office — with the change in wind direction to westerly from easterly at 11.30 am. According to Jenamani, new winds from Rajasthan were responsible for the spike.
Hourly weather data of Delhi shows after May 18, temperatures did not rise due to the formation of a cyclone parallel to eastern coast of India. “These turned the winds in the easterly direction from May 19-20, bringing high humidity to the city… So, the eastern region of Delhi had relatively lower maximum temperatures in the last three to four days. Maximum temperatures fell by 2 to 3 degrees as a result of the moist winds,” said Jenamani. He added that due to the moisture in the winds, humidity increased. “It felt very uncomfortable even through temperatures fell by 2 to 3 degrees during May 20-22, compared to the much higher temperatures on May 18.
On May 22, the Met department said prevailing heat wave conditions are likely to subside from May 27. While maximum temperatures are “very likely” to fall by 1 to 2 degrees over Rajasthan, Madhya Pradesh and Gujarat due to incoming westerly disturbances, “no significant change” is expected over Punjab, Haryana, Chandigarh, Delhi and Uttar Pradesh during the next 48 hours.
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