In rare relief, no heatwave yet, none likely this summer: IMD

The Capital has not recorded a single heatwave day this summer. And with the forecast of another spell of rain at the end of next week, it is unlikely that Delhi will record any day of extreme heat this summer – a phenomenon experts said has never happened before in the city.

Weather scientists said that two cyclonic storms, along with a series of western disturbances through April to June were the primary reasons behind this year’s mellow summer in Delhi, a city known for its scorching heat this time of the year.

Between March 1 and June 3, Delhi has not recorded a single “heatwave” day, which India Meteorological Department (IMD) scientists said is a “rare” phenomenon for the city. IMD scientists also said that this could “very well be the first summer in Delhi’s history” that the city did not experience a single heatwave day.

HT reported last week that the Capital has been on a streak of weather records from August 2020. On June 1, the minimum temperature in the city dropped to 17.9 degrees Celsius, the lowest ever recorded in June.

In the plains, heatwave days are classified when two things happen – when the maximum temperature crosses 40 degrees Celsius, and when the day temperature exceeds the region’s normal maximum temperature by 4.5 degrees Celsius. A severe heatwave is when there is a rise of 6.5 degrees Celsius or above from normal temperature.

RK Jenamani, senior scientist at IMD, said a combination of conditions favourable for a cool summer have been seen in Delhi, which has resulted in no heatwave days. “We have not seen such conditions ever... This time of year is known for its scorching heat and high temperature. There have been years when the maximum temperature in May has even touched 48 degrees Celsius. We will have to wait till the end of June to declare if we have broken an all-time record of the coolest summer,” Jenamani said.

In Delhi, heatwave days occur between March and June, with April and May generally being the hottest. Towards the middle of June, the heat starts to abate with the onset of pre-monsoon and monsoon rains.

This year brings much-needed relief from the extreme heat in recent years. Last year, Delhi reeled under a severe heatwave spell from May 22 to May 30, with temperatures up to 47 degrees Celsius. Delhi recorded six heatwave days in 2019 and three such days in 2018.

Kuldeep Srivastava, head of IMD’s regional weather forecasting centre, said under the impact of cyclone Tauktae, Delhi broke the record for the highest single-day rainfall for the month ever on May 19-20, with 119.3mm of rain. This kept mercury low through May, with day temperatures dropping to 23.8 degrees Celsius on May 19, the lowest ever recorded in the month.

“Even after the cyclone’s impact, we got a consistent series of fresh western disturbances that passed over Delhi, which led to smaller spells of rainfall over the region. This helped keep mercury levels from rising,” Srivastava said.

He said that after Tauktae, Delhi also witnessed several days of cloudy skies due to cyclone Yaas. “Most of your extreme recordings are seen till June 15, because after that Delhi starts witnessing pre-monsoon activities, because of which temperatures start going down. So it is quite likely that we will not record any heatwave days this year,” Srivastava said.

IMD records show that Delhi’s Safdarjung observatory recorded zero heatwave days in 2014 and 2011. However, other weather stations in the city recorded heatwave conditions in both years. Srivastava’s claims were also confirmed by IMD’s latest forecast of fresh western disturbance passing over the region on June 11 and June 12, which is likely to bring rainfall by the end of next week.

Experts said that heatwaves are common in Delhi during this time of year as the region comes under the country’s core heatwave zone (CHZ), as categorised by IMD. Rajasthan, Punjab, Haryana, Chandigarh, Delhi, West Madhya Pradesh, Uttar Pradesh, Chhattisgarh, Orissa, Vidarbha in Maharashtra, parts of Gangetic West Bengal, Coastal Andhra Pradesh and Telangana come under CHZ, where high recordings are witnessed in summer. According to IMD, regions in CHZ experience at least six heatwave days every year.

Mahesh Palawat, vice-president, Skymet India Weather Services, however, said that while conditions indicate a below-normal summer season, it is too early to claim that temperatures will not rise as June progresses.

“It is true that heatwave conditions recorded in May are likely to last longer, compared to those reported in June because the intensity of heat often dies down sooner due to the onset of southwest monsoon. But there are years where we have seen extreme recordings (even in June),” Palawat said.

On June 10, 2019, Delhi’s Palam observatory recorded a maximum temperature of 48 degrees Celsius, breaking the previous all-time record of 47.8 degrees Celsius (June 9, 2014).