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Monday, July 04, 2022

Explained: How heatwave is sweeping across India, again

Though heatwave over large parts of north and central India is an annual phenomenon in May, the maximum temperatures in areas of Delhi and Jammu and Kashmir have been unusually high. Why have the temperatures been so high?

Written by Anjali Marar , Abhinaya Harigovind , Edited by Explained Desk | New Delhi, Pune |
Updated: May 17, 2022 11:14:03 am
Heatwave, maximum temperature, India weather, IMD weather forecast, India heatwave, Express explainedA man drinks water to quench his thirst on a hot summer day, at Hazratganj crossing in Lucknow, Friday. (PTI)

Severe heatwave conditions have been consistently reported over large parts of India since the beginning of the summer season in March. On Sunday, the mercury touched nearly 50 degrees Celsius in some areas of Delhi and Uttar Pradesh, a day after Jacobabad in neighbouring Pakistan had recorded 51 degree Celsius.

This year, March and April saw early and unprecedented heat across India. March was the warmest and April was the fourth-warmest in 122 years. Though heatwave over large parts of north and central India is an annual phenomenon in May, the maximum temperatures in areas of Delhi and Jammu and Kashmir have been unusually high.

Sweltering heat grips north and central India

Jammu and Kashmir, Punjab, Rajasthan, Haryana, Delhi, Chandigarh, Uttar Pradesh, Madhya Pradesh, Gujarat, Maharashtra and Telangana are some of the states that witnessed heatwave conditions. A severe heatwave is declared when the maximum temperature jumps over 6 degrees Celsius above normal.

On Sunday, these departures were notably high and ranged between 7 to 9 degrees Celsius above normal across north and central India regions.

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Banda in the Bundelkhand region of Uttar Pradesh recorded 49 degrees. But this locality is known for such high temperatures during summer. Likewise, such extreme temperatures are normal over Churu or Ganganagar in Rajasthan.

As for the national capital region (NCR), Mungeshpur, in northwest Delhi, recorded a maximum temperature of 49.2 degrees Celsius while Najafgarh, in southwest Delhi, recorded 49.1 degrees Celsius on Sunday. In fact, all weather observatories in Delhi recorded maximum temperatures above 45 degrees Celsius on Sunday. The maximum temperature recorded at the Safdarjung observatory was 45.6 degrees Celsius, the highest so far this month.

Similarly, many locations in Kashmir recorded day temperatures around 30 degrees, usually warm for the Union territory’s summer capital. Some of the warmest locations (in degrees Celsius) on Sunday in the UT were Mirpur (46) Jammu airport (45), Srinagar airport (33.5), Anantnag (33.4) and Kupwara (30.2).

Why have the temperatures been so high?

Urban areas like Delhi and Gurgaon recording day temperatures in the 45-49 degrees Celsius range is abnormal and was aggravated by contributions from other local weather, and anthropogenic and man-made factors.

Western disturbances, which bring rainfall and cloudy skies to northwest India and regulate temperatures at this time of the year, have been feeble and lacked sufficient moisture, keeping the temperature high. In the absence of cloud cover, temperatures can soar with the solar radiation, while dry westerly winds do not bring any moisture.

The India Meteorological Department (IMD) rainfall data since March shows that many states in north and central India have remained parched.

The rainfall departures between March and May 15 were — Gujarat (97 per cent), Punjab (90 per cent), Haryana (87 per cent), Himachal Pradesh (86 per cent), Delhi (83 per cent), Madhya Pradesh (82 per cent), Jammu and Kashmir (78 per cent), Rajasthan (77 per cent) and Uttar Pradesh (74 per cent).

Delhi too has recorded a rainfall deficit this summer. While March saw no rainfall at all against a normal of 15.9 mm for the month, April recorded only 0.3 mm, which was way short of the normal of 12.2 mm. So far in May, the Safdarjung weather station, which provides representative figures for the city, has recorded 1.4 mm of rainfall, against a normal of 9.8 mm for the month. Last May, the station recorded a high amount of 144.8 mm of rainfall and the highest maximum temperature for the month was 41.6 degrees Celsius, below the 45.6 degrees recorded so far this year.

Heatwaves not unusual for May

Heatwave season over India begins in March and peaks in May, especially over the core heatwave zone areas. This summer saw record temperatures during March and April but such warm days in May are normal.

The current heatwave spell, prevailing for a week, is spread across 11 states and UTs. While the geographical extent may be similar to the spell recorded between March 27 and April 12, the severity this time is manyfold higher.

The last spell saw a severe heatwave limited to some pockets of Rajasthan and eastern Uttar Pradesh, whereas the May spell has had similar conditions raging across all north and central India regions.

On Sunday, more than ten meteorological stations recorded maximum temperatures over 47 degrees Celsius, including Banda (49), Gurgaon (48), Churu (47.9), Ganganagar (47.6), Pilani (47.7), Khajuraho and Nowgong (47.4 each), Jhansi (47.6), Hissar (47.3) and Delhi ridge (47.2).

Heatwaves more frequent now

At the Safdarjung weather station, the all-time record for maximum temperature in May is 47.2 degrees Celsius on May 29, 1944. From 2009 to 2021, the highest maximum temperature in May has been 45 degrees or higher six times – in May of 2010, 2012, 2013, 2015, 2018 and 2020. In the past 13 years, the highest maximum temperature recorded in May was 46 degrees Celsius in 2020.

In a note issued at the end of April, when parts of India were facing a heatwave, the Secretary-General of the World Meteorological Organisation, Prof. Petteri Taalas, said, “It is premature to attribute the extreme heat in India and Pakistan solely to climate change. However, it is consistent with what we expect in a changing climate. Heatwaves are more frequent and more intense and starting earlier than in the past.”

An early, warmer start to the summer this year meant that heatwave conditions set in over Delhi-NCR from March onwards, and northwest India recorded its hottest March and April in 122 years.

The Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report last year also stated that extremes of hot weather and heatwaves have become more frequent and more intense since the 1950s. The report identified “human-induced climate change” as the “main driver” of these changes.

Intensity set to reduce courtesy western disturbance

From Monday, the heatwave distribution and intensity are set to reduce from most of the north and central India regions, except Kutch-Saurashtra. The maximum temperatures will fall by 2 to 4 degrees Celsius but remain above the 40-degrees mark which is normal for May, as per the forecast.

The marginal drop is due to a fresh western disturbance approaching northern India. However, the relief will be short-lived as heat conditions are set to return around May 20 over Rajasthan, Haryana, Delhi, Chandigarh, Punjab, parts of Jammu, Uttar Pradesh, Madhya Pradesh and Jharkhand.

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The maximum temperature in Delhi on Monday and Tuesday could be around 41 degrees Celsius, before it rises again to around 45 degrees Celsius on May 20, when the heatwave returns as per the forecast. Cloudy skies and the possibility of rainfall are on the forecast for May 21 and 22, and the maximum temperature could drop to around 40 degrees on May 22. For this week, the maximum temperature could remain at 40 degrees or above in the national capital region.

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