These numbers were more than double of what these regions normally experience annually.
And, heatwaves continue to scorch many of these regions. Delhi, for instance, has seen three more heatwave days since June 9, including Thursday, taking the total so far to 23. IMD on Thursday said “severe heat wave conditions” over northern parts of India are likely to continue in the next 4-5 days.
Heatwaves are spells of unusually high temperatures as compared to what is normally expected over a region. Therefore, temperatures at which heatwaves are declared differ from place to place based on the historical temperatures of that region.
Data shared by IMD for the March 1-June 9 shows that 14 of 36 meteorological subdivisions in the country have recorded over 15 heatwave days. These subdivisions are spread across the country with east and north India the worst hit. Even the relatively cool high-altitude regions such as Himachal Pradesh reported 12 heat wave days followed by Sikkim (11), Jammu & Kashmir (6) and Uttarakhand (2).
“The IMD’s map shows a high number of heatwaves over India. This was expected and predicted in advance. In the year following an El Nino year (2023) we tend to get more heatwaves. That is due to favourable atmospheric circulation for heat waves,” said Madhavan Rajeevan, climate scientist and former secretary, ministry of earth sciences.
He attributed the longer spell to global warming, saying it is adding to the natural variability. “We will tend to get more frequent, longer and stronger heatwaves. We, therefore, need to be well prepared,” said Rajeevan while flagging the current longer spell against the normal 6-8 heatwave days averaged over central and northwest India per year.
A heatwave is declared when the maximum temperature of a weather station is at least 40 degrees Celsius in the plains and at least 30 degrees C in hilly regions, and it is 4.5 to 6.4 degrees C above the normal temperature. If it’s 6.5 degrees or more above normal, a severe heatwave is declared. Also, heatwave is automatically considered if the temperature touches 45 degrees C and a severe heatwave declared if it reaches 47 degrees C.
In the coastal area, a heatwave is declared if the maximum temperature is 37 degrees C or more and the departure is 4.5 degrees or more above normal.
The criteria of declaring heatwaves is, however, not the same in the other countries as quantitatively, there are different thresholds used around the globe. “It is usually defined based on the temperature thresholds over a region in terms of actual temperature or its departure from normal. In certain countries, it is defined in terms of the heat index based on temperature and humidity, or based on the extreme percentile of the temperatures,” the met department said.
“Heatwave to severe heatwave conditions are very likely to continue over Punjab, Haryana-Chandigarh-Delhi and Uttar Pradesh during next five days (till June 18) with a reduction thereafter in terms of areas and intensity,” said the met department in its extended range forecast for next two weeks.
