Prolonged and intense heat waves in northwest India, with high day and night temperatures, cause heat stress and health emergencies.
This year’s arduous summer, which has led to oppressive conditions for millions of people across the country, has sparked what is perhaps the most prolonged spell of heat ever recorded in at least 50% of northwest India — Delhi, Punjab, Haryana, and Rajasthan — data shows.
This heat spell across India’s north, east and northwest is also particularly agonising due to the unusually extreme night-time temperatures, which India Meteorological Department (IMD) scientists call “warm nights”, being experienced across the swathe of areas in the grip of the heat streak.
Scientists and doctors said that combination of high day-time and night-time temperatures has led to conditions that put immense heat stress on the body, especially for those who are without access to air conditioners or coolers. It is further aggravated by the lack of availability of cool water.
In many areas in Delhi, for example, people are getting unusually warm tap water through day and night.
Data analysed by HT shows that more than half of northwestern India has experienced a maximum temperature of 40 degrees Celsius (°C) or higher on almost all days in the past 33 days (the period between May 16 and June 17). This makes it the longest 40°+ spell since 1951 in most parts of Delhi, Punjab, Haryana, and Rajasthan. Nearly half of Gujarat (around 44% of the state) and more than a third of Uttar Pradesh (34% of the state’s area) are also experiencing its worst heat spell since 1951, the earliest year for which data is available.
This also shows how wide a swathe is in the grips of this excruciatingly long heat spell.
In nearly a quarter of the country’s area (24%), this year is at least in the top five longest heat spells ever recorded. It is among the top 10 in 32% of the area, and among the top 20 in 40% of the country’s area. To be sure, this is the case when 37% of the country’s area has either never reached a 40°C reading in the May 16-June 17 period, or did not this year. If we exclude this area, then 40°C+ temperatures have been experienced on the maximum number of days this year in over 25% of India.
While the extreme day temperature is part of the problem, it does not fully capture why this year’s heat has felt agonising. For that, weather scientists, point to the high temperature that is also prevalent in the night — the only time people expect any relief.
“The day temperatures are way too high. So naturally the nights are not able to cool down as much. If the maximum temperatures are in the range of 45-46°C, you cannot expect night time temperatures to be normal either,” said M Mohapatra, IMD director general.
A warm night is declared only when the maximum temperature remains 40°C or more, and is defined based on departures of actual minimum temperatures. A warm night is when minimum temperature departure is 4.5°C to 6.4°C above normal.
“More warm nights are being experienced this time… At night there is an outgoing longwave radiation or the heat is radiated back. But the temperatures are so high and hot westerly winds are blowing at night, so that is not happening as expected,” said Mahesh Palawat, vice-president, climate and meteorology at Skymet Weather.
The monsoon, which has barely progressed beyond central India since June 11, has only added to the woes. “We are expecting monsoon to pick up in a few days which may help in modulating temperatures,” Palawat added.
The average June rainfall for the country as a whole is most likely to be below normal (< 92% of the Long Period Average (LPA), IMD said on Tuesday. LPA of the June rainfall over the country as a whole for the period 1971-2020 is 16.69cm. Normal to above normal monthly rainfall is most likely over most areas of the south peninsular India and some areas of Northeast India. Below normal rainfall is most likely over many areas of Northwest & adjoining Central India and some areas of Northeast India.
