The Indian Meteorological Department (IMD) issued a red alert for heatwaves in Delhi, Punjab, Haryana, and most parts of Western Rajasthan for Sunday (May 19). The agency also said that heatwaves and severe heatwave conditions will likely prevail here for five days beginning Sunday.
Delhi, Chandigarh and other major cities in these states have recently witnessed temperatures around and over 44°C. What exactly is a heatwave, which parts of India are most affected, what are severe and red heatwave alerts, and what precautions should be taken? We explain.
What is a heatwave alert and how is it issued?
According to the IMD’s website, “Qualitatively, heat wave is a condition of air temperature which becomes fatal to human body when exposed. Quantitatively, it is defined based on the temperature thresholds over a region in terms of actual temperature or its departure from normal.”
Therefore, for every region, a heatwave is determined based on the degree of difference from its usual temperatures. “Heat wave is considered if maximum temperature of a station reaches at least 40°C or more for Plains and at least 30°C or more for Hilly regions,” the IMD states. For coastal areas, it is when the maximum temperature departure is 37°C or more than normal.
Such temperatures must be recorded at least in two stations in a meteorological sub-division for at least two consecutive days. The heatwave is declared on the second day.
And what is a severe heatwave?
If the prevalent temperature is 4.5°C to 6.4°C more than normal, it is classified as a heatwave. A rise of more than 6.4°C is considered a severe heatwave. May is the peak month for heatwaves in India.
Heatwaves cover Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Odisha, Madhya Pradesh, Rajasthan, Gujarat, parts of Maharashtra and Karnataka, Andhra Pradesh and Telangana. Sometimes they occur in Tamil Nadu and Kerala, too. Maximum temperatures above 45°C are observed mainly in Rajasthan and the Vidarbha region in May.
What is a heatwave red alert?
A red alert refers to an extreme heat warning. It means that a severe heatwave has persisted for more than two days or the total number of heat/severe heatwave days has been more than six days.
There is a “very high likelihood of developing heat illness and heat stroke in all ages,” according to IMD. Extreme care needs to be exercised for vulnerable people, such as the elderly, infants and those with chronic diseases. The Chandigarh administration is reportedly considering shutting down schools by noon, given these conditions.
Notably, a US-based group of climate scientists called ‘Climate Central’ said human-caused climate change has made this intense heat much more likely. According to the World Health Organization, more than 1,66,000 people died as a result of heatwaves between 1998 and 2017.
Here is what the full spectrum of heatwave alerts says:
Heatwave alerts based on colour. (Via IMD website)
What are the precautions for heatwaves?
According to the National Disaster Management Authority (NDMA), the following measures can be taken to minimise heatwave impact:
*Avoid going out in the Sun, especially between noon and 3 pm.
*If you work outside, use a hat or an umbrella and apply a damp cloth on your head, neck, face and limbs.
*Drink sufficient water as often as possible, even if not thirsty.
*Wear lightweight, light-coloured, loose, and porous cotton clothes. Wear protective goggles, an umbrella/hat, shoes or chappals while going in the Sun.
*Avoid alcohol, tea, coffee and carbonated soft drinks, which dehydrate the body. Drink ORS, homemade drinks like lassi, torani (rice water), lemon water, buttermilk, etc. instead.
How should a heatstroke be treated?
In case a person has been affected by sunstroke, this is what they should do:
*Lay the person in a cool place, under shade. Wipe them with a wet cloth/wash the body frequently. Pour normal-temperature water on the head. The main aim is to bring down the body temperature.
*Give the person ORS/lemon sharbat/torani or other liquids useful for hydrating the body.
*Take the person to the nearest health centre immediately. Medical attention is needed as heat strokes can be fatal.
Visitors at the Agra Fort on a hot summer day on Thursday, May 16, 2024. (PTI Photo) 
Heatwave alerts based on colour. (Via IMD website)
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