Severe Heatwave in India

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What’s in today’s article?

  • Why in the News?
  • What is Heat wave?
  • What is Criterion for Declaring Heat wave?
  • How India Meteorological Department (IMD) Monitors the Heat wave?
  • How Does Heatwave Affect Human Body?
  • How to Avoid Heat Stroke?
  • News Summary
  • Why Has April Month Been so Hot?

Why in the News?

  • India continues to battle temperatures soaring to record levels, especially in April.
  • The month has brought unusually intense heat, affecting even hill stations and other regions not usually associated with the weather.
  • The southern peninsular and southeastern coast regions, which include Maharashtra, West Bengal, Telangana, and Andhra Pradesh, among others, have been worst affected.

What is Heat wave?

  • 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.
  • In certain countries it is defined in term of the heat index based on temperature and humidity or based on extreme percentile of the temperatures.

What is Criterion for Declaring Heat wave?

  • Heat wave is considered if maximum temperature of a station reaches at least 400C or more for Plains and at least 300C or more for Hilly regions.
  • For coastal regions –
    • When maximum temperature departure is 4.50C or more from normal, Heat Wave may be described provided actual maximum temperature is 370C or more.
  • Period of Heat wave over India –
    • It is occurring mainly during March to June and in some rare cases even in July. The peak month of the heat wave over India is May.
  • Heat wave prone areas of India –
    • Heat wave generally occurs over plains of northwest India, Central, East & north Peninsular India during March to June.

How India Meteorological Department (IMD) Monitors the Heat wave?

  • IMD has a big network of surface observatories covering entire country to measure various metrological parameters like Temperature, Relative humidity, pressure, wind speed & direction etc.
  • Based on daily maximum temperature station data, climatology of maximum temperature is prepared for the period 1981-2010 to find out normal maximum temperature of the day for particular station.
  • Thereafter, IMD declared heat wave over the region as per its definition.

How Does Heatwave Affect Human Body?

  • We all feel drained and tired after stepping out on an extremely hot day.
  • This is referred to as heat exhaustion, which happens when the body sweats excessively to keep the core temperature low.
  • A heat stroke happens when the ambient temperature is so high that the body is unable to sweat to regulate the core temperature, which shoots up to 400C.
  • In these cases, there is a severe imbalance of salts such as sodium and potassium in the body.
  • The high core temperature coupled with salt imbalances disrupts organs, leading to a host of symptoms.
  • It can affect the brain, making a person foggy, drowsy, and in severe cases may also lead to a person going into a coma.
  • It can lead to kidney and liver damage as well. A cascade of such symptoms leads to death due to heat stroke.

How to Avoid Heat Stroke?

  • The primary aim should be to bring down the core temperature of the body fast.
  • This can be done by pouring cold water over the person, making them drink cold drinks, and giving them electrolytes to balance salt levels.
  • To prevent heat stroke, it is better to avoid stepping out in direct sunlight, especially between noon and 3 pm. You should avoid strenuous activity during this time.

News Summary

April Heatwave
  • According to The Indian Express, the Core Heatwave Zone (CHZ) spanning central, north, and peninsular India is prone to heatwave annually, between March and June.
  • Rajasthan, Punjab, Haryana, Chandigarh, Delhi, West Madhya Pradesh, Uttar Pradesh, Chhattisgarh, Odisha, Vidarbha in Maharashtra, parts of Gangetic West Bengal, coastal Andhra Pradesh, and Telangana are the most heatwave-prone states or regions, the report explains.
  • However, this month, large areas of Karnataka, Kerala, Sikkim, Bihar, and Jharkhand also felt the heat, indicating that the temperatures are rapidly soaring during summers.

Why Has April Month Been so Hot?

  • In its forecast for April, the IMD warned of extreme heat and prolonged heatwave conditions to prevail over large parts of the country during the month. There are two main reasons for this.
  • One, 2024 is a year that began in an El Niño state.
    • El Niño, a weather pattern, refers to an abnormal warming of surface waters in the equatorial Pacific Ocean, which leads to extreme heat in many parts of the world and the ocean.
    • It developed in June 2023 and generally, the years which begin in an El Niño state, experience extreme temperatures, harsh, multiple and extended heatwave spells, and lack of pre-monsoon rainfall.
  • Two, the persistent presence of anticyclone systems over southern peninsular and south-eastern coastal areas.
    • These high-pressure systems, which exist at about the altitude of 3 km and extend between 1,000 and 2,000 km in length, push the air underneath them towards the Earth, in a process called air subsidence.
    • As a result, the forcefully sunk air generates more heat on the surface closer to the Earth.
    • The presence of anticyclone systems also leads to wind flow from land towards the sea and prevents the incoming cooler sea breeze, which is otherwise responsible for cooling land from time to time.
  • El Niño and anticyclone systems collectively created sweltering hot conditions and heatwaves during April, especially over Gangetic West Bengal, Odisha, Andhra Pradesh, Telangana, Tamil Nadu, Kerala, Karnataka, and Maharashtra.
  • The Intergovernmental Panel on Climate Change (IPCC) reports and analysis of weather models indicate that heatwaves in India shall no longer remain contained over only those regions traditionally believed to be prone.

Newer areas, especially from the southern peninsular India, are already experiencing heatwaves.


Q1. What is Loo?

The Loo is a strong, dusty, gusty, hot and dry summer wind from the west which blows over the Indo-Gangetic Plain region of North India and Pakistan. It is especially strong in the months of May and June. Due to its very high temperatures, exposure to it often leads to fatal heatstrokes.

Q2. What do you mean by La Nina?

La Nina is a cooling of the water in the equatorial Pacific, which occurs at irregular intervals, and is associated with widespread changes in weather patterns complementary to those of El Niño, but less extensive and damaging in their effects.

Source: Heatwaves in several parts of India: Why has April been hotter than usual? | ToI