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IMD issues heat wave alerts for five states

Published: 20th Apr, 2023


The India Meteorological Department (IMD) on Sunday issued a heat wave warning for West Bengal, Bihar, and Andhra Pradesh over the next four to five days.

What is Heat wave?

  • Heat Wave is simply, a continuous spell of abnormally hot weather.
  • Heat wave need not be considered till maximum temperature of a station reaches at least 40º C for Plains and at least 30º C for Hilly regions.

India and Heatwave:

  • Criteria for declaring Heat Wave:Heat wave is considered if the maximum temperature of a station reaches at least 40 degree Celsius or more for Plains and at least 30 degree Celsius or more for Hilly regions.
  • Period of Heat Wave in India: Heat waves generally occur over plains of northwest India, Central, East & north Peninsular India during March to June.
  • Heat wave prone states: It covers Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Odisha, Madhya Pradesh, Rajasthan, and Gujarat, parts of Maharashtra & Karnataka, Andhra Pradesh and Telangana. Sometimes it occurs over Tamil Nadu & Kerala also.
  • Favourable conditions for Heat wave:
    • Transportation / Prevalence of hot dry air over a region
    • Absence of moisture in the upper atmosphere
    • The sky should be practically cloudless
    • Large amplitude anticyclonic flow over the area.

Different standards on heatwaves

Several countries have adopted their own standards on heatwaves:

  • United States: The US National Weather Service defines a heatwave as a spell of “abnormally and uncomfortably hot and unusually humid weather” over two days or more.
  • Denmark: A heatwave occurs when the mean of the highest recorded temperature measured over three consecutive days exceeds 28°C (82.4°F).
  • Australia: In Adelaide, Australia, a heatwave is defined as five straight days with temperatures at or above 35°C (95°F), or three consecutive days at or over 40°C (104°F).

Impacts on India

  • Health effects:  Hyperthermia, also known as heat stroke, becomes common during periods of sustained high temperature and humidity.
  • Mortality: Heatwaves have killed more than 17,000 people in 50 years in India, according to a research study by IMD scientists.
  • Crop losses: heat waves and excessive heating impacts the standing crops of the regions, as they are not immune to more heat at that time of the year.
  • Psychological and sociological effects: In addition to physical stress, excessive heat causes psychological stress, to a degree which affects performance, and is also associated with an increase in violent crime.
  • Increase in surface ozone: ozone pollutionin urban areas is especially concerning with increasing temperatures, raising heat-related mortality during heat waves. During heat waves in urban areas, ground level ozone pollution can be 20% higher than usual.
  • Lead to wild fires: If a heat wave occurs during a drought, which dries out vegetation, it can contribute to bushfires and wildfires.
  • Power outages: Heat waves often lead to electricity spikes due to increased air conditioning use, which can create power outages, exacerbating the problem.

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