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India has witnessed a significant decline in heat-related deaths in recent years, reflecting the country's efforts to combat the adverse effects of heatwaves.

The India Meteorological Department (IMD) plays a vital role in this endeavor, issuing timely forecasts and warnings to mitigate the impact of severe weather events, including heatwaves.

Recently, IMD introduced the Heat Index, a valuable tool that considers humidity's influence on temperatures.

Heat Waves

  • Heat waves are prolonged periods of excessively hot weather that can cause adverse impacts on human health, the environment, and the economy.
  • India, being a tropical country, is particularly vulnerable to heat waves, which have become more frequent and intense in recent years.
  • IMD Criteria for Declaring Heat Wave in India:
  • Heat wave is considered if the maximum temperature of a station reaches at least 40°C or more for Plains and at least 30°C or more for Hilly regions.

Based on Departure from Normal:

Heat Wave: Departure from normal is 4.5°C to 6.4°C.

Severe Heat Wave: Departure from normal is >6.4°C.

Based on Actual Maximum Temperature:

Heat Wave: When actual maximum temperature ≥ 45°C.

Severe Heat Wave: When actual maximum temperature ≥47°C.

IMD's Initiatives and Tools to Combat Heat Waves:

  • Timely issuance of heat wave forecasts to keep the public informed.
  • Warnings provided to disaster management authorities for necessary preparedness.
  • IMD offers Seasonal outlook and extended range forecast offering additional insights into temperature trends.
  • Daily forecasts for the next five days with real-time updates.
  • Color-coded warnings for severe weather events, including heat waves.
  • Cooperation with National Disaster Management Authority (NDMA) and local health departments for heat action plans.
  • Implementation of plans in vulnerable regions to minimize heat-related risks.


  • The Heat Index is a parameter that considers both temperature and humidity to calculate the apparent temperature or "feel like" temperature for human beings.
  • It helps in understanding the impact of humidity on high temperatures and how it contributes to human discomfort during hot weather.
  • The Heat Index has been launched on an experimental basis by the India Meteorological Department (IMD).
  • It aims to provide general guidance for regions experiencing higher apparent temperatures causing discomfort to people.

Indication of Heat Stress:

High Heat Index values indicate a greater risk of heat-related stress and health issues.

It serves as a warning for potential heat-related illnesses and dangers.

Categorization of Heat Levels:

The Heat Index categorizes the apparent temperature into different levels using color codes:

  • Green: Experimental heat Index less than 35°C.
  • Yellow: Experimental heat Index in the range 36-45°C.
  • Orange: Experimental heat Index in the range 46-55°C.
  • Red: Experimental heat Index greater than 55°C.

Useful Tool for Public Health:

  • By understanding the Heat Index, individuals and communities can take proactive steps to protect public health during heatwaves.
  • It assists in making informed decisions and formulating heat action plans to ensure the well-being of the population.