A heat wave refers to an extended period of unusually high surface temperatures compared to the normal expectations. According to the World Meteorological Organization, it is defined as a period of five or more consecutive days when the daily maximum temperature exceeds the average maximum temperature by 5°C or more.

A report by the United Nations has warned that if global warming reaches 2 °C, a quarter of the world’s population could experience severe heat waves at least once every five years.

Phenomenon of heat waves:

  • During the summer in the Northern Hemisphere, the tilt of the Earth toward the sun leads to increased daylight hours in the northern half of the planet. This prolonged exposure to solar radiation accumulates over time, causing temperatures to peak several weeks after the longest day of the year.
  • Heat waves are initiated by the presence of a high-pressure system, also known as an anticyclone, which builds up atmospheric pressure over an area. This creates a descending column of air that compresses, heats up, and often dries out.
  • The descending air acts as a cap or heat dome, trapping the heat already absorbed by the surrounding landscape. This phenomenon prevents the warm ground air from rising and keeps it trapped near the surface. The absence of rising air encourages clear skies and a lack of precipitation, resulting in dry conditions. The incoming solar radiation further intensifies the heating of the ground.
  • The high-pressure system displaces cooler, fast-moving air currents and disperses clouds, allowing the sun to directly heat the ground without any obstructions.
  • As a result, the ground, including soil, sand, concrete, and asphalt, absorbs and radiates heat, leading to rapid temperature accumulation and compounding effects due to the long days and short nights of summer.

India, being a tropical country, experiences various heat wave conditions due to its unique geographical and climatic characteristics. The favorable conditions for the occurrence of heat waves in India include:

  • Presence of hot dry air over a region: A region with warm and dry air and suitable atmospheric flow patterns that transport hot air over the area.
  • Lack of moisture in the upper atmosphere: The absence of moisture allows for an unrestricted increase in temperature, making it conducive for the development of heat waves.
  • Clear sky: The sky should be mostly cloudless to allow maximum insulation over the region.
  • Anti-cyclonic flow: Heat wave formation is facilitated by the presence of a large-scale anti-cyclonic flow over the area.

Health impacts of heat waves:Rising temperatures pose a significant threat to human life, ecosystems, and the economy. Heat can worsen drought conditions, and hot and dry weather can increase the risk of wildfires. Heat waves have adverse effects on both humans and animals.

  • Health impacts of heat waves include dehydration, heat cramps, heat exhaustion, and heat stroke.
  • High temperatures are associated with an increased risk of heat-related illnesses, including cardiovascular and respiratory complications, kidney diseases, particularly affecting vulnerable populations such as outdoor workers, children, the elderly, and low-income households.
  • Extreme temperatures also affect air quality. Hot and sunny days can elevate ozone levels and nitrogen oxide levels, posing serious health risks to people.


Due to global warming, heat waves have become more frequent, severe, catastrophic, and unprecedented. Recent events like the historic California heat wave in June 2021 and the Indian heat wave in 2015 (which claimed more than 2,500 lives) highlight the urgency of collective efforts from the government, society, and civil society. Implementing advanced and accurate heat wave ranking systems and adopting multi-faceted climate change mitigation strategies are crucial steps needed to effectively address this disaster.

Legacy Editor Changed status to publish January 10, 2024