Ans. A heatwave is defined as a period of abnormally high temperatures in a specific region. The threshold for declaring a heatwave varies based on the region’s climatic norms. In India, heatwaves typically occur between March and June, though in rare cases, they may extend into July. Extreme temperatures create physiological stress, leading to severe health impacts, including mortality. Understanding the criteria for heatwave classification and its regional variations is crucial for devising effective mitigation strategies.

How is a Heatwave Declared?

The India Meteorological Department (IMD) has set specific criteria to declare a heatwave:

A heatwave is declared when the maximum temperature reaches 40°C or more in the plains and 30°C or more in hilly regions.
A heatwave is announced when the temperature deviation from normal is between 4.5°C and 6.4°C.
A severe heatwave is declared when the temperature deviation exceeds 6.4°C.
If the maximum temperature exceeds 45°C, a heatwave is automatically declared. A severe heatwave is declared if the temperature exceeds 47°C.
In coastal regions, a heatwave is declared when the temperature deviation is 4.5°C or more from normal and the actual temperature surpasses 37°C.
For a heatwave declaration, these conditions must be met in at least two stations within a meteorological sub-division for two consecutive days. The heatwave is officially declared on the second day.

Regional Variations in Heatwave Criteria

India's diverse geography results in varying heatwave conditions:

Northern Plains and Central India (e.g., Rajasthan, Uttar Pradesh, Madhya Pradesh): Frequent heatwaves with temperatures exceeding 45°C due to arid and semi-arid climate.
Eastern India (e.g., Odisha, Jharkhand, West Bengal): High humidity compounds the heatwave impact, causing greater thermal discomfort.
Western India (e.g., Gujarat, Maharashtra): Experiences dry heatwaves, with some coastal influence moderating extreme temperature spikes.
Southern Peninsula (e.g., Andhra Pradesh, Telangana, Tamil Nadu): Heatwaves occur with high humidity, leading to heat stress-related illnesses despite relatively lower temperatures.
Hilly regions (e.g., Himachal Pradesh, Uttarakhand, Northeast India): Even 30°C can be considered a heatwave due to the lower normal temperature range.

Implications for Public Health and Safety

The variations in heatwave intensity across India have significant implications:

Increased Heat Stress: High temperatures combined with humidity worsen discomfort, leading to dehydration, heat exhaustion, and heatstroke.
Night-time Temperature Challenges: When night temperatures remain high, the body cannot recover from daytime heat, increasing health risks.
Heat Cramps and Heat Strokes: Prolonged exposure can cause heat cramps (painful muscle contractions) and heat strokes (life-threatening condition with high body temperature and organ failure).
Heat Exhaustion Symptoms: Individuals may experience fatigue, dizziness, weakness, headache, nausea, vomiting, and excessive sweating.

Large parts of India continue to experience heatwaves, with no immediate relief in sight. The IMD has forecast heatwave conditions in regions such as Odisha, Jharkhand, Gangetic West Bengal, interior Odisha, Rajasthan, and North Gujarat. Given the increasing frequency and intensity of heatwaves due to climate change, adaptive measures such as heat action plans, public awareness campaigns, and infrastructure resilience are essential to mitigate their adverse effects on public health and safety.

Useful Links

Quick Links