The IPCC defines heatwave as “a period of abnormally hot weather, often defined with reference to a relative temperature threshold, lasting from two days to months.”

• Heat Wave Duration Index & World Meteorological Organization— A heat wave occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C (9 °F).
• Heatwaves typically occur between March and June, more frequently over the Indo-Gangetic plains, on average, 5-6 heat wave events occur every year over the northern parts of the country.
• Heat cramps: Edelman (Swelling) and syncope (Fainting) are generally accompanied by fever below 39 degrees Celsius.
• Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps, and sweating.
• Heat stroke: Body temperature is at 40°C or more along with delirium, seizures, or coma which is potentially fatal.
• Heat waves are more frequent over the Indo-Gangec plains of India. On average, 5-6 heat wave events occur every year over the northern parts of the country.

Nodal Ministry: Indian Meteorological Department (Ministry of Earth Sciences, MOES)

Types of HeatWaves:

1. Moderate Heatwave: A heatwave with temperatures exceeding the normal maximum by 3-5°C. Example: A moderate heatwave in Delhi with temperatures reaching 42°C (108°F) in May.
2. Severe Heatwave: More intense than moderate heat waves, with temperatures exceeding the normal maximum by over 5°C. Example: A severe heatwave in Rajasthan with temperatures soaring to 50°C (122°F) in June.
3. Sustained Heatwave: A prolonged period of high temperatures lasting for several days. Example: A sustained heatwave in Odisha lasting for a week with temperatures consistently above 40°C (104°F).
4. Heatwave with High Humidity: Occurs when high humidity levels make it feel even hotter. Example: A humid heatwave in Mumbai with temperatures in the high 30s°C (around 100°F) and high humidity levels.

Criteria to declare:

1. Heatwave: When the maximum temperature of a met-substation reaches at least 40°C (104°F) in the plains or 37 degrees or more in coastal area, 30°C (86°F) in hilly areas
2. Severe Heatwave: When the maximum temperature of a met substation reaches at least 45°C (113°F) in the plains or 30°C (86°F) in hilly regions.

Causes:

Heatwaves in India can be caused by various factors, including:

1. High Temperatures: India’s geographical location and topography make it susceptible to intense heat.
2. Seasonal Weather Patterns: The movement of weather systems, such as the Indian Ocean Dipole and El Niño, can influence temperature and precipitation patterns, contributing to heat waves.
3. Lack of Rainfall: Prolonged periods of low rainfall, or droughts, lead to soil moisture depletion and less evaporative cooling.
4. Urban Heat Island Effect: Urban areas with concrete and asphalt can absorb and retain heat, causing localized temperature increases. Rapid urbanization contributes to this effect.
5. Global Climate Change: Long-term changes in global climate patterns can result in more frequent and severe heat waves.
6. Wind Patterns: Changes in wind patterns can influence the movement of air masses, potentially trapping warm air and causing prolonged periods of extreme heat.
7. Monsoon Delay or Failure: The delay or failure of the monsoon contributes to heat waves.
8. Deforestation and Land Use Changes: Alterations in land cover, leading to higher temperatures.
9. Human Activities: Activities like industrial processes, transportation, and agriculture can release heat-trapping gases and pollutants, contributing to local warming.

Mitigation:

1. Early Warning Systems: Implement advanced meteorological forecasting systems to provide early warnings about impending heatwaves.
2. Cooling Centers: Establish cooling centers in urban areas where vulnerable populations can seek refuge during extreme heat events.
3. Urban Planning: Design and retrofit urban areas to reduce the urban heat island effect.
4. Building Design: Promote energy-efficient building designs that incorporate natural cooling techniques, such as proper ventilation, insulation, and shading.
5. Public Awareness: educate people about the risks of heatwaves and the importance of staying hydrated, wearing appropriate clothing, and avoiding outdoor activities during peak heat hours.
6. Water Supply: Ensure stable and reliable access to clean water as it is crucial for hydration and cooling.
7. Healthcare Preparedness: Train healthcare workers to recognize and treat heat-related illnesses promptly.
8. Heat-Related Research: Invest in research to better understand local climate patterns, heatwave dynamics, and vulnerability assessments to tailor mitigation efforts effectively.
9. Reducing Greenhouse Gas Emissions: As a long-term strategy, work towards reducing greenhouse gas emissions to mitigate the effects of global climate change.
10. Adaptive Agriculture: Promote climate-resilient agricultural practices to reduce the impact of heatwaves on food production and farmers.
11. Heat-Resilient Construction: Encourage the construction of buildings and infrastructure that can withstand extreme heat conditions.

NDMA Guidelines:

• You think someone is suffering from the heat:
  1. Move the person to a cool place under the shade
  2. Give water or a rehydrating drink (if the person is still conscious)
  3. Fan the person
  4. Consult a doctor if symptoms get worse or are long-lasting or if the person is unconscious
  5. Do not give alcohol, caffeine, or aerated drink
  6. Cool the person by putting a cool wet cloth on his/her face/body
  7. Loosen clothes for better ventilation
• Emergency Kit
  1. Water bottle
  2. Umbrella/ Hat or Cap / Head Cover
  3. Hand Towel
  4. Hand Fan
  5. Electrolyte / Glucose / Oral Rehydration

Way Forward:

1. The National Action Plan for Climate Change (NAPCC) should be implemented in true spirit for inclusive growth and ecological sustainability.
2. Nature-based solutions should be taken into account, not just for tackling climate change-induced heat waves but also for doing it in a way that is ethical and promoting intergenerational justice.
3. Sustainable Cooling
4. Passive cooling technology, a widely-used strategy to create naturally ventilated buildings, can be a vital alternative to address the urban heat island for residential and commercial buildings.
5. The Intergovernmental Panel on Climate Change (IPCC) in the third part of its AR6 stated that ancient Indian building designs that have used this technology, can be adapted to modern facilities in the context of global warming.