Heat Wave

Qualitatively, a heat wave is a condition of air temperature that becomes fatal to the human body when exposed. This generally comes as a heatstroke.

What is a heatstroke?

When heat overwhelms our body’s ability to manage its temperature it is known as Heatstroke. It is a severe illness that results when the body temperature goes beyond 40oC (Hyperthermia). Symptoms: It presents itself as red skin, headache, dizziness and confusion. It can become a life-threatening condition due to seizures, kidney failure and potential multi-organ failure, including heart failure. Classical (Non-exertional) heat stroke occurs due to substances that inhibit cooling (alcohol). Exertional heat stroke occurs due to severe physical activity in hot weather. During severe heat waves both types of heatstroke become common.

Quantitatively, it is defined based on the temperature thresholds over a region in terms of actual temperature or its departure from normal. In certain countries, it is defined in terms of the heat index based on temperature and humidity or based on the extreme percentile of the temperatures.

Defining Heat Waves:

According to IMD, Heatwave is considered if the maximum temperature of a station reaches:

1. At least 40°C or more for Plains,
2. At least 37°C or more for coastal stations and
3. At least 30°C or more for Hilly regions.

In order to declare a heatwave, the following criteria are used to declare heat wave:

To declare a heat wave, the following criteria should be met at least in 2 stations in a Meteorological sub-division for at least 2 consecutive days and it will be declared on the second day.

1. 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
2. Based on Actual Maximum Temperature (for plains only):
   • Heat Wave: When actual maximum temperature ≥ 45°C
   • Severe Heat Wave: When actual maximum temperature ≥47°C

Occurrence of Heat Waves in India

In India, Heat waves typically occur between March to June, and in some rare cases even extend till July. In 2024, around 700 deaths were reported due to heatwaves in India, with record-breaking 37 cities surpassing 45^oC mark.

Criticism

In order to see the actual impact on the human body, temperature alone is a poor index. It is not the temperature alone that impacts the human health. Several other parameters can adversely impact our health too:

1. Wind – dry hot air such as in the case of Loo, which blows from the southwest direction in Rajasthan just before Monsoon rains, has a severe drying effect on vegetation, livestock and humans. It creates fatal heatstroke in the north India.
2. Humidity of air – Moist and warm air depletes the capacity of air to evaporate. It makes us feel sweatier, reducing our natural ability to cool down with sweating. This too creates a strong possibility of heat stroke.

Thus, temperature alone cannot be the right parameter to declare heat waves. Heat Index can be a better parameter to declare heat waves in humid environments.

What is the Heat Index?

The Heat Index is a parameter that considers both temperature and humidity to calculate the apparent temperature or “feel like” temperature for human beings.  The Heat Index has been launched on an experimental basis by the India Meteorological Department (IMD). Indication of Heat Stress: It helps in understanding the impact of humidity on high temperatures and how it contributes to human discomfort during hot weather. 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 colour codes: Green: Experimental heat Index less than 35°C. Yellow: Experimental heat Index in the range of 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 heat waves. It assists in making informed decisions and formulating heat action plans to ensure the well-being of the population.

Reasons for Severe Heat Waves:

1. Delayed arrival of the southwest monsoon.
2. Climate change is driving temperatures higher as well as increasing the frequency and severity of heat waves in India.
3. Unplanned urban development, densely populated areas, increasing urban sprawl and unique challenges associated with it such as the Urban Heat Island effect in cities are exacerbating the impact of heat waves.
4. Changes in land use and land cover – clearing of forest for agricultural and urban uses.

Response to Heat Waves:

Heat waves are traditionally not recognized as disasters. However, its severity and occurrence have made it an impediment to treating it as a disaster in the future.

Non-recognition as a disaster:

Heat Wave has not been notified as a Disaster as defined under DM Act, 2005 by the Govt yet. Heatwave is not even notified in the list of 12 disasters eligible for relief under National/ State Disaster Response Fund norms.

This makes it extremely difficult for the states to spend money for immediate response, and for insurance claims to be made in response to heat waves.

Tamil Nadu has become the first state in 2024 to classify heatwaves as a State-specific disaster, allowing for organised relief efforts and financial aid for the families impacted by severe heatwaves.

NDMA Guidelines on Heatwaves

The National Guidelines for Preparation of Action Plan – Prevention and Management of Heat Wave were released by NDMA in 2019. It proposes the following measures to deal with the incidences of Heat waves:

1. Government Engagement: Mandating participation from State and district government leaders, municipal health agencies, disaster management authorities and local partners.
2. Appointing State Nodal Agency and Officer to conduct tabletop exercises, simulations and drills before the summer as well as to ensure coordination among various stakeholders.
3. Vulnerability assessment and establishing Heat-Health threshold temperatures: The state should coordinate with IMD to develop threshold temperatures.
4. Drafting and developing Heat Action Plan: The State Nodal Officer can coordinate with the local IMD office to start receiving summer season forecasts and release early warning and daily alert system with colour codes.
5. Implementation and monitoring: Do’s and Don’ts during a heat wave should be available in the local language and disseminated through media including social media.
6. Evaluating and Updating the plan: After every heat season, the city or state must assess the efficacy of the heat action plan, including processes, outcomes and impacts.
7. Strategies for reducing extreme heat exposures and adapting to climate change (Long Term): States should consider mitigation strategies, such as increasing green cover in a city to reduce its incidence.

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