Can heatwaves be deadly? All you need to know

Temperatures in India's capital Delhi reportedly soared to a record-high of 52.3 degrees Celsius on Wednesday, with the weather department warning of dangerous heat levels in the sprawling megacity. But how dangerous or deadly heatwaves can be?

The National Disaster Management Authority (NDMA) says heatwave conditions can result in physiological strain, which could even result in death.  Meanwhile, the World Health Organization (WHO) explains that deaths and hospitalisations from heat can occur extremely rapidly (over same day), or have a lagged effect (several days later). 

The global health body says high air temperatures can affect human health and lead to additional deaths. “Extended periods of high day and nighttime temperatures create cumulative physiological stress on the human body which exacerbates the top causes of death globally,” the WHO explains.

Heat may "result in accelerating death or illness in the already frail, particularly observed in the first days of heatwaves," the WHO says. It adds, "Even small differences from seasonal average temperatures are associated with increased illness and death."

How do you know if you are impacted by heatwave?

The health impacts of heat waves may involve "dehydration, heat cramps, heat exhaustion and/or heat stroke". The signs and symptoms, as per the NDMA and the WHO, are as follows:

1. Heat Cramps: Ederna (swelling) and Syncope (Fainting) generally accompanied by fever below 39°C i.e.102°F.

2. Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.

3. Heat Stoke: Body temperatures of 40°C i.e. 104°F or more along with delirium, seizures or coma. "This is a potential fatal condition," the authority says.

4. Altered human behavior: Heat conditions can alter human behavior, the transmission of diseases, health service delivery, air quality, and critical social infrastructure such as energy, transport, and water.

It is important to take all reasonable steps to lessen the effects of heat waves, and to seek medical attention as soon as possible if discomfort arises.

How to help if someone is suffering from the heat:

The NDMA list a few ways in which one must help those affected by the heat. These measures include:

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 the person is unconscious

5. Do not give alcohol, caffeine or aerated drink

6. Give the person ORS to drink or lemon sarbat/torani or whatever is useful to rehydrate the body.

7. Cool the person by putting a cool wet cloth on his/her face/body

8. Loosen clothes for better ventilation

9.  Take the person immediately to the nearest health centre. The patient needs immediate hospitalisation, as heat strokes could be fatal.

When is heatwave declared in India?

According to the India Meteorological Department, a heatwave is considered if maximum temperature of a station reaches at least 40°C or more for the plains and at least 30°C or more for hilly regions.

The IMD defines heatwaves as "a period of unusually high temperatures as compared to what is normally expected over a region." It says that the impact of heatwaves gets aggravated due to high humidity, high wind speed, duration of heat wave events and other such meteorological factors.

Heatwaves primarily occur in India from March to June, and in very rare instances, even in July. May is when the heatwave that is affecting India peaks.