IMD issues advisory on heat waves: What you need to know to stay safe

The criteria for declaring a heat wave include, if the maximum temperature of a station reaches at least 40 degrees Celsius or more for plains and at least 30 degree Celsius or more for hilly regions.

Hyderabad: A heat wave is defined as a period of excessively high temperatures that are fatal to humans when exposed.

According to an advisory issued by the India Meteorological Department (IMD), a heat wave is determined based on temperature thresholds over a region, either in terms of actual temperature or its departure from normal.

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The criteria for declaring a heat wave include, if the maximum temperature of a station reaches at least 40 degrees Celsius or more for plains and at least 30 degree Celsius or more for hilly regions.

There are two categories of heat wave- heat wave and severe heat wave. A heat wave is considered when the actual maximum temperature is ≥ 45°C, while severe heat wave is considered when the actual maximum temperature is ≥ 47°C.

If the above criteria are met in at least two stations in a meteorological sub-division for at least two consecutive days, it is declared as a heat wave on the second day.

Heat waves typically occur from March to June, with May being the peak month of the heat wave over India. The health impacts of heat waves can range from dehydration, heat cramps, and heat exhaustion to potentially fatal heat stroke.

Heat cramps are characterized by edema (swelling) and syncope (fainting), generally accompanied by fever below 39°C (102°F).

Heat exhaustion is marked by fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps, and sweating. Heat stroke, on the other hand, occurs when the body temperature reaches 40°C (104°F) or higher, along with delirium, seizures, or coma, and can be a potential fatal condition.