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Menopausal Mother Nature

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It’s hot and more than what that heat index tells you

Humans mainly adjust to heat by sweating and flushing, which occurs when blood is directed to capillaries near the skin to dispel the heat

Heat stroke is considered likely if the index rises above 125-130. Photo: iStock Heat stroke is considered likely if the index rises above 125-130. Photo: iStock

A heat index can underestimate perceived temperatures by more than 6.6 degrees Celcius, noted an analysis by the University of California (UC) published in journal Environmental Research Letters August 12 2022.

The heat index, calculated by meteorologists, measures how hot it feels. It rises with increasing humidity even as the temperature remains the same.

Heat stroke is considered likely if the index rises above 125-130. Meteorological agencies, including the United States National Weather Service (NWS), use this index.


Also read: Simultaneous heatwaves across 5 continents: What’s unfolding in front of us

The heat index gauges how the body handles heat when humidity levels are high and sweating is less efficient at cooling us down, the researchers noted.

                                                                                                                            Source: NWS

Humans mainly adjust to heat by sweating and flushing, which occurs when blood is directed to capillaries near the skin to dispel the heat.

David Romps, UC Berkeley professor of earth and planetary science, told Berkeley News:

Diverting blood to the skin stresses the system because you’re pulling blood that would otherwise be sent to internal organs and sending it to the skin to try to bring up the skin’s temperature. The approximate calculation used by the NWS inadvertently downplays the health risks of severe heatwaves.

The heat index was devised in 1979 by a textile physicist, Robert Steadman. He used a basic formula to determine warm, humid conditions’ relative ‘sultriness’.

His model considered how people adjust their internal temperature to maintain thermal comfort by — consciously changing the amount of clothing they wear or unconsciously adjusting their breathing, perspiration and blood flow to the skin.

Since then, the heat index has become widely used as an indicator of people’s comfort in the US. 

But Steadman left the index undefined for many conditions, now becoming increasingly common.

For example, for a relative humidity of 80 per cent, the heat index is not defined for temperatures above 31.1°C or below 15°C. Today, temperatures routinely rise above 32.2°C for weeks in some areas, including the Midwest and Southeast of the US.

This summer’s extreme heatwaves sparked massive wildfires and resulted in thousands of fatalities in Europe, according to media reports.

Some countries like France are entering their third wave of summer, with temperatures expected to reach over 37°C. 

The average temperature across the US crossed 24.6°C, making July 2022 the third-hottest in the country’s 128-year climate record.

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