Context: As per a recent report, Iran’s coastal region has recorded a scorching heat index of 70 degrees Celsius (°C) in the coastal part of the country, a metric at which survival of life is not impossible. Also, the region recorded a heat index of 66.7 °C.

About Heat Index

• The heat index, also known as apparent temperature, is a crucial indicator that measures how the temperature feels to humans based on a combination of air temperature and relative humidity.

• It provides a more accurate representation of how hot the weather actually feels compared to just the air temperature.

• In 2024, India is scheduled to launch its own heat index to quantify the impact of heat on its population and generate impact-based heatwave alerts for

• Dr. Robert Steadman's Formula: In 1979, Dr. Robert Steadman, a professor at Colorado State University, developed a complex formula to calculate heat index.

• This formula considers factors like temperature, humidity, wind speed, and barometric pressure to determine the apparent temperaturespecific locations.

How Heat index is measured?

• Dr. Steadman’s study considers a “typical adult human of either sex, with a height of 1.7 metres and a weight of 67 kg.” 

• This standardization allows for a consistent calculation of heat index applicable to a broad range of individuals.

• Inclusion of Dew Point: Dew point is a critical factor in heat index calculations.

• It represents the temperature at which air can no longer hold all its moisture, causing condensation.

• Dr. Steadman used a specific dew point value of 14°C in his calculations.

• This factor is crucial in assessing the sultriness or discomfort associated with a particular temperature-humidity combination.

• Alternative Indices: While Dr. Steadman's formula is widely recognized, some countries, like Canada, have developed their own indices.

• Canada uses Humidex, which considers temperature and dew point, but has its own specific formula for calculation.

• This emphasizes the importance of tailoring heat index calculations to local climate conditions.

India

• The heat index in India is in experimental basis, launched by India Meteorological Department (IMD).

Colour codes used for experimental heat index, according to IMD are as follows:

In 2024, India is scheduled to launch its own heat index to quantify the impact of heat on its population and generate impact-based heat wave alerts for specific locations.

Why a specific heat index is important?

• Moisture Capacity and Apparent Temperature: Hot air has a greater capacity to hold moisture than cold air. When the temperature rises, the air's ability to hold moisture also increases.

• This affects the apparent temperature or heat index, making humid air feel even hotter to humans.

• This is why the heat index is a more useful metric than just the temperature alone.

• Effects of High Humidity on the Body: High humidity during heatwaves can lead to heat stress.

• In these conditions, the body struggles to dissipate excess heat.

• Impact of Humidity: Conversely, in low humidity conditions, sweat can evaporate more efficiently, making the apparent temperature feel closer to the actual air temperature.

• Dangerous Heat Index Values: A heat index value of 67°C or above is extremely dangerous for both humans and animals with direct and prolonged exposure. At this level, heat-related illnesses become a serious risk.