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HEAT INDEX

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HEAT INDEX

WHY IN NEWS ?

  • Recently, Iran recorded a scorching heat index of 70 degrees Celsius (°C) in the coastal part of the country.

MORE ABOUT THE NEWS:

  • Iran had declared public holidays on August 2 and 3 on account of “unprecedented heat”.

  • This is not the first time this year that Iran is dealing with extreme heat.
  • In July, U.S.­based weather observer Colin McCarthy reported that the Persian Gulf Airport recorded a heat index of 66.7 °C.

WHAT IS HEAT INDEX ?

  • Heat index, also known as apparent temperature, is a measure of how the temperature feels to humans.
  • Relative humidity is an important factor that determines heat index, along with air temperature.

MEASURING HEAT INDEX :

  • Dew point, which is the temperature at which gas is transformed into a liquid state, is an important factor in the calculation of heat index.
  • In terms of atmospheric moisture, it’s the temperature at which air cannot hold any more water vapour, and droplets of water begin to form. Dr. Steadman used 14 °C as the dew point in his calculations.

IMPACT OF HIGH HUMIDITY AND EXTREME HEAT:

  • High humidity can lead to heat stress, meaning the body is unable to get rid of excess heat.
  • Humans usually maintain a core temperature in the range of 36.1 to 37.2 °C.
  • When the body is unable to get rid of excess heat, the heart rate increases due to a rise in core temperature, leading to heat ­related exhaustion and rashes, among other symptoms.
  • It can also be fatal if not addressed promptly.
  • At high temperatures, the human body can lose excess heat through perspiration and cool itself.
  • But when humidity is high as well, it is difficult to sweat and then for that sweat to evaporate because the air around is already saturated with moisture.
  • This makes it difficult for the body to lose heat.
  • On the other hand, if the humidity is low, evaporation of sweat is easier, thus making the apparent temperature feel close to the actual air temperature.
  • This is why a measure of heat index is more useful than just the temperature to gauge the impact of heat on humans.

SYLLABUS: PRELIMS, ENVIRONMENT

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