Heat Index

Heat Index

The article covers “Daily Current Affairs” and the topic details “Heat Index”. The topic “Heat Index” has relevance in the “Ecology and Environment” section of the UPSC CSE exam.

For Prelims:

What is the heat index? 

For Mains:

GS3: Ecology and Environment

Why in the news?

Recently, Iran experienced a scorching heat index of 70°C, causing extreme survival issues. The country had to declare public holidays due to the heat. 

Heat Index

  • The heat index also called the apparent temperature, combines air temperature and relative humidity to describe how the temperature feels to the human body.
  • It’s crucial for human comfort because when the body overheats, it starts sweating to cool down.
  • Sweating’s cooling effect depends on the evaporation of perspiration.
    • High humidity slows down this evaporation process, making the body feel warmer.
    • Conversely, lower humidity speeds up perspiration, making the body more relaxed.
  • Therefore, there’s a direct relationship between air temperature, relative humidity, and the heat index.
    • As air temperature and humidity increase, the heat index also increases, making it feel even hotter.
    • Conversely, as air temperature and humidity decrease, the heat index decreases, resulting in a cooler sensation.

Calculating Heat Index

  • Dr. Robert Steadman, a professor at Colorado State University, introduced a complex formula for calculating the heat index in 1979.
  • His research considered an average adult human, with specified height and weight, to derive this formula.
  • The heat index calculation incorporates the dew point, the temperature at which air reaches its saturation point and condenses into water droplets.
    • Dr Steadman used a dew point of 14 °C as a parameter in his calculations.
  • Countries like Canada and the United States have developed heat index measures like the Humidex and NWS Heat Index, respectively.
  • India plans to launch its heat index in 2024 to assess the heat’s impact on its population and issue location-specific heat wave alerts based on this index.


Importance of Calculating Heat Index

  • It is essential to measure the heat index because it can help us to understand the risk of heat-related illnesses.
  • High temperature and humidity can cause heat stress, causing symptoms like fatigue, cramps, heat exhaustion, and heat stroke, which can be life-threatening when the body’s temperature reaches 104°F or higher.
  • The National Weather Service’s heat index chart indicates risk levels for heat-related illnesses, with 95°F or higher being dangerous and urging precautions to avoid such risks.
  • The heat index is crucial for public health officials to issue heat advisories and warnings, ensuring safety during hot weather.

With climate change, humans are likely to see more extreme heat events. This means that it is more important than ever to understand the heat index and to take steps to stay safe during hot weather.


Sources: Explained | What is heat index and why is it important to measure? – The Hindu 


Q1. With reference to Heat Index, consider the following statements: 

  1. The heat index, also known as the apparent temperature, is determined solely by air temperature 
  2. High humidity accelerates the evaporation of perspiration, leading to a cooler sensation in the human body.
  3. Dr. Robert Steadman introduced the concept of the heat index by incorporating factors like dew point.

Which of the statements given above is/are correct?

(a) 1 and 2 only

(b) 2 and 3 only

(c) 3 only 

(d) None 

Answer: (c) 


Q2. Consider the following: 

  1. Lower humidity levels slow down perspiration, resulting in a more comfortable feeling.
  2. The heat index varies directly with air temperature and humidity, increasing as these factors rise and decreasing as they fall.
  3. The dew point represents the temperature at which air becomes saturated with moisture and condenses into water droplets.

How many of the abovementioned statements are correct?

(a) Only one 

(b) Only two 

(c) All three 

(d) None 

Answer: (b)

Q3. Examine the importance of measuring the heat index and its relevance in understanding the impact of high temperatures on human health and the environment. 

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