Climate Change Impact on India and World – International Reports, Key Observations, etc.

What is heat index and why is it important to measure?


From UPSC perspective, the following things are important :

Prelims level: Heat index, heat stress, heat waves etc.

Mains level: Climate change and soaring temperatures, impacts and measures

What’s the news?

  • In August, the coastal regions of Iran bore witness to an astonishing and potentially life-threatening event: a scorching heat index of 70 degrees Celsius (°C). Public holidays were declared on August 2 and 3 due to what was described as unprecedented heat.

Central idea

  • The alarming incidents of rising heat temperatures are not isolated; Iran had already grappled with extreme heat earlier in the year when the Persian Gulf Airport recorded a heat index of 66.7°C. The dire consequences of such soaring temperatures demand our attention and action.

What is the heat index?

  • The heat index, also known as the apparent temperature or feels-like temperature, is a measure of how hot it feels to the human body when relative humidity is factored in along with the actual air temperature.
  • In essence, it quantifies the discomfort or perceived warmth caused by the combination of high temperatures and high humidity.

How is the heat index calculated?

  • Dr. Robert Steadman’s Formula: Dr. Robert Steadman, a professor at Colorado State University, developed a complex formula in 1979 to calculate the heat index. This formula considers various parameters, including air temperature and relative humidity.
  • Parameters in the Formula: The formula takes into account the following parameters:
    • Air temperature (in degrees Fahrenheit).
    • Relative humidity (expressed as a decimal, e.g., 50% RH becomes 0.50).
    • Coefficients specific to the formula (c1, c2, c3, c4, c5, c6, c7, c8, and c9).
  • Nonlinear Relationship: The formula is complex because it accounts for the nonlinear relationship between temperature, humidity, and how humans perceive heat.
  • Global Variations: Different countries may have their own variations of heat index calculations, but Dr. Steadman’s formula is widely recognized and used as a standard reference.

Significance of measuring the heat index

  • Accurate Perception of Heat: The heat index provides a more accurate representation of how hot it feels to the human body compared to the actual air temperature. It factors in relative humidity, which significantly affects human comfort in hot conditions.
  • Health Impact Assessment: Measuring the heat index is crucial for assessing the potential health risks associated with hot weather. It helps identify conditions that may lead to heat-related illnesses, including heat exhaustion and heatstroke.
  • Preventing Heat Stress: High humidity levels, considered in the heat index, can lead to heat stress. Monitoring the heat index assists in recognizing situations where heat stress is more likely to occur, prompting individuals to take the necessary precautions.
  • Issuing Public Warnings: Weather agencies and authorities use the heat index to issue heat advisories and warnings to the public. These warnings inform people about the heightened risks associated with high heat index values, encouraging them to take protective measures.
  • Workplace Safety: Measuring the heat index is vital for ensuring workplace safety, particularly in industries involving outdoor work or non-air-conditioned environments. It enables employers and workers to implement safety measures to prevent heat-related illnesses and injuries.
  • Emergency Preparedness: Emergency response and preparedness agencies rely on heat index information to anticipate and respond to heat-related emergencies. This includes managing heat-related illnesses and addressing the increased demand for cooling during heatwaves.
  • Adapting to Climate Change: With the increasing frequency and intensity of heatwaves associated with climate change, monitoring the heat index becomes essential. It assists in adapting to changing climate conditions and developing strategies to mitigate heat-related risks.

How does high humidity impact the human body?

  • Heat Stress: High humidity can lead to heat stress, where the body struggles to dissipate excess heat. The typical human core temperature range is 36.1 to 37.2°C. When the body can’t effectively shed surplus heat, the core temperature rises, potentially causing symptoms such as heat exhaustion, rashes, and an elevated heart rate.
  • Reduced Cooling: In high humidity, the body’s natural cooling mechanism, which relies on sweating and evaporation, becomes less effective. The saturated air makes it challenging for sweat to evaporate, hindering the body’s ability to lose excess heat. This results in discomfort and a heightened risk of heat-related illnesses.
  • Perceived Temperature: High humidity can make the air feel significantly hotter than the actual air temperature. This increase in perceived temperature, often reflected in the heat index, contributes to a sense of extreme heat and discomfort.
  • Dehydration Risk: To compensate for reduced evaporative cooling in high humidity, individuals may sweat profusely. This increased sweating can raise the risk of dehydration if fluid losses are not replenished adequately.
  • Respiratory Discomfort: Humid air can pose challenges for individuals with respiratory conditions like asthma. The added moisture in the air may make breathing more difficult, worsening respiratory symptoms.
  • Sleep Disturbances: High humidity can disrupt sleep patterns, as sleeping in a warm and muggy environment can be uncomfortable. Restlessness and difficulties falling or staying asleep may occur in such conditions.
  • Impact on Physical Activities: High humidity can hinder physical performance and work productivity. People may find it more challenging to engage in physical activities or perform tasks in hot and humid conditions.

Facts for Prelims: Heat-related Terminologies in News

  • Heat stroke: Heat stroke is a serious medical condition that occurs when the body’s temperature regulation system fails, and the body temperature rises to dangerous levels, usually above 104°F (40°C). It can lead to organ damage and even death if not treated promptly.
  • Heat cramps: Heat cramps are painful muscle contractions that can occur during physical activity in hot weather.
  • Heat wave: A heat wave is a prolonged period of excessively hot weather, which can be accompanied by high humidity levels. The World Meteorological Organization (WMO) defines a heat wave as when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5°C, and the normal minimum temperature is also exceeded.
  • Heat index: It is the measure of how hot it feels when relative humidity is added to actual air temperature. The higher the heat index, the hotter it feels.
  • Thermal stress: It is the stress on the human body caused by high temperatures, humidity, and solar radiation.
  • Urban Heat Island: It refers to the phenomenon where urban areas experience higher temperatures than surrounding rural areas due to human activities like transportation, industrialization, and construction.
  • Wet bulb globe temperature: It is a measure of heat stress in direct sunlight, which takes into account temperature, humidity, wind speed, sun angle and cloud cover.
  • Diurnal temperature range: It is the difference between the maximum and minimum temperatures in a 24-hour period. A low diurnal temperature range indicates high humidity and poor air quality.

Way forward: Measures to adapt

  • Recognize the Danger: Acknowledge that a heat index value of 67°C or higher can be extremely dangerous for both humans and animals, especially with direct and prolonged exposure.
  • Invest in Early Warning Systems: Develop and invest in early warning systems that provide timely alerts and advisories about extreme heat events. This helps individuals and communities prepare for and respond to heatwaves effectively.
  • Adjust Work Timings: Consider making changes to work schedules to avoid outdoor activities during the hottest parts of the day. This can reduce heat exposure and the risk of heat-related illnesses.
  • Find Sustainable Cooling Solutions: Identify and implement sustainable cooling solutions, such as the use of energy-efficient and environmentally friendly cooling technologies. Ensuring access to air conditioning and promoting better building designs for heat resilience are also important.
  • Promote Public Awareness and Education: Raise public awareness about the risks associated with extreme heat, and educate individuals and communities about heat safety measures. Knowledge empowers people to take proactive steps to protect themselves during heatwaves.


  • As we confront rising heat index values across the globe, our ability to adapt and mitigate the effects of extreme heat on human health and well-being becomes paramount. Proactive measures, informed by a comprehensive understanding of the heat index, are essential to safeguarding lives and ensuring a sustainable future in the face of escalating climate challenges.

Must read:

Heat domes, anticyclones and climate change: What’s causing heat waves across the world?

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