The Heat Index, often referred to as the "apparent temperature" or "feels-like temperature," is a measure of how hot it actually feels to the human body when relative humidity is combined with the actual air temperature. It accounts for the fact that the body’s ability to cool itself through perspiration is impaired when humidity is high, making it feel hotter than the actual air temperature.
How the Heat Index Works:
Temperature: The actual air temperature is the baseline. As the temperature rises, the body naturally feels hotter.
Relative Humidity: This is the amount of moisture in the air expressed as a percentage. When humidity is high, sweat does not evaporate as quickly from the skin, which is the body's natural cooling mechanism. This slow evaporation makes it feel hotter.
Calculation of the Heat Index:
The Heat Index is calculated using a complex formula that takes both the air temperature and relative humidity into account. Here’s a simplified idea of how it works:
Higher Temperatures + High Humidity: The heat index rises sharply when both temperature and humidity are high, making it feel much hotter than the actual temperature.
Higher Temperatures + Low Humidity: If the air is dry, the heat index will be closer to the actual air temperature because sweat evaporates more easily, allowing the body to cool itself effectively.
Example:
- An air temperature of 90°F (32°C) with 50% relative humidity can result in a heat index of around 95°F (35°C). This means it would feel like 95°F instead of the actual 90°F.
Health Implications:
The Heat Index is important because it helps assess the risk of heat-related illnesses such as heat exhaustion or heat stroke. As the heat index rises, the risk of these conditions increases, particularly for vulnerable populations such as the elderly, young children, and those with preexisting health conditions.
Heat Index Chart:
The National Weather Service (NWS) and other meteorological agencies often provide Heat Index charts or tables, where you can look up the heat index based on the current air temperature and relative humidity.
- Heat Index 80°F - 90°F: Caution; fatigue is possible with prolonged exposure and activity.
- Heat Index 90°F - 103°F: Extreme caution; heat cramps and heat exhaustion are possible.
- Heat Index 103°F - 124°F: Danger; heat cramps and heat exhaustion are likely, and heat stroke is possible.
- Heat Index 125°F and Above: Extreme danger; heat stroke is highly likely.
Conclusion:
The Heat Index is a critical tool for understanding how hot it really feels outside, helping people take necessary precautions to avoid heat-related health issues. It’s especially important during summer months or in regions with high humidity.
Iranian coastal town recorded the highest heat index on 28th August 2024 =82.2degree Celsius heat index:
—the Dayrestan Airport (Iran)weather station recorded a temperature of 38.8°C at 10.30am on August 28.
Viewed alone, the temperature isn’t as alarming. But, with a relative humidity of 85%, it combines to give the HI, or “feels like” temperature, of 82.2°C.
— High heat index means the body unable to evaporate the precipitate. Therefore, heat buildup in the body causing heat stroke and heat related complications when heat index value is above 50 degrees.
—- if absolute air temperature is around 35 degrees and relative humidity of 80% then heat index will be 53 degrees that is not tolerable. Here, in Iranian coastal airport temperature =38.8degree Celsius with 85% relative humidity leads to heat index reaches to 82.2 degrees. Highly scorching heat build up causing the heat related hazards.
—- dry/ arid climate with high temperatures is bearable due to evaporation of sweat from the body that regulates body internal temperature and body feels comfortable and cooling internally.
—- dew point is the temperature when air unable to hold more moisture or water vapours as it has reached to saturation level.
—- due to climate changes and global warming the impact on air temperature produces the heat waves, droughts and floods. Moisture holding capacity increases with warmer air ie., 1 degree temperature increase leads to increase in moisture level by 7%.
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