Context:
Index article on the Hindu – What is heat index and why is it important to measure?
About Heat Index:
- Heat index, also known as apparent temperature, is a measure of how the temperature feels to humans.
- Important factors that determines heat index
- Relative humidity
- Air temperature
- There is direct relationship between the air temperature and relative humidity and the heat index – as the air temperature and relative humidity increase (decrease), the heat index increases (decreases).
- The heat index is meant to describe experienced temperatures in the shade
- It does not take into account heating from direct sunlight or physical activity, or cooling from wind.
- India Meteorological Department (IMD) has recently launched the Heat Index on experimental basis.
- Heat index is derived using the heat index equation similar to what is used by National Weather Service, National Oceanic and Atmospheric Administration (NOAA), USA.
Why is it important to measure heat index?
Hot air can hold more moisture than cold air. Therefore, when temperature rises, the air’s capacity to hold moisture also increases, thus affecting the apparent temperature or heat index. Humidity is typically higher during heat waves — which is why the heat index at the time is usually higher than just the temperature, because humid air can feel hotter to humans.
- 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.
Source: The Hindu
Previous year question
In the cities of our country, which among the following atmospheric gases are normally considered in calculating the value of Air Quality Index?
1. Carbon dioxide
2. Carbon monoxide
3. Nitrogen dioxide
4. Sulfur dioxide
5. Methane
Select the correct answer using the code given below.
[UPSC Civil Services Exam – 2016 Prelims]
(a) 1, 2 and 3 only
(b) 2, 3 and 4 only
(c) 1, 4 and 5 only
(d) 1, 2, 3, 4 and 5
Answer: (b)
