Why is it so hot?

Why is it so hot?

Its a sweltering mid May day in Mumbai, the peak of Indian summer season. Being a tropical city, Mumbai is expected to be warm, and the humidity adds up to the misery. In such a situation, if one guesses the temperature, they might say a high 30 or 40 degrees Celsius. Although, quite many times, the temperature measurement defies this expectation – its usually considerably lower than what was assumed. Why?

Lets head to human anatomy for a while. Our body carefully controls its temperature at around 37 degrees Celsius. Extra heat is expelled as sweat, which evaporates and cools down our body as a result. Humidity is the measure of the water vapor content in the air, and evaporation depends on humidity. This has been a long known fact. More the humidity, slower the evaporation and vice-versa.

So imagine this. It is 35 degrees in Mumbai, the relative humidity is 74%. The body naturally heats up due to the surrounding temperature, and starts sweating to bring the heat down. But then, with such high humidity, the accumulated sweat is not evaporated quickly. This results in lower heat loss from the body, and the temperature builds up inside you. You start feeling its hotter than what it really is.

The temperature that the body feels due to the influence of humidity is called the apparent temperature, given by the Heat Index. Many weather apps display this temperature as the “Feels Like” temperature. Given below is a table which approximates the apparent temperature.

With the above table as reference, and the example conditions of 74% humidity and 35 degrees air temperature, you will be feeling a temperature as high as 52 degrees. This is however, an approximation, and there are always processes in nature which prevent such high heating. Therefore, the temperature might be lower than the one approximated by the chart, but it gives us the basis to reason upon why it feels warmer than it actually is.

So, the next time when someone says its too hot near the coasts, you can pull out this chart and tell them what temperature their body is feeling. Quite a surprising thing to know, if you ask me!

Until next time!

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