Understanding the Weather
Humidity
Learn what humidity is, and how it is measured.
Humidity is how much water vapour is in the air. It depends on temperature, wind, pressure and place.
Two facts from Grade 6 Science explain how humidity feels:
- when water evaporates, it cools things
- when the air is already full of water, water evaporates slowly
Put them together. Your body cools itself by sweating: the sweat evaporates off your skin. On a humid day the air is already full of water, so sweat dries slowly, you cool slowly, and you feel hot and sticky. Wet clothes take ages to dry for the same reason.
It is measured as relative humidity: 0% means no water vapour at all (never happens in nature) and 100% means the air can't hold any more. Usually:
| Weather | Relative humidity |
|---|---|
| dry | 20%–40% |
| humid | 60%–80% |
The instrument is a hygrometer. Places by the sea, like Kochi or Mumbai, are usually much more humid than inland places like Jaipur, but you need the numbers to compare properly (say, Kochi with Mangaluru).
Humidity matters beyond comfort: food factories need to control it, and museums keep their rooms dry to protect old objects.
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