Humidity
Topic: Water in the Atmosphere: Humidity, Condensation, Clouds and Precipitation · NCERT: Class 7, Ch 2 "Understanding the Weather"; Class 9, Ch 3 "Atmosphere and Climate"; Class 11, Ch 10 "Water in the Atmosphere"
Meaning
Humidity is the water vapour in the air. It makes up between 0 and about 4 per cent of the atmosphere by volume. The vapour comes from evaporation (water turning into vapour from seas, lakes and rivers) and transpiration (vapour given out by plants). It is measured in three ways:
- absolute humidity: grams of vapour in a cubic metre of air;
- specific humidity: grams of vapour in a kilogram of air;
- relative humidity: the vapour present as a percentage of the most the air could hold at that temperature.
Humidity falls quickly with height. It decides whether dew, fog, clouds and rain can form.
Example
Clothes dry slowly in humid Kochi on the Kerala coast and quickly in dry Jaipur in Rajasthan. Dry weather has a relative humidity of about 20–40 per cent. Humid weather has about 60–80 per cent.
Don't confuse with
- Relative humidity: this is only one measure of humidity. It changes when air warms or cools, even if no water is added or removed.