Humidity and Its Measurement

Definition of Humidity

Humidity refers to the amount of water vapor in the atmosphere. Water vapor forms when liquid water changes into a gaseous state through evaporation.

Relationship Between Humidity and Temperature

Humidity is closely related to atmospheric temperature.

1. Heat from the Sun increases the temperature of water bodies, causing evaporation from seas, rivers, lakes, and other water sources.
2. Plants release water vapor into the atmosphere through evapotranspiration.
3. Higher temperatures lead to increased humidity, while lower temperatures reduce humidity levels.

Importance of Humidity

1. Helps predict the amount of rainfall.
2. Affects temperature estimation in a specific area.

Measuring Humidity

Humidity is measured in percentage (%) using an instrument called a hygrometer.

Types of Hygrometers

There are two types of hygrometers:

1. Direct-reading Hygrometer – Measures humidity and records the percentage of water vapor in the air using arrows, without thermometers.
2. Wet and Dry Bulb Hygrometer – Consists of two thermometers:
   • Wet-bulb thermometer: Wrapped in muslin cloth and dipped in water to stay moist.
   • Dry-bulb thermometer: Left exposed without muslin.

Interpreting Humidity Readings

1. No difference between wet and dry bulb readings → Very high humidity (air is saturated with water vapor).
2. Small difference between readings → High humidity.
3. Large difference between readings → Low humidity.

The hygrometer records daily humidity levels in percentage. Both thermometers are housed in a Stevenson screen for accurate readings.

Humidity measurement chart

Hygrometers