Climatic factors; Humidity and Wind

Atmospheric humidity

Absolute humidity

The amount of water vapour present in a unit volume of air is called absolute humidity. It is expressed in terms of percentage of water vapour in the unit volume of air at the certain temperature.

Relative humidity

It is the amount of water vapour in the air at specific temperature compared to the maximum water vapour that the air can hold without condensing. It is expressed by; \(\frac {P.(H_2O)}{P*(H_2O)} \times 100\)

P(H₂O)- a Partial pressure of water vapour in the air.

P(H₂O)- Saturation vapour pressure of air at the specific temperature.

Effects of humidity on organisms

• It influences the rate of transpiration in plants. Higher the humidity, lesser is the rate of transpiration.
• It influences the rate of perspiration in humans. So, at high humidity sweating is less.
• It is an important source of water for epiphytes like lichens, mosses.
• It plays an important role in the germination of spores of fungi.

Wind

The moving current of air is called the wind. Air moves from higher to lower atmospheric pressure. It is also one of the most important ecological factors which affect the life variously. Some of its effects are:

• The high velocity of wind causes breakage of branches and uprooting the trees.
• It causes lodging of crop plants.
• Strong wind increases the rates of evaporation and transpiration which lead to the desiccation of plants.
• It causes premature falling of flowers, buds, fruits, leaves etc.
• The constant unidirectional wind causes the development of flag trees or permanent bend of trees.
• The strong wind causes soil erosion that reduces the soil fertility. It also causes desertification.
• The excess wind causes drying of a shallow pond which affects the aquatic life.
• It helps in the dispersal of seeds, fruits, pollen grains etc.
• It also helps in the migration of flying animal like bird, insect etc.