18. Necessary Conditions for RAINFALL

(a) there should be sufficient amount of evaporation from the water bodies (airmass must be saturated with water vapour)

(b) there should be wind to carry the water vapour from one place to another, and

(c) there should be some way of decreasing the temperature of the moist air.

The rainfall does not occur unless these cloud droplets become so large that the air is not able to hold them in suspension. Rainfall occurs only when the cloud droplets change to raindrops. The diameter of a raindrop is about 5 mm and one raindrop contains about 8 million cloud droplets.