The two processes that contribute water vapor to the atmosphere are:
- Evaporation
- Transpiration
Evaporation occurs when water from surface bodies (like oceans, lakes, and rivers) turns into vapor and enters the atmosphere. Transpiration is the process by which plants release water vapor into the air through small openings in their leaves.
Precipitation refers to water falling from the atmosphere (as rain, snow, etc.), and runoff is the movement of water (usually from precipitation) over land, neither of which contribute to adding water vapor to the atmosphere.