Rainfall is the result of water vapor condensing and precipitating, forming droplets that fall from clouds due to gravity. It is an important part of the water cycle.
Condensation occurs when the air cools and becomes saturated. Clouds form when water condenses on particles in the air. The air can be cooled in several ways. Adiabatic cooling is caused by rising and expanding air. Conductive cooling occurs when air is affected by a colder surface. Radiative cooling is caused by infrared radiation, and evaporative cooling occurs when the air is saturated due to evaporation.
All of these forms of cooling can lead to the saturation of the air, condensation and precipitation. These processes may lead to the formation of clouds and water droplets, which leave the air as rainfall.