Approximately 505,000 cubic kilometres (121,000 cu mi) of water falls as precipitation each year: 398,000 cubic kilometres (95,000 cu mi) over oceans and 107,000 cubic kilometres (26,000 cu mi) over land. Precipitation is a major component of the water cycle, and is responsible for depositing fresh water on the planet. The movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah regions. Most precipitation occurs within the tropics and is caused by convection.

On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation. Thundersnow is possible within a cyclone's comma head and within lake effect precipitation bands. Lake-effect snowfall can be locally heavy. Where relatively warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones. Eventually, the cloud droplets will grow large enough to form raindrops and descend toward the Earth where they will freeze on contact with exposed objects. Provided there is necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely nimbostratus and cumulonimbus if significant precipitation is involved. A stationary front is often present near the area of freezing rain and serves as the focus for forcing and rising air. This process is typically active when freezing rain occurs. Moisture that is lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. Short, intense periods of rain in scattered locations are called showers.

Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Thus, fog and mist are not precipitation but colloids, because the water vapor does not condense sufficiently to precipitate.

Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor (reaching 100% relative humidity), so that the water condenses and 'precipitates' or falls. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. Some parts of a country can be much wetter than others, so it is not an accurate depiction of the wettest and driest places on earth. Mean precipitation based on global high resolution climate data (CHELSA) Countries by average annual precipitation. For other uses, see Precipitation (disambiguation).

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