Precipitation

Precipitation is any form of water that falls from the atmosphere to the Earth's surface due to gravity. It includes rain, snow, sleet, hail, freezing rain, and drizzle. As a central part of the hydrological cycle, precipitation redistributes fresh water and supports ecosystems, agriculture, and human society.

Formation: Precipitation begins with condensation and cloud formation. In warm clouds, droplets grow by collision and coalescence and fall as rain. In cold clouds, ice-crystal processes, including the Bergeron mechanism, produce snow and can generate hail. Freezing rain forms when rain falls through a shallow cold layer and freezes on contact.

Observation and measurement: Rain gauges record liquid precipitation; radar and satellite data help map precipitation fields. Types are reported by observers, with amounts typically expressed in millimeters or inches of water equivalent.

Types: Rain is liquid water. Snow is ice crystals. Sleet consists of ice pellets formed when raindrops partially melt and refreeze before reaching the ground. Freezing rain is rain that freezes on contact with surfaces. Hail consists of solid ice stones formed in strong thunderstorms. Drizzle refers to light, fine rain.

Distribution and impact: Global patterns vary with latitude, season, and topography. The tropics, monsoon regions, and highlands often receive heavy rainfall, while deserts are dry. Precipitation influences freshwater supply, agriculture, flood risk, and ecological processes.

Climate variability and change: Long-term trends and natural cycles affect precipitation frequency and intensity. Warming can increase atmospheric moisture and alter storm tracks, potentially raising extreme rainfall in some regions and drought in others.