The Earth and its various abiotic and biotic systems are greatly influence by water. Water is essential for life and plays an important role in atmospheric and lithospheric processes. The hydrologic cycle is used to model the storage and movement of water between the biosphere, atmosphere, lithosphere and hydrosphere.
Water is stored in the atmosphere in all three states of matter.
Water vapor in the atmospheric is commonly referred to as humidity. If liquid and solid forms of water can overcome atmospheric updrafts they can fall to the Earth's surface as precipitation. The formation of ice crystals and water droplets occurs when the atmosphere is cooled to a temperature that causes condensation or deposition. Precipitation can be defined as any aqueous deposit, in liquid or solid form, that develops in a saturated atmospheric environment and generally falls from clouds. A number of different precipitation types have been classified by meteorologists including rain, freezing rain, snow, ice pellets, snow pellets, and hail.