Evaporation
When water evaporates from Earth's surface, it changes from a liquid to a gas and rises upward to form clouds. This atmospheric water then returns to the planet's surface through precipitation and condensation. Precipitation is rain, snow, hail and sleet. Condensation causes water droplets to form as dew on plants and other objects; it occurs when warm, water-laden air passes over a colder surface.
Sublimation
Sublimation occurs when water changes from a solid to a vapor without passing through a liquid phase. It typically takes place at high altitudes, such as the tops of mountains, where the air pressure is much lower than it is at sea level. The combination of cold temperatures, low air pressure, strong winds and bright sunlight converts frozen water to water vapor, which then rises to form clouds.
Transpiration
Plants return water vapor to the atmosphere through a process called transpiration. They absorb water from the ground through their roots, and release excess water through their leaves. This water evaporates into the atmosphere, and contributes to the formation of clouds. According to the United States Geological Survey, as much as 10 percent of the water in the atmosphere comes from transpiration.
Precipitation
As the tiny water droplets in clouds collide and combine with each other, they grow larger and heavier. When the droplets become heavy enough, they fall as rain, snow, sleet or hail, depending on the air temperature. In this way, clouds can take water that evaporated from the oceans, and carry it to inland mountains, where it falls as snow. After the water falls back to Earth, the water cycle repeats through evaporation, transpiration and sublimation.