The Hydrologic Cycle
The hydrosphere is the sphere that contains all the water of the Earth system. This includes water in a gaseous state, liquid water found in rivers, lakes, and streams, and water in its solid state like that of glaciers and ice sheets. Water found in living plants and animals can be considered part of the hydrosphere. The water of the hydrosphere interacts with the other subsystems of the earth.
The hydrologic cycle refers to the movement of water through its various stores within the Earth system. The amount of water that cycles between the surface and the atmosphere is phenomenal. At any minute, nearly a billion tons of water is delivered to the atmosphere by evaporation and the same amount precipitated from it. The hydrologic cycle not only traces the movement of water through the Earth system, it is a path way for the movement of energy. Water is evaporated from tropical oceans where energy is abundant and is transported on the wind to high latitudes where energy is in short supply. There it condenses and gives off heat to the atmosphere. The exchange of energy from low latitudes to high latitudes helps maintain the energy balance of the Earth system.