Hydrological or Rain Evaporation Cycle

Rain Evaporation Cycle is a process by which moisture from the surface of water bodies covering the earth's surface transferred to the land and back to the water bodies again. The input to Rain Evaporation Cycle is the solar energy. Due to this water from the water bodies evaporates and on cooling these water vapours form clouds. Further cooling makes the clouds to fall down in the form of rain, snow, hail or sleet, etc. known as precipitation. Precipitation includes all water that falls from the atmosphere to the earth's surface in any form.

a major portion (about 2/3rd) of this precipitation, which reaches the land surface is returned to the atmosphere by evaporation from water surfaces, soil, and vegetation and through surface or underground channels. Thus the cycle is completed. The amount of rainfall which runs off the earth's land surface to form streams or rivers is useful for generation of electric power. The precipitation that falls on hills and mountains in the form of snow, melts during warmer weather as run off and converges to form streams can also be used for power generation.

The hydrography or hydrology deals with the occurence and distribution of water over and under the earth surface. In other words it is the study of hydrological cycle, in which the water rises by evaporation from sea, is carried over the land, where it falls as precipitation and then rises again by evaporation or transpiration or flows back to ocean.