• The fall of moisture or water over the surface of the earth from atmosphere is knon precipitation.
  • Precipitation includes rainfall, snow, hail, sleet, and frozen water in any form.


  • Itis loss of water from surfaces of oceans, rivers, lakes, and moist soils.
  • The water lost by evaporation is in form of vapours and is form of clouds.


  • It is the process by which water leaves of the plants.
  • Sometimes combined loss of water by evaporation and transpiration is referredas total evaporation of water.


  • Unevaporated portion of precipitation is known as run-off.
  • A part of precipitation water that falls on the surface gets evaporate and transpiratedan remaining partis call run-off.
  • Run-off water ultimately runs to the ocean through surface and sub-surface streams of water.
  • Water, flowing on the land is know surface run-off.
  • This water first reaches the streams and river, and then ultimately joins sea.
  • The portion of precipitation that infiltrates into the surface soil runs as subsurface run-off and joins streams and rivers.
  • If precipitation is denot by P and total evaporation and various run-offs are denot by E and R respectively,
  • Then all the three elements can be connect mathematically as follows:

P = R + E.