Wednesday, March 30, 2011

The Hydrologic Cycle


The hydrologic cycle refers to the process whereby water gets converted from its liquid or solid state into its vapor state. As a vapor the water has been capable of traveling considerable distances from its source prior to responding and returning to earth as precipitation. The hydrologic cycle may be having either a long or various short cycles. In the short cycles, water may evaporate from either marine or freshwater systems, condense almost immediately, and return as precipitation to the same system. In the long cycle the major source of water vapor has been the world’s oceans, which are having 97.3% of the earth’s waters. In this cycle a portion of the water evaporates and forms clouds that move inland.
Stages in the Hydrologic Cycle:
1.      Evaporation and Condensation: Water vapors get evaporated primarily from the oceans and then tend to condense around minute particles, termed nuclei, which have been suspended in the atmosphere. The nuclei generally are having small particles of organic matters, fine mineral particles, volcanic ash etc. Dust and smoke particles from industrial sources and automotive exhausts may be serving as nuclei and major factor in contributing to the contamination of rainwater. 
2.      Run off, stream flow and infiltration: When rain is falling on a terrestrial area, a portion of the water would be caught by vegetaion. This process is known as interception. The remainder of the water falls to earth, and a portion sinks into the soil surface by a process known as infiltration. The portion not infiltrated into the soil, called surface run off flows over the surface and gets discharged into streams. The water entering a stream by surface run off plus t6he water entering via ground water flow is known as run off. 
3.      Evapotranspiration: A large number of the precipitated water would be converted to vapor by evaporation and transpiration.s Evaporation refers to the process whereby molecules of liquid water absorb sufficient energy to leave the liquid state and enter the vapor state. Transpiration refers to9 the process whereby terrestrial and emergent aquatic vegetation  release water vapor to the atmosphere. In the process of photosynthesis all plants have been taking in liquid water and carbon dioxide and by a complex series of reactions convert these materials to carbohydrate, oxygen and water vapor. The water converted from liquid to vapor in transpiration has been quite considerable, and the ability of plants to remove water from both soil and aquatic systems can not be underestimated.
4.      Ground water: The most lengthy portion of the hydrologic cycle would get completed when groundwater gets returned to the earth’s surface. The return may take place by springs, transpiration, or by artificial means.

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