Water occur on the earth and atmosphere in all three states (liquid, gas, solid). There is endless circulation of water between earth and atmosphere. This circulation is called hydrological cycle.
This cycle has no beginning or end and its many process occurs simultaneously. This cycle gets its energy from the Sun. Sun and Coriolos force (due to this force, wind moves in different direction) play important role in completion of hydrological cycle. Sun evaporates water and Coriolis force, by controlling wind circulate the water vapour, where precipitation occurs.
Components of Hydrologic Cycle
When the water come into contact with radiation generates from sun, it turns in vapour. This process is called evaporation.
In hydrological cycle, evaporation mainly occur from ocean. Rivers, lakes and ponds are also contribute in evaporation process but in very small quantity.
As the evaporation continues, the amount of vapour in atmosphere goes on increasing, after reaching a certain amount, the vapour condense and come to earth’s surface in solid or liquid form, this is called precipitation.
As the air temperature decreases, its moisture holding capacity decreases.
The precipitation which is intercepted by leaves, branches of plants and the forest floor and does not reach the soil is known as interception in hydrological cycle. Or we can say some amount of precipitation is evaporated back to the atmosphere and another part is intercepted by vegetation, structure etc. from where it may either evaporated back to atmosphere or move down to ground surface. For example, amount of rainfall on the roof of the building is intercepted rainfall or simply interception.
When the water come into the earth surface, some portion of it penetrate the ground and increase the moisture content of soil beneath earth surface. This water is called infiltrated water the process is known as infiltration.
With the help of infiltration, ground water level of underground water bodies increases. Infiltration is more in villages than in comparison to urban areas, the urban areas have more pacca roads= which is treated as impervious strata. Also the infiltration is more in forest area in comparison to desert area because the trees makes the surface pervious and increase the infiltration.
Vegetation use the ground water or soil moisture for their growth. This moisture again convert in evaporation through vegetation. Water extracted by plant’s roots, transported upward through its stem and diffused into the atmosphere through tiny openings in the leaves is called transpiration water and the process is known as transpiration.
The portion of precipitation which come on the surface and reach the stream channel by above and below the surface of earth is called runoff
- The portion of precipitation that reach the stream after reaching on surface, only from above the surface is called surface runoff.
- The runoff reach in stream channel is called stream flow.
- Runoff means the draining or flowing off of precipitation from a catchment area through a surface channel.