Hydrological Cycle: Mechanism of Hydrological Cycle (With Statistics)

Hydrosphere, atmosphere and lithosphere of water are regularly included in the water cycle or hydrological cycle. Water reaches in the atmosphere through evaporation from seas, lakes, rivers, soil moisture and transpiration from plants etc. and according to changing climatic conditions condenses in the form of clouds and again reaches the hydrosphere and lithosphere.

This cyclical movement of water in different forms is called hydrological cycle. In the water cycle, movement of water takes place independently within different realms. Among these, vertical and horizontal movement of air transferring moisture from one place to other in the atmosphere, movement of water through sea streams in the hydrosphere and movement of water through rivers and glaciers towards the sea in the lithosphere are included. Similarly, vaporized water from soil and evapotranspirated water from plants reach’s the groundwater through infiltration.

Water is a basic resource on the earth, which maintains its promi­nence among all natural resources. As a companion of nature, water provides the basis for all living organisms on the earth. Its distri­bution on the earth is found in many forms at various places. Its form keeps changing according to location and climate.

It remains in gaseous form in atmosphere as water vapour, in solid form as micro snow granules and in liquid form as drops of water. All these forms keep changing because of change in temperature and they affect weather pattern. On the earth living community needs regular supply of water.

This water should be balanced and qualitative, which is mainly available in rivers, lakes and aquifers. Sea water is not suitable for human consumption because of being saline. Most of the fresh water is frozen in the form of snow which is sufficiently beyond the reach of man and its use is also normally possible.

Every year, only one per cent of the water available on earth goes in the water cycle. Total quantity of water found in the water cycle has been estimated to be about 1,384 million kms’. This cycle is quite complicated from the point of view of different types of branches and water reservoirs. Major portion of the water as companion of the water cycle remains in seas and oceans (Table 5.1). Only 2 per cent of water is pure while the remaining part is frozen in the form of snow.

Rivers play an important role in the universal water cycle because they allow movement of water from the ground towards seas and oceans. They flow water with fast speed and are not able to store it, whereas lakes store more water as compared to rivers. There are about 250 vast lakes on the earth. Water moves in different storage places but its speed is calculated in the water cycle at different rates.

Water remains stored in oceans, snow caps and rocks for a very long time whereas, it remains for a very short period in rivers as well as atmosphere, though they have a great importance in the water cycle.

Mechanism of Hydrological Cycle:

There are many agencies which affect movement of water cycle on the earth. Condition and position of moisture are continuously changing relatively and the moisture which is received by the atmosphere can again be received by the ground or oceans in the form of water, dew, snow, frost etc. Hence, due to changes in condition and position, obstacles are created in the process of the hydrological cycle.

Water of oceans takes the form of vapour due to solar radiation and enters the atmosphere. Air flowing in oceans towards the ground gives speed to this vapour and transfers it from one place to other. After this, when water vapour condenses, it rains on the surface of the earth and the water received on the earth from precipitation flows on the surface in the form of drains and rivers and ultimately enters the oceans.

Solar energy increases the speed of water cycle. Some part of the water received from rain is lost through transpiration by plants and some part again reaches the atmosphere through evaporation of water from rivers, ponds and lakes etc. Some part of precipitation on ground level goes underground through infiltration.

This water reservoir in soil is called ‘soil water reservoir’ from where transpi­ration through plants continues, but some part again comes to the ground level in the form of water sources. Some part of soil water reservoir moves downwards. The portion of water stored below the surface is called underground water.