Water Cycle

As we all know, water is tasteless, odourless, colourless and a universal solvent, which is mainly composed of hydrogen and oxygen atoms. Water exists in three states of matter- solid, liquid and gaseous. It is the most essential and abundant element found on the planet earth. An average adult human body is composed of 50 to 65% water.

Our planet earth is called the blue planet because of the presence of an abundance of water .i.e the three-fourths of the earth’s surface is covered with water bodies and water cycle play an important role in maintaining the balance of water and also in the maintenance of lives and ecosystems on the planet.

Let us learn more about the water cycle and how it is recycled in a cyclic pattern.

What is the Water Cycle?

The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes the continuous movement of water on, above and below the surface of the Earth. It is the natural process which moves water away from the surface of the earth atmosphere and again back into the earth atmosphere with the help of solar energy and wind.

During this biogeochemical cycle process, water changes its state from one phase to another and the total number of water particles remains the same. The changes in the state of water include evaporation, melting, freezing, sublimation, condensation, and deposition. All these changes require the application of energy.

Various Stages of Water Cycle

Water Cycle

A Diagrammatic Representation of Water Cycle

There are many processes involved in the movement of water. Listed below are different stages of the water cycle.

Melting – It is a physical process, which changes a solid object into a liquid state when the heat is applied. During melting, the solid ice gains thermal energy and melts into liquid water.

For example–Ice cubes in a cold drink gradually melts.

Sublimation –It is the transition of a substance directly from the solid phase to the gaseous phase when the heat is applied. During sublimation phase solid ice directly converts to a gaseous vapour without attending its liquid state.

For example- On a cool, dry winter day,  snow on the banks shrink, or ice constantly evaporates into vapours, without becoming slushy and wet.

Evaporation – Evaporation is one of the major processes of the water cycle. It occurs when water receives complete thermal energy required for converting its phase from the liquid (water) to a gaseous (water vapour). In this stage, water vapour gets mixed with the air and disappears.

For example: During transpiration and excretion in plants, the excess amount of water molecules present in plants are evaporated into the air in the form of vapours.

Condensation – It is a physical process in which a solid state is changed into a liquid state. This stage is the reverse of the Evaporation process.

In Condensation phase, water vapour present in the atmosphere is cooled or condensed and returned back to its original liquid state.

For example, a cold water bottle kept outside on a hot summer day often collects water droplets. This is because water vapour in the air condenses when it is cooled by the cold water bottle.

Deposition –When thermal energy is removed from water vapour it changes to a solid state. Deposition occurs when water vapour changes its state directly from a gaseous to a solid.

This stage is the reverse of the sublimation process.

For example, deposition occurs high in the atmosphere where the temperature is very low. In these conditions, water vapour forms snow without attending its liquid state.

Precipitation – This process can be simply defined as the forms of moisture arising from clouds and reaching back to the ground. It is the part of the water cycle in which atmospheric water vapour gets condensed, forming large water droplets and fall back to earth in the form of a rain or rain droplets with the help of the gravity. Precipitation usually occurs in the low-temperature regions. During this process, the surface water gets frozen up and get changed into solid ice as ice is slightly denser than water. This is the reason why lakes and ponds develop an ice layer that floats on the water during the winter season.

Freezing, condensation, and deposition are processes that occur as a result of a decrease in the thermal energy of water particles.

Changes with the Seasons

Seasons are also involved in maintaining the balance of water in this ecosystem. As the spring season arrives the snow or the forms of ice crystals present in the earth’s atmosphere melts and flows into the different water bodies, including streams, rivers, ponds, lakes and finally into the ocean. A very few amounts of melted snow sinks into the ground, becoming groundwater. This surface water evaporates and the water cycle is repeated.

The water cycle is mainly involved in maintaining the level of water on the earth’s surface. The entire cycle can be summarized as, in the process of hydrologic or water cycle, water from different water bodies gets warm-up and are converted into water vapours. This gaseous form of vapours is evaporated and condenses into tiny droplets that form clouds. As the clouds get heavy the water falls back to the earth in the form of rain or hail or snow, which is called precipitation. The rainwater is either absorbed into the ground or flows back into the oceans, ponds, rivers, and lakes, where it gets, evaporates back into the atmosphere.

Stay tuned with BYJU’S to learn more about the Water cycle and other related topics @ BYJU’S Biology

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