Water cycle: Definition, Process, Importance


This article explains in detail the process and importance of the water cycle on earth. It is also known as the hydrologic cycle, which involves steps such as evaporation, sublimation, condensation, precipitation, and many more.

Introduction

It is known that water in the form of vapours evaporates from the earth. Water is essential for every living organism present on earth. In its absence, survival becomes difficult. It is present in all three phases. It is present as solid ice, water as liquid and vapours as gas. Water evaporates from solid or liquid into a gaseous form. From the atmosphere, it again enters the earth surface by changing from vapour into liquid or snow form. These changes are continuously taking place all the time.

Hydrologic cycle

Water cycle which is also known as the hydrologic cycle is a continuous process. Water evaporates from various water sources or bodies present on the earth. The liquid evaporates in the form of water vapour. Clouds are formed. Water then enters back the earth surface in the form of snow and rain. When water drops on the earth surface, the rainwater enters the ground and joins the water bodies. Also, root hairs of plants are in direct contact with soil. They absorb water and essential nutrients from the soil. Water movement takes place in an upward direction. It then enters the atmosphere by transpiration process. In this way, groundwater enters the atmosphere.

Evaporation

It is part of the hydrologic cycle. Through this process, water gets transported from the earth and enters the atmosphere. The liquid form is transferred into a gaseous state. Water gets evaporated into water vapour when some of its molecules achieve kinetic energy. Thus, they leave the water bodies or water surface and enters the atmosphere. Evaporation of water mainly takes place from the largest water bodies on the earth surface such as oceans. Apart from them, rivers, lakes, ponds also contribute. Some amount of groundwater gets evaporated through transpiration and some amount through moist soil.

Sublimation

It is a process in which evaporation takes place directly from ice and snow. In this case, ice and snow do not melt to become water and then evaporation takes place. Instead, ice and snow directly enter the atmosphere in the form of water vapour.

Evapotranspiration

It is also known as total evaporation. Plants and trees absorb water from the soil and evaporate it in the atmosphere through transpiration process. Also, water from the earth surface, water bodies, moist soil, ice, snow evaporates and forms clouds. Evapotranspiration is a total of all the processes. It includes the evaporation of water from every living and non-living thing that can be vegetation or from water bodies.

Condensation

The condensation process is one in which water from the gaseous state will get transferred to the liquid state. Water vapour will get transferred to water which will enter back the earth surface in the form of rain. Air contains moisture due to the presence of water vapour in it. Water vapour remains in the troposphere and supplies moisture for clouds, frost, dew and fog. Condensation process will initiate when the concentration of water vapour increases in the air. When the air is not able to receive any more water from the surface of the earth through evaporation process due to enough amount of moisture already present in it, condensation begins, and water vapour gets released to form precipitation.

Precipitation

It is a process in which water reaches the earth surface in the form of rain. The water that free flows the surface of the earth gets distributed in different ways. Most of the water runs the surface of the earth, joins the river and into the sea. Some of it flows underground and becomes groundwater. Some of it is used by vegetation. Some of it gets evaporated back in the atmosphere.

Why is the water cycle important?

Water is an essential element for every living being on this earth. Life is present on the earth due to the presence of water on this planet. Water is a part of everything. It is present underground, in the soil, in the air and the water bodies. Without proper maintenance of water cycle or any disruption in it, we may have to face severe consequences in the forms of heavy rain, drought, floods and other calamities. Below-mentioned is a few points that describe the importance of the water cycle.

  • It brings climatic changes-
    The water cycle has a very powerful effect on climatic changes. It directly as well as indirectly affects the climate of an area, country, and altogether brings changes in global climate. The heat energy of the sun evaporates water from the surface of the earth. Evaporation decreases temperature. Without the water cycle, scarcity of water vapour in the air will make it dry and increase the temperature. Thus, water cycle produces a cooling effect and makes life sustainable on this planet. Without the water cycle, sea level will keep increasing and may reach a dangerous level endangering the lives of many living organisms. Temperature changes on the earth surface take place due to the exchange of energy. Evaporation of water cools the surrounding areas and brings down the temperature. On the other hand, when the condensation process begins, energy release takes place which increases the temperature. This release and absorption of energy are collectively called as energy exchange. It decides the climate of an area or a region. Thus, the water cycle plays a very important role and becomes the deciding factor of climate.

  • It helps in the purification process-
    Water on the surface of the earth may not be in its purest form. However, the same unpurified water does not get evaporated from the surface. The water which is getting evaporated as water vapour is in the purest form. The rainfall thus enriches the surface of the earth with pure water. In absence of rain, same unpurified water will remain on earth. Consumption of unpurified and dirty water may not only sicken the many living organisms but may also endanger them to a large extent. Also, when condensation takes place and water vapour falls on the earth surface in the form of rain, it free flows and joins oceans. Some of it enters the underground and become groundwater. When water and ice move across the surface or beyond it, they carry along with them essential minerals and replenish the soil. Also, to some extent, rainfall and snowfall are responsible for reshaping of earth's features through sedimentation and erosion of soil.

  • It exerts effects on biogeochemical cycle-
    The hydrologic cycle is a continuous process. This cycle in itself is a continuous biogeochemical process. Water vapour when condenses falls on the earth surface in liquid form which is called as rainfall. This rainwater flows freely over the surface of the earth and even enters inside it to become groundwater. While flowing freely, it carries along with it various minerals, salts, phosphorus and eroded sediment from the surface of the land to deep inside and even mixes them with the rivers, oceans and other water bodies. Since the free flow of rainwater carries salt from the surface of the earth and joins oceans, oceanic water gains its salinity. Also, due to the erosion process, ocean water becomes salty. Water bodies gain nitrogen due to the free flow of water on and below the surface of the earth.


How do humans affect the water cycle?

Lots of activities carried out by humans affect and alter the water cycle. Some of them are mentioned below-

  • Contribution in the scarcity of water-
    We all need water for various purposes and not just to quench our thirst. Our day to day work such as bathing, washing, drinking all requires water. Thus, we keep withdrawing water from the sources. Not only this, we use water for agricultural purposes. We have set up various industries, and they all need water in some amount or the other. Too much withdrawal of underground water decreases the level of groundwater and alters the water cycle. The more the amount of water we withdraw on daily basis, more alterations we are causing with the water cycle.

  • Dam construction-
    Free flow of rainwater will help it to join rivers and oceans. Some amount enters the ground. By confining it in dams, we are preventing it from joining water bodies. Consequently, rivers and lakes dry up. Also, the level of underground water deteriorates. Plants and trees contribute to the water cycle by absorbing groundwater and evaporating it in the form of water vapour. If they cannot find enough underground water, they dry up. Consequently, water cycle alters. Drying of water bodies decreases the evaporation process which also alters the water cycle.

  • Urbanization-
    Urbanization, directly and indirectly, alters the water cycle. For construction purposes, we are using more and more land which means the free flow of rainwater is restricted. Consequently, water cycle alters and groundwater level decreases. Urbanization means deforestation and aforestation. When lots of trees and vegetation are chopped to clear land for construction purposes, it is for sure that we are interfering with the water cycle. It is because vegetation also plays an important role in the water cycle by evaporating water vapour through the transpiration process.


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