Water cycle or hydrological cycle is the continuous movement of water on earth. In this process, water moves from one reservoir to another by processes such as evaporation, sublimation, transpiration, condensation, precipitation, surface runoff and infiltration, during which water converts itself to various forms like liquid, solid and vapour.
Evaporation is a type of vaporization, where liquid is converted to gas before reaching its boiling point. Water evaporates from the surface of the earth and water bodies such as the oceans, seas, lakes, ponds and rivers.
Sublimation is conversion of solid to gas, without passing through the intermediate liquid phase. Ice sheets and ice caps from north and south poles, and icecaps on mountains, get converted into water vapour directly, without converting into liquid.
Transpiration is the process by which plants release water vapour into the atmosphere through stomata in leaves and stems.
Condensation is the changing of gas phase into liquid phase and is the reverse of vaporisation. At higher altitudes, the temperature is low. The water vapour present there condenses to form very tiny particles of water droplets. These particles come close together to form clouds and fog.
Due to change in wind or temperature, clouds combine to make bigger droplets, and pour down as precipitation (rain). Precipitation includes drizzle, rain, snow and hail.
As the water pours down, it runs over the surface of earth. Runoff water combines to form channels, rivers, lakes and ends up into seas and oceans.
Some of the precipitated water moves deep into the soil. Then it moves down and increase the ground water level.
Some of the precipitated water flows through soil and porous or fractured rock.
Infiltration and percolation are two related but different processes describing the movement of water through soil.
Human impacts on water cycle
Major human activities affecting the water cycle on land are urbanisation, dumping of plastic waste on land and into water, polluting water bodies and deforestation.
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