NCERT Notes: The Hydrologic Cycle [Geography Notes For UPSC]

The hydrological cycle is also known as the “water cycle”; it is the normal water recycling system on Earth.  It is the sum total of all processes in which water moves from the land and ocean surface to the atmosphere and back in form of precipitation.

Every year March 22 is observed as World Water Day and UPSC aspirants can know more about the same at the linked article.

Get NCERT notes on important topics for the IAS aspirants. These notes will also be useful for other competitive exams like banking PO, SSC, state civil services exams and so on. This article talks about the Hydrological cycle.

Aspirants preparing for the upcoming UPSC examination can go through the relevant links provided below for preparation even better –

Water Cycle Explanation

What is Water?

  • Water is a cyclic resource as it is used and re-used.
  • About 71% of the planetary water is found in the oceans.
  • The remaining is held as freshwater in glaciers and ice caps, groundwater sources, lakes, soil moisture, atmosphere, streams and within life.
  • About 59% of the water on the land surface evaporates and returns back to the atmosphere.
  • The remaining run-off on the surface penetrates into the ground or a part of it becomes glaciers.

Water Cycle (UPSC Notes):- Download PDF Here

Distribution of water on the surface of the earth

Reservoir Percentage of the total Volume in Million Cubic km
Oceans 97.25 1,370
Ice caps and glaciers 2.05 29
Groundwater 0.68 9.5
Lakes 0.01 0.125
Soil moisture 0.005 0.065
Atmosphere 0.001 0.013
Streams and Rivers 0.0001 0.0017
Biosphere 0.00004 0.0006

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Hydrological Cycle Diagram

Hydrological cycle / Water Cycle

Hydrological Cycle

  • The hydrological cycle is the circulation of water within the hydrosphere of Earth in different forms such as liquid, solid and gaseous states.
  • It also denotes the uninterrupted exchange of water between the land surface, oceans and subsurface and the organisms.
  • The hydrologic cycle begins with the evaporation of water from the surface of the ocean.

Hydrological Cycle Processes – Components and Processes of the Water Cycle

Components Processes
Water storage in oceans Evaporation



Water in the atmosphere Condensation


Water storage in ice and snow Snowmelt runoff to streams
Surface runoff Streamflow freshwater storage infiltration
Groundwater storage Groundwater discharge springs

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What is Evaporation?

  • The conversion of water from liquid to gas stage as it moves from the ground or bodies of water into the atmosphere.
  • The source of energy for evaporation is mainly solar radiation.

Get NCERT Notes on Evaporation And Condensation at the linked article for UPSC preparation.

What is Transpiration?

  • Water vapour is also discharged from plant leaves by a process called transpiration.

What is Sublimation?

  • The process in which solid water such as snow or ice directly changes into water vapour.

What is Condensation?

  • The transformation of water vapour to liquid water droplets in the air, forming fog and clouds.

What is Precipitation?

  • The condensed water vapour falling to the surface of the Earth is known as Precipitation.
  • It occurs in the form of rain, snow, and hail.

What is Runoff?

  • Runoff is a visible flow of water in rivers, creeks, and lakes as the water stored in the basin drain out.

What is Snowmelt?

  • The runoff created by melting snow.

What is Percolation?

  • Water flows vertically through the soil and rocks under the effect of gravity.

Water Cycle (UPSC Notes):- Download PDF Here

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