Water Cycle

Also known as Hydraulic Cycle

Earth's water is always in movement, and the natural water cycle, also known as the hydrological cycle, describes the continuous movement of water on, above, and below the surface of the Earth. You may think that every drop of rain that falls from the sky is brand new, but it has always been here and is a part of the water cycle. For millions of years, water is shifting states between liquid, vapour, and ice.

Let's understand the water cycle in simple terms:

  • The heat of the sun provides energy to make the water cycle work.

  • The sun evaporates water from the oceans into water vapor.

  • This invisible vapor rises into the atmosphere, where the air is colder.

  • The colder air causes water vapor to condense into water droplets and clouds.

  • Volcanoes can produce steam, which forms clouds.

  • In the atmosphere, air currents move clouds all around the Earth.

  • Water drops form in clouds, which then fall to Earth as precipitation (rain and snow).

  • In cold climates, precipitation builds up as snow, ice, and glaciers.

  • Snow can melt, becoming runoff, which flows into rivers, the oceans, and into the ground.

  • Some ice evaporates directly into the air, skipping the melting phase (sublimation).

  • Rainfall on land flows downhill as runoff, providing water to lakes, rivers, and the oceans.

  • Some rain soaks into the ground, as infiltration, and, if deep enough, becomes groundwater.

  • Water from lakes and rivers can seep into the ground.

  • Water moves underground because of gravity and pressure.

  • Groundwater close to the land surface is taken up by plants.

  • Some groundwater seeps into rivers and lakes, and can flow to the surface as springs.

  • Plants take up groundwater and evapotranspire, or evaporate, it from their leaves.

  • Some groundwater goes very deep into the ground and stays there for a long time.

  • Groundwater flows into the oceans, keeping the water cycle going.

Components of Water Cycle

Condensation

Condensation is the process by which water vapour in the air is changed into liquid water. Condensation is crucial to the water cycle because it is responsible for the formation of clouds. Condensation is opposite of Evaporation.

Evaporation

Evaporation is the process by which water changes from a liquid to a gas or vapour. Evaporation is the primary pathway that water moves from the liquid state back into the water cycle as atmospheric water vapour. Studies have shown that the oceans, seas, lakes, and rivers provide nearly 90 percent of the moisture in the atmosphere via evaporation, with the remaining 10 percent being contributed by plant transpiration.

Evapotranspiration

Evapotranspiration is the sum of evaporation from the land surface plus transpiration from plants.

Percipitation

Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. It is the primary connection in the water cycle that provides for the delivery of atmospheric water to the Earth. Most precipitation falls as rain.

Infilteration

It is the process by which water present on ground soaks into subsurface soils and moves into rocks beneath through cracks and pore spaces.

Sublimation

Sublimation is the conversion directly from the solid matter into gaseous matter, with no intermediate liquid stage. Sublimation is most often used to describe the process of snow and ice changing into water vapour in the air without first melting into water.

The opposite of sublimation is deposition, where water vapour changes directly into ice - such a snowflakes and frost.


Source: USGS