The Water Cycle

The Water Cycle (Hydrological Cycle)

Seas and oceans contain 97% of the world’s water.

2% of water is frozen in ice.

That means that only 1% of the world’s fresh water is in the land/air.

This water is recycled repeatedly in the water cycle or the hydrological cycle

There are a number of steps in this cycle

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Evaporation – Evaporation is when the sun heats up water in rivers or lakes or the ocean and turns it into vapor or steam. The water vapor or steam leaves the river, lake or ocean and goes into the air

Transpiration – the process by which plants lose water out of their leaves.  Transpiration gives evaporation a bit of a hand in getting the water vapor back up into the air.

Condensation – Water vapor in the air gets cold and changes back into liquid, forming clouds. This is called condensation.

Precipitation – Precipitation occurs when so much water has condensed that the air cannot hold it anymore.  The clouds get heavy and water falls back to the earth in the form of rain, hail, sleet or snow.

Collection – When water falls back to earth as precipitation, it may fall back in the oceans, lakes or rivers or it may end up on land.  When it ends up on land, it will either soak into the earth and become part of the “ground water” that plants and animals use to drink or it may run over the soil and collect in the oceans, lakes or rivers where the cycle starts

Percolation – The downward movement of water through openings in soil or rocks

Groundwater – Some of the water from precipitation will soak into the soil and rocks as groundwater. A varying proportion of groundwater stays in the shallow soil layer, and will move slowly towards streams and rivers. When groundwater soaks deeper into the soil it refills the underground aquifers, where it can stay for long periods of time or be used by humans through drilling wells into aquifers.

Through flow – The movement of water horizontally beneath the land surface, usually when the soil is completely saturated.

Infiltration – The movement of water into soil layers

Surface Run Off – Surface run off is the precipitation that falls on land and flows downhill towards stream channels which join rivers and eventually reach the oceans. Only about one third of precipitation falling on land will return to rivers and oceans. The rest will be soaked into the soil as groundwater, evaporated or transpired.

Precipitation – Rain, snow, sleet or hail

Aquifer – An aquifer is a layer of water soaked sand, soil, stone, silt or clay underground. Aquifers act as huge underground water storage systems which people all over the world rely on for fresh water.

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