The Water Cycle
May 2013
The Water Cycle
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There are 5 processes at work in the water
cycle.
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Condensation
Precipitation
Infiltration
Runoff
Evapotranspiration
These occur simultaneously and continuously
with the exception of precipitation.
The Water Cycle
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Water vapour condenses and forms clouds. =
precipitation in suitable conditions.
Precipitation infiltrates the soil or flows into
the ocean as runoff.
Surface water evaporates which returns
moisture to the atmosphere.
Plants return water to the atmosphere by
transpiration.
Condensation
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This is process of water changing from a
vapour to a liquid.
Water vapour in the air rises mostly by
convection.
As the warmer air rises, the water vapour will
lose energy causing its temperature to drop.
This allows the water to change state to a
liquid or ice.
Precipitation
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Precipitation is water being released from
clouds as rain, sleet, hail, etc.
Begins after water vapour becomes to heavy
to remain in the atmospheric air and falls.
Sometimes precipitation will evaporate before
it hits the ground, but for the most part it
reaches the Earth’s surface and adds to the
Earth’s surface water.
Infiltration
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A portion of the precipitation that reaches the Earth’s
surface seeps into the ground via infiltration.
The amount of water that infiltrates the soil varies
with the degree of land slope, the amount and type
of vegetation, soil type and rock type, and whether
the soil is already saturated by the water.
The more openings in the surface, the more
infiltration.
Water that doesn’t infiltrate is labelled as run off.
Runoff
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Precipitation that does not infiltrate the
Earth’s surface, is called runoff.
Runoff can also come from melted snow
and ice.
When there is a lot of precipitation,
soils become saturated with water and
new rainfall is unable to infiltrate it.
This new rainfall will become runoff.
Evapotranspiration
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Evapotranspiration is water evaporating from the
ground and transpiration by plants.
This is also the way water vapour re-enters the
atmosphere.