5 elements in the Water Cycle Simplified

The water cycle is The natural cycle of evaporation of water and
subsequent condensation and precipitation as rain and snow, which assure that
the level of water in the environment remains constant. For this balance to be
sustained, different processes take places at different parts of the
environment.

1.      
Aquifers

Much less
obvious than surface water, which we see in streams, lakes, and ponds, is
groundwater, which occurs in aquifers, i.e. permeable, saturated, underground
layers of rock, sand, and gravel. In many areas, groundwater is the most
important reservoir of water. The upper, unconfined portion of the groundwater
constitutes the water table, which flows into streams and is partly accessible
to plants; the lower confined layers are generally out of reach, although they
can be “mined” by humans. The water
table is recharged by water that percolates through the soil from precipitation
as well as by water that seeps downward from ponds, lakes, and streams. The
deep aquifers are recharged very slowly from the water table.

Groundwater
flows much more slowly than surfacewater, anywhere from a few millimetres to a
metre or so per day. Rural areas tend to depend almost exclusively on wells to
access groundwater, and its use is growing at about twice the rate of surface
water use.

2.      
Evaporation

When liquid water changes its state to a gas it forms vapour and the
process is called evaporation. The
water vapour produced by evaporation spreads out through the surrounding air.
All over the Earth’s surface there are large water surfaces from which water
will evaporate. Seas, rivers, lakes and ponds all provide a source of water vapour
in the air through evaporation. Water will also evaporate from moist soils.

It is worth to note that water is a waste product in respiration.
This is excreted from the body as water vapour in exhaled breath. All living
things using aerobic respiration excrete water vapour. The plants transpire, with water vapour being
released from their leaves. These three processes – animal respiration, plant
transpiration, and natural evaporation – are the main sources of water vapour
in the air. Between them, they provide a very variable quantity of air
moisture. How much moisture is in the air depends on:

•         
temperature

•         
the saturation level of the air.

Condensation

When water vapour is cooled, it will condense back to a liquid. Fog, mist and frost are all caused by a
drop in air temperature causing condensation of water vapour. There is a limit
to the amount of water vapour that a given quantity of air will hold. That
limit varies with the temperature of the air. Saturated cold air holds less
water vapour than saturated warm air.

Humidity is a measure of how much water vapour the air is
holding. Dry air has a very low humidity. When the humidity gets very high (at
the saturation level at that temperature) the air cannot hold more water. Under
these conditions, a small fall in the temperature means that the air is
oversaturated. Water condenses out – normally as rain.

Winds blowing across the sea will collect water vapour evaporating from
the surface. When these moist winds meet the land they may be forced to rise.
As they do, they cool with altitude, and rain results. The rain falls on the
ground and drains into rivers. It eventually runs out to sea. This is the basis
of the water cycle.

The rate at which water evaporates from a water surface depends on
temperature and on air movement: the warmer the water, the quicker it will
evaporate. Still air can quickly become saturated; moving air carries the water
vapour away, making saturation far less likely.

The water cycle

 Precipitation

Warm winds blowing over warm seas will become very moist. When they meet
land they may cause very heavy rainfall (the monsoon winds in the tropics, for
example). Cold winds blowing over cool seas will be relatively dry, and produce
much less rainfall than a monsoon wind. If the winds are blowing over land (not
sea), their humidity will depend on how much water is in and on the land. Winds
blowing over the Sahara Desert, for example, are very hot and dry. There is
very little water in the Sahara Desert.

The water cycle summary

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  Breaking the Water Cycle

In dense
forest ecosystems such as tropical rainforests, more than 90% of the moisture
in the ecosystem is taken up by plants and then transpired back into the air.
Because so many plants in a rainforest are doing this, the vegetation is the
primary source of local rainfall. In a very real sense, these plants create
their own rain: the moisture that travels up from the plants into the
atmosphere falls back to earth as rain.

Where forests
are cut down, the organismic water cycle is broken, and moisture is not
returned to the atmosphere. Water drains away from the area to the sea instead
of rising to the clouds and falling again on the forest. As early as the late 1700s,
the great German explorer Alexander von Humbolt reported that stripping the
trees from a tropical rainforest in Colombia prevented water from returning to
the atmosphere and created a semiarid desert.