The Water Cycle
Introduction
Precipitation, evaporation,
and transpiration are all terms that sound familiar, yet may not mean much
to you. They are all part of the water cycle, a complex process that not
only gives us water to drink, fish to eat, but also weather patterns that
help grow our crops.
| Water is an integral part of life on this planet. It is an odorless, tasteless, substance that covers more than three-fourths of the Earth's surface. Most of the water on Earth, 97% to be exact, is salt water found in the oceans. We can not drink salt water or use it for crops because of the salt content. We can remove salt from ocean water, but the process is very expensive. |
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Water is an integral part of life on this planet. It is an odorless, tasteless, substance that covers more than three-fourths of the Earth's surface. Most of the water on Earth, 97% to be exact, is salt water found in the oceans. We can not drink salt water or use it for crops because of the salt content. We can remove salt from ocean water, but the process is very expensive.
The amount of fresh water
on earth is only 3%. Two percent is in solid form, found in ice caps and
glaciers. Because it is frozen and so far away, the fresh water in ice
caps is not available for use by people or plants. That leaves about 1%
of all the Earth's water in a form useable to humans. This fresh water
is found in lakes, rivers, streams, ponds, and in the ground. (A small
amount of water is found as vapor in the atmosphere.)
Scientific Concepts
There are six important processes that make up the water cycle. These are:
Evaporation
Evaporation is the process
where a liquid, in this case water, changes from its liquid state to a
gaseous state. Liquid water becomes water vapor. Although lower air pressure
helps promote evaporation, temperature is the primary factor. For example,
all of the water in a pot left on a table will eventually evaporate. It
may take several weeks. But, if that same pot of water is put on a stove
and brought to a boiling temperature, the water will evaporate more quickly.
| During the water cycle some of the water in the oceans and freshwater bodies, such as lakes and rivers, is warmed by the sun and evaporates. During the process of evaporation, impurities in the water are left behind. As a result, the water that goes into the atmosphere is cleaner than it was on Earth. |
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Condensation is the opposite of evaporation. Condensation occurs when a gas is changed into a liquid. Condensation occurs when the temperature of the vapor decreases.
When the water droplets
formed from condensation are very small, they remain suspended in the atmosphere.
These millions of droplets of suspended water form clouds in the sky or
fog at ground level. Water condenses into droplets only when there are
small dust particles present around which the droplet can form.
Precipitation
When the temperature and
atmospheric pressure are right, the small droplets of water in clouds form
larger droplets and precipitation occurs. The raindrops fall to Earth.
As a result of evaporation,
condensation and precipitation, water travels from the surface of the Earth
goes into the atmosphere, and returns to Earth again.
Surface Runoff
Much of the water that
returns to Earth as precipitation runs off the surface of the land, and
flows down hill into streams, rivers, ponds and lakes. Small streams flow
into larger streams, then into rivers, and eventually the water flows into
the ocean.
Surface runoff is an
important part of the water cycle because, through surface runoff, much
of the water returns again to the oceans, where a great deal of evaporation
occurs.
Infiltration
Infiltration is an important process where rain water soaks into the ground, through the soil and underlying rock layers. Some of this water ultimately returns to the surface at springs or in low spots downhill. Some of the water remains underground and is called groundwater.
As the water infiltrates
through the soil and rock layers, many of the impurities in the water are
filtered out. This filtering process helps clean the water.
Transpiration:
One final process is important
in the water cycle. As plants absorb water from the soil, the water moves
from the roots through the stems to the leaves. Once the water reaches
the leaves, some of it evaporates from the leaves, adding to the amount
of water vapor in the air. This process of evaporation through plant leaves
is
called transpiration. In large forests, an enormous amount of water will
transpire through leaves.
The Cycle
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Each part of the cycle drives the other parts. Water is constantly being cycled between the atmosphere, the ocean and land. This cycling is a very important process that helps sustain life on Earth. |
Water's state (solid,
liquid or gas) is determined mostly by temperature. Although water continuously
changes states from solid to liquid to gas, the amount of water on Earth
remains constant. There is as much water now as there was hundreds of millions
of years ago.
Cloud Formation
Precipitation is one key
to the water cycle.
Rain comes from clouds,
but where do clouds come from?
Through the process of evaporation and transpiration, water moves into the atmosphere. Water vapors then join with dust particles to create clouds. Eventually, water returns to Earth as precipitation in the form of rain, snow, sleet, and hail.
All clouds contain water vapors. You rarely ever see clouds in the desert because there is very little water to evaporate and form clouds. Coastal regions can receive a lot of rain because they pull up moisture from surrounding waters.
Cloud size is influenced
by many complex factors, some of which we still do not understand very
well. These include: heat, seasons, mountain ranges, bodies of water, volcanic
eruptions, and even global warming.
There are many funny names
for clouds.
Have you ever wondered
why clouds have such weird names?
In 1802 an Englishman by the name of Luke Howard invented the cloud naming system that is still in use today. Howard used Latin names to describe clouds. (The first part of a cloud's name describes height, the second part shape.)
The prefixes denoting
heights are:
cirro,
high clouds above 20,000 feet,
alto
and mid level clouds between 6,000 - 20,000 feet.
There is no prefix for
low
level clouds.
The names denoting shapes
are:
cirrus
means curly or fibrous,
stratus
means layered
cumulus
means lumpy or piled.
Nimbo or nimbus is added to indicate that a cloud can produce precipitation.
Given that information, describe what each of the following clouds would look and act like?
•Cumulonimbus
•Nimbostratus
•Cirrocumulus
•Altostratus
Material courtesy of Copyright © 1995-8 The Evergreen Project,
Inc.
http://mbgnet.mobot.org/fresh/cycle/index.htm
