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.  

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.
Condensation

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
 
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. 
As the water evaporates, vapors rise and condense into clouds. The clouds move over the land, and precipitation falls in the form of rain, ice or snow. The water fills streams and rivers, and eventually flows back into the oceans where evaporation starts the process anew.  Learn a lot more about this complicated process in concepts.
 

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

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