Download Water Cycle

The cycle starts when the sun's heat provides
energy to evaporate water from the surface.
Then, winds lift the water vapor from the ocean
over the lands into the atmosphere. The water
vapor condenses to form clouds, and when the
conditions are just right, the clouds release water
as rain or snow. About 80% of the rain falls in the
oceans, but the rest falls onto land. Rivers and
streams collect water from the ground and return
it to the ocean so the whole cycle can start all
over again. The water cycle never ends because
the salty ocean water constantly supplies fresh
water to the continents.
One process which tranfers water from the ground back
to the atmosphere is evaporation. Evaporation is when
water passes from a liquid phase to a gas phase. Rates
of evaporation of water depend on factors such as solar
radiation, the temperature, humidity, and wind.
Water that is held in lakes and rivers evaporates directly
into the atmosphere, but some of the water in the groung
may also be returned to the atmosphere by way of
evaporation through the
soil surface. Of course,
the ocean is the greatest
source for water
evaporated into the
atmosphere.
Condensation is the change of water from its gaseous form
(water vapor) into liquid water. Condensation generally
occurs in the atmosphere when warm air rises, cools and
looses its capacity to hold water vapor. As a result, excess
water vapor condenses to form cloud droplets.
Precipitation is the main way for transporting water from
the atmosphere to the surface of the earth. There are
several forms of precipitation, the most common of which
for the United States is rain. Other forms of precipitation
include; hail, snow, sleet, and freezing rain.
Groundwater is all the water that has gone through the
earth's surface and is found in one of two soil layers. The
one nearest the surface is the "zone of aeration", where
gaps between soil are filled with both air and water. Below
this layer is the "zone of saturation", where the gaps are
filled with water.
Transpiration is the process by which plants return
water to the atmosphere. After absorbing water from
the ground, plants release water through their leaves.
Transpiration helps plants stay cool, in the same way
perspiration keeps humans and animals cool.
Runoff is the movement of land water to the oceans, mostly
in the form of rivers, lakes, and streams. Runoff consists of
precipitation that hasn’t evaporated, transpired or
penetrated the surface to become groundwater. Even the
smallest streams are connected to larger rivers that carry
billions of gallons of water into oceans worldwide.