The water cycle describes the continuous movement of water on, above, and below the surface of the Earth. The sun heats water which evaporates as vapor into the air. Water vapor condenses into liquid water that falls as precipitation. Precipitation that does not soak into the ground becomes runoff that flows into bodies of water, completing the cycle as that water evaporates again.

1. The Water Cycle

2. The Water Cycle
Evaporation
Sun heats water
Liquid water changes
to gas (vapor)
Water vapor rises
with warm air

3. Humidity
Warm Air Cold Air
 Amount of water
vapor, or moisture in
the air
 Changes with
temperature
 Warm air holds more
moisture than cold
air

4. Measuring Humidity
 Hygrometer is used to
measure the amount
of water vapor in the
air.

5. The Water Cycle
Condensation
 Water vapor cools
 Tiny water droplets
or ice crystals form
 Get bigger and
heavier

6. The Water Cycle
Precipitation
 Air can’t hold up
heavy water
droplets or ice
crystals
 They begin to fall

7. The Water Cycle
 All the different forms of water that
fall from the sky.

8. Precipitation
The air temperature determines the form of
precipitation.

9. Types of Precipitation
Rain
 Liquid
 Air temperature above 32 degrees Fahrenheit
Snow
 Solid
 Air temperature below 32 degrees Fahrenheit
Hail
 Solid
 Formed in clouds
 Winds carry frozen drops higher
 Layers of ice are added
 Repeats
Sleet
 Mixture
 Air temperature just above freezing

10. Measuring Precipitation
Rain gauge
 Open container that
collects precipitation
 Scale on side of
container shows how
much has fallen

11. The Water Cycle
Runoff
 Water that does not
soak into the ground
 Runs downhill into
puddles, streams, rivers,
or lakes
 Then the whole cycle
begins again

12. Review of the Water Cycle