The Water Cycle - Home
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The Water Cycle
The Earth has a limited
amount of water
The water on Earth
moves from the Earth
to the sky and back to
the Earth in a cycle.
This is called the water
cycle
Steps of the Water Cycle
1. Evaporation
2. Condensation
3. Precipitation
4. Collection
The Cause of Phase Changes in Water Cycle
Kinetic Theory: All atoms and molecules move
When energy (thermal) is added, atoms move
faster
Atoms and Molecules are naturally attracted to one
another
They want to form bonds
However, when enough energy is added to
these atoms, the bonds they form aren’t strong
enough to hold them together
When this happens, the atoms undergo a phase
change
Phase Changes
Solid= little energy added,
molecules stay together
Liquid= more energy added,
molecules bond and break bonds
Gas=too much energy,
molecules can’t keep bonds
1) Evaporation
Evaporation: process of
turning liquid into gas.
Water (H2O) : thermal
energy added to liquid
water in lakes, rivers,
oceans by radiation
from sun and turns into
a gas (water vapor)
In water cycle, the step
where H2O enters the
atmosphere
Remember!!!
When a gas is heated, the molecules will speed up
As they speed up, they occupy more space and thus become lighter and
unable to form bonds
Lighter (hotter) gases tend to rise
“Hot Air Rises” Principle
2) Condensation
Condensation: process of
turning gas into liquid
Thermal energy is
removed and water
molecules begin forming
bonds
Causes formation of
clouds
Remember!!!
When a gas is cooled, the molecules
will slow down
As they slow down, they occupy less
space and thus become heavier and
able to form bonds
Heavier (colder) gas tend to sink
“Hot Air Rises” Principle
How to Clouds Form?
The amount of water vapor in the atmosphere is called relative
humidity.
As temperature and pressure go down, molecules lose heat
energy, they slow down and go from gas (vapor) to liquid
When this occurs, the water vapor has reached its Dew
Point: temperature at which the water vapor begins to form
liquid water
In the atmosphere, the little droplets of water form clouds by
sticking to particles in the air called condensation nuclei (ex.
dust, smoke, salt)
What happens if you increase temperature and pressure?
3) Precipitation
Precipitation: tiny
water droplets combine
to form bigger droplets
that the atmosphere
can’t hold, so the water
falls
Examples: rain, snow,
sleet, and hail
4) Collection/Runoff
When water falls back
to earth as
precipitation, it may
fall back in the oceans,
lakes or rivers or it
may end up on the land
surface
Quiz Time!
During which water cycle step does H2O enter the atmosphere?
a) Evaporation
b) Condensation
c) Precipitation
d) Transportation
How does H2O return to Earth’s surface from the atmosphere?
a) Evaporation
b) Condensation
c) Precipitation
d) Transportation
Quiz Time!
Which step of the water cycle
is represented by letter B?
a) Evaporation
b) Condensation
c) Precipitation
d) Transportation
Erosion
Erosion: Loss of topsoil
Agents:
Water (rivers, floods, glaciers)
Wind
Gravity
Effects of Erosion:
Loss of farmland (fertile soil)
Destruction of property (landslides)
Negative impact on wildlife (fish, plants)
Rate of erosion: how quickly erosion occurs
Factors Affecting Rate of Erosion
Soil erosion increases with:
Smaller soil particles that are loosely
compacted
Sand vs. Soil
Areas with less vegetation
Roots hold onto soil preventing erosion
Clear cutting, tree thinning, or fires
increase erosion
Areas with steep slopes (Gravity)
What area has the least
erosion?
Areas that are flat with heavy
vegetation experience little
erosion
Types of Water
Surface Water
Ground Water
Local Water
Surface Water
Water that sits or flows
above the earth
Including lakes,
oceans, rivers, and
streams.
Ground Water
Water that flows or
seeps downward
and accumulates in
the ground
Supplies springs
and wells.
The point where
water begins to
collect is called the
water table
Local Water
Rural (country) areas
have a shortage due
to falling water table
Phoenix & Tucson
Currently: water is
abundant due to CAP
Future: Water
shortages due to
growth
Water Issues
How Much Water Is There?
3 Factors that Affect Water Quantity
1) Population Growth
More people create greater demands for water
2) Precipitation Levels
3) Drought
“Water is the true wealth in a dry land" --Wallace
Stegner
Water resources become less dependable
Water bodies become depleted
Reservoirs are low
3 Factors that Affect Water
Quality
1) Acid Rain
2) Agriculture
3) Factories and Chemical Pollutants
1) Acid Rain
When fossil fuels are burned, sulfur and nitrogen
gases are released into the air
These pollutants chemically combine with water
forming sulfuric acid and nitric acids
Effects of Acid Rain
Damages Plants, Animals, and Buildings
2) Agriculture
Crops and Cows
Chemical fertilizers and animal manure runs
off and is washed into ponds, rivers, &
groundwater
Crops: Fertilizers
Rich in nutrients (Nitrogen, Phosphorus,
Potassium) which increase algae growth
when entering the water supply
When algae dies, bacteria decompose dead
material and use up oxygen in water
causing other organisms (fish, plant life) to
die
2) Agriculture
Cows: Manure
Manure (poop) carries
bacteria into the water
supply which multiply
and use up the oxygen
in the water
3) Factories and Chemical Pollutants
Factories: Metals from
mining & gasoline
refineries
Homes: Detergents,
cleaning products
Highway Runoff: fuels, oil
Water Management: Dams and
Reservoirs
Provide water storage for
run-off
Dams & reservoirs along
Salt and Verde Rivers
supply irrigation &
drinking water for metro
Phoenix area
Disrupts river system
Tapping Groundwater
Using ground water
drops the water table
This leads to water
shortages
This also leads to
contaminations from
pesticides and fertilizers
Ground Water Contamination
Treated Wastewater
Treated wastewater - sewage, industrial
wastewater, or other effluent that is
treated to a level necessary for its
intended usage.
Used to –
Irrigate golf courses, lawns
Cool power plants
Irrigate crops