Transcript The Water Cycle - Home

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