Transcript The Water Cycle - Hrsbstaff.ednet.ns.ca

The Water Cycle
 The amount of water on Earth is finite
(which means that there is a limited
amount).
 All of the water present at the beginning of
time is still present now!
 All water on Earth is constantly
moving.
 The natural water cycle, also known as the
Hydrologic cycle, describes the continuous
movement of water on, above, and below
the surface of the Earth.
 The water cycle is self-renewing and constant.
 The Sun provides the energy to power the water
cycle.
 Water is always changing states between liquid,
vapor (gas), and ice.
 These processes happen in the blink of an eye
and over millions of years.
The Water Cycle Process
 The water cycle collects, purifies, and redistributes
the Earth’s water.
 The sun heats up the bodies of
water it is shining on.
 The heat causes some of the water to change
from a liquid state to a gaseous state, this is called
evaporation.
Evaporation
 Only pure water evaporates.
 Fact This is the reason why the ocean stays
salty! Pure water evaporates leaving the salt
behind.
 Water also evaporates from the upper layer of soil
and from plants. Evaporation from plants is called
transpiration (it like plants sweating!)
Evaporation/Transpiration
 The rate of evaporation depends on a
number of factors:
– Air temperature: Evaporation is much higher in
warmer climates than in colder climates.
– Amount of moisture in the air: Evaporation
rates are lower in humid areas than in dry areas
because humid air has little room to hold
additional water.
Condensation
 As evaporated water rises into the sky,
temperatures cool and it collects around particles
of pollution and dust to form larger droplets.
 The process where water vapour (gas) in the air
turns into liquid water is condensation.
 Condensation helps in the formation of clouds.
Condensation
 Warmer air is able to hold more water than
cold air because there is more energy in
warm air molecules.
 Dew Point: The temperature at which
condensation occurs. Happens when warm
air masses holding a lot of water cool.
Cloud Formation
 As air rises the temperature cools, and the ability
to hold water decreases.
 Once moist air has reached the dew point
elevation clouds are formed.
 Water vapour needs to have a surface to
condense on. In the atmosphere the water vapour
condenses on dust particles to form clouds.
Precipitation
 Precipitation occurs when moist air in the
atmosphere rises above the dew point.
 This occurs in one of 3 ways:
– Convectional precipitation
– Orographic precipitation
– Frontal precipitation
Convectional Precipitation
 As air rises it loses the ability to hold on to the
water.
 Convection currents in the atmosphere carry water
vapour higher in a steady state of vertical air flow.
 These currents only occur when there is hot air,
thus they often occur in Canada in the summer in
the form of thunderstorms.
Orographic Precipitation
 In Ororgraphic, or relief precipitation, air is also
forced to rise above the dew point, however it is
not hot air that causes this but rather a change in
surface elevation.
 This often occurs in mountainous regions. As air
continues up the mountain more and more
moisture is released. By the time the air has
reached its highest point there the air has lost
most of its moisture.
Frontal Precipitation
 Frontal precipitation occurs when two air
masses with different characteristics meet.
 Denser air masses push the air higher until
the dew point is reached.
Runoff
 Excessive rain or snowmelt can produce
overland flow to creeks and ditches.
 Runoff is visible flow of water in rivers,
creeks and lakes as the water stored in the
basin drains out.
 If water lands on the ground and is unable to
penetrate, it becomes surface runoff.
Percolation
 Some of the precipitation and snow melts
and moves downwards, percolates (filters)
or infiltrates through cracks, joints and
pores in soil and rocks until it reaches the
water table where it becomes groundwater.
Groundwater
 Subterranean water is held in cracks and
pore spaces.
 Depending on the geology, the groundwater
can flow to support streams. It can also be
tapped by wells.
 Some groundwater is very old and may
have been there for thousands of years.
Groundwater Layers
 The layer where groundwater flows
downward is the unsaturated zone.
 The layer where water accumulates is called
the saturated zone.
 The level between the saturated and the
unsaturated zone is called the water table.
Aquifiers
 Some surface seep into the ground where it
is held between particles of soil as
groundwater or deep beneath the surface in
porous layers called aquifers.
Water Story Assignment
 Imagine yourself as a tiny drop of water; what would your
life be like?
 Create an adventure story about your life as a drop of
water. Where would you travel? How would you get
there?
 You must include the various parts of the water cycle and
explain what happens to you as the drop of water as you
travel through each of the different phases of the water
cycle.
 This activity should demonstrate a clear understanding of
the water cycle!
The Three Gorges Dam
 Read “The Three Gorges Dam” case study
on pages 164 – 165 in the text book.
 Answer questions:
– 1 – 4, page 165
– 8 page 169
– 11 a, c page 169
Water Poster Assignment
 Create a poster depicting the path of water
through the Water Cycle.
 Be sure to include the various stages of water
throughout the water cycle.
 All parts of the water cycle should be included
(evaporation, transpiration, condensation, etc.)
 Be creative! The poster should be neat, easy to
read, organized and colourful. Remember it is a
cycle, so it should flow that way!