The Water Cycle
Chapter 5 Notes
Chapter Preview: Earth’s surface is mostly covered with water, yet only 1% of it is drinkable. That amount
would soon be used up were not for the water cycle, the natural sequence by which surface water evaporates,
condenses, and falls again. There are 4 basic cloud types, each of which forms under specific conditions.
Precipitation, in the form of rain, snow, sleet, or hail, falls from clouds and is a central part of the water cycle.
Most of Earth’s water is in the oceans. The oceans affect climate, cloud and fog formation, and temperatures
near the coasts.
Lesson 1: The Water Cycle

Less than 1% of Earth’s water supply is usable fresh water. The rest is deep underground or is found as
ice in glaciers and ice caps.

The water cycle is a pattern by which water evaporates, rises, forms clouds, condenses into drops, falls,
soaks into the ground, and runs back into bodies of water again.

Water is cleaned and renewed in the processes that make up the water cycle.

Water exists in three states liquid water, solid ice, and a gas called water vapor. Water changes from
one state to another in processes that make up the water cycle.

When precipitation (rain, hail, sleet, or snow) falls on land, groundwater soaks into the ground and
collects in the open spaces between soil and rock.

Runoff flows downhill without sinking into the land.

Runoff also causes erosion. When runoff flows over land, the water often picks up pieces of land and
carries them along.

Runoff can also pick up trash and harmful chemicals. This is how our water gets polluted.
Lesson 2: Precipitation

The Sun warms the Earth’s surface. The warm air is lighter (less dense) than cold air so the warm air
rises. Temperatures are much cooler above the Earth’s surface so as the warm rises and meets the
cooler above, it cools. Since the cold air is heavier (denser) it sinks back to the ground. This process is
called CONVECTION.

As moist air rises, water vapor condenses and clouds can form.

Clouds are made up of tiny droplets of liquid water or ice.

Clouds form and release precipitation as rain, snow, sleet, and hail.

There are four basic types of clouds: cirrus, stratus, cumulus, and cumulonimbus.

Cirrus Clouds are high feathery clouds. They are up so high they are actually made of ice particles. They
are indicators of fair weather when they are scattered in a clear blue sky.

Stratus Clouds They look like flat sheets of clouds that form at low levels. These clouds can mean an
overcast day or steady rain. They may stay in one place for several days.

Cumulus Clouds are the puffy clouds that look like puffs of cotton. Cumulus clouds that do not get very
tall are indicators of fair weather. If they do grow tall, they can turn into thunderstorms. The bottoms
of cumulus clouds are fairly close to the ground.

Cumulonimbus Clouds bring heavy rain or thunderstorms. They may extent up through the
troposphere.

Fog is a type of cloud that forms when moist air near the ground becomes cool enough for water vapor
to condense, forming water droplets.

Types of precipitation:
o Rain: Drops of liquid water. Rain can begin as liquid water and hit the ground as liquid water,
or rain can begin as ice crystals that melt and hit the ground as liquid water.
o Sleet: Begins as small drops of rain. When the rain drop falls through a layer of air that is colder
than the water’s freezing point, they freeze into tiny ice pellets.
o Snow: Small flakes and pellets of ice. Snowflakes are produced when the temperature in a
cloud is cold enough for water vapor to form ice crystals.
o Hail: made up of round chunks of ice called hailstones. They form when droplets of rain freeze
inside a cloud with strong updraft winds, such as a large cumulonimbus cloud. Strong winds can
lift the hailstone through the inside of the cloud. A hail stone may rise and fall several times.
Each time the hail stone will gain a new icy coat. Finally when it’s heavy enough, it will hit the
ground. Some hail stones can be large enough to dent cars and cause damage. Dinner table
conversation: Share your experiences with hail. When did you last see hail, and what did it look
like?

Humidity is the amount of water vapor in the air at any given time. Our hermit crabs in the classroom
need a humid environment in their enclosure. How do we create humidity for our crabbies?

Warm air can hold more water vapor than cold air. Predict: Do you think there is a lot of humidity in
the Polar Regions?

50% humidity means the air is holding half as much water vapor as it could hold at that temperature.

100% humidity means that “That’s all the humidity that the air can hold and it can’t hold no more!”
Improper English, but I’m kind of quoting Popeye. He’s an old cartoon character that when provoked
by his rival Brutus used to say, “That’s all I can stand and I can’t stand no more.” Then he’d eat his can
of spinach and beat up Brutus---priceless!

So, at 100% humidity the air is saturated and has reached its dew point.

If the temperature drops below the dew point, water condenses and fog or clouds form.
Lesson 3: Ocean Effects

Oceans have a major effect on Earth’s weather and climate.

Land and water have different heat capacities.

In general, land heats up faster and reaches higher temperatures than the bodies of water near it.
Have you ever been to the Pacific Ocean on a hot summer day and burned your feet while dancing
(your feet feel like they are on fire) across the sand only to rush to the ocean and dip your toes into
much cooler water?

The Pacific Ocean is cold because of the California Current that flows along the coast.

The Pacific Ocean keeps California’s climate mild.

An ocean current is a moving stream of water in the ocean. Water that flows within that
current has a similar temperature and density.

There are two types of ocean currents: surface currents and deep currents.

Ocean currents are examples of convection currents.

Surface currents move in great circles driven by winds and the effects of the earth’s rotation.

Warm currents move warm ocean water from near the equator toward cooler polar regions.
Cold currents move in the opposite direction. This helps balance temperatures at the earth’s
surface.

Deep ocean currents move vertically (up and down) because of differences in temperature and
salinity (saltiness).

Saltier water is denser (heavier) so it sinks. It flows back toward the equator along the ocean
bottom. Then near the equator the water warms and becomes less salty and less dense. It
returns to the surface to complete the cycle.

Oceans play an important role in the water cycle and have a great affect on climate.

Ocean currents warm and cool the air above them.

Oceans take longer than land to heat up or cool down. An ocean can store the summer’s heat long
into winter.

The oceans slowly release stored energy.