Music
Title: Water, Water Everywhere
Water is all around us, and it's importance to nearly every process on earth cannot be underestimated.
The process by which water moves around the Earth, from the ocean to the atmosphere to
It is the only compound that can found naturally as a liquid, gas, and solid.
The process by which water moves around the Earth, from the ocean to the atmosphere to
the land, and back to the ocean, is called the water cycle.
Water regulates climate, storing heat during the day and releasing it at night, and
carries heat from the tropics to the poles, by sea and by air.
Let's follow a single molecule of water, beginning in the ocean, through the paths it
might take before eventually winding up right where it started - back in the big blue
sea.
The fuel for this journey will be provided by our planet's prime energy source: the sun.
During the day, the sun heats up the air and ocean surface, causing water molecules to
evaporate.
Evaporation occurs when a liquid molecule of water escapes into the air as a gas.
This scientific visualization shows how water evaporation, indicated in turquoise, is
driven by the energy of the sun.
Notice how the rate of evaporation pulses over land: it speeds up during the day and
almost disappears at night.
Over the ocean, evaporation appears to remain constant, both day and night.
Water in the air in gas form is known as water vapor.
The molecule is now fresh water, having left the ocean salt and other particles behind.
[Paula Bontempi] The water evaporates and goes into the atmosphere, and then it doesn't
necessarily just turn around and fall as rain or snow. [Narrator] Condensation is the
process by which water vapor molecules cool, stick together, and become liquid again in
cloud formation.
This often happens high in the atmosphere where the temperature is much lower than it is
near the surface.
[Paula Bontempi] What happens in the atmosphere is, just like we have currents in the
ocean, we have winds in the atmosphere that actually, to some extent, drive what goes on
in the ocean currents.
Materials in the atmosphere can travel a great distance, sometimes a quarter of a way
around the world, just until they get to the point where they actually turn into rain or
snow and thereby fall back to the ocean or fall back to the land.  This is called
precipitation.
precipitation. If the water molecule falls on the land as snow, it may be stored for a
very long period of time in a polar ice sheet or mountain glacier, depending on climate
conditions.  [Matt Rodell] when rain falls or the snow melts, typically the next
place it goes, it infiltrates the soil.  So soil is not soli
It's not like a rock, there are pore spaces that can be filled with water and typically
there is a certain amount of water in the soil at all times.  If soil was completely dry, plants wouldn't
be able to grow.  [Narrator] If soil becomes saturated,
any additional rainfall will collect in puddles and streams.
Soil water that percolates deep enough will help to recharge an aquifer.
[Matt Rodell] An aquifer is any underground geologic formation
that stores water so it’s typically either rock with a lot of cracks
or it's sandy layer, sand has a lot of pore space in it.
and can store a lot of water.  [Narrator] The water molecule might remain in an aquifer
for more than a million years.  More likely, it would help to replenish a
which would feed into lakes and rivers. Eventually, the water molecule
will return to where it started: the ocean.
[music]
People also have a role in the water cycle. By pumping water out of the ground for irrigation,
cutting down forests for development and building roads and other concrete surfaces
that lead to runoff, people can have a serious impact on the path a water molecule takes.
[Matt Rodell] The most obvious way that people affect the water cycle are the ways that
we control the water after it’s fallen on the land surface as
rain or melts as snow…But we have put in dams and rivers to
hold this water.  We’ve also pumped water out and use that.
So it's these water resources, as we call them, are really us taking a natural part of the
water cycle and using it to our beneift.  [Narrator] The water cycle also
affects and is affected by climate variations.
[Matt Rodell] The water cycle is one of the ways we will feel any changes in
climate.  So climate changes will feed back to water cycle changes, how much precipitation an
area  the frequency of droughts and floods and this sort of thing.
[Narrator] The water cycle is the adventurous journey that water takes through the oceans,
atmosphere, and land, driven by the sun.
Improving our understanding of the water cycle and how it is changing will be critical for
future decisions related to water management, agriculture, natural
resources, and climate change.
