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The Hydrologic Cycle
Water Moves
From Land and Ice to Ocean to Atmosphere in the Hydrologic Cycle
By Matt Rosenberg
The hydrologic cycle is the
process, powered by the sun's energy, which moves water between the oceans, the
sky and the land.
We can start our examination
of the hydrologic cycle with the oceans, which hold over 97% of the planet's
water.
The sun causes evaporation of
water on the surface of the ocean.
The water vapor rises and
condenses into tiny droplets which cling to dust particles. These droplets form
clouds.
Water
vapor usually remains in the atmosphere for a short time, from a few hours to a
few days until it turns into precipitation and falls to the earth as rain,
snow, sleet, or hail.
Some precipitation falls onto
the land and is absorbed (infiltration) or becomes surface runoff which
gradually flows into gullies, streams, lakes, or rivers.
Water in streams and rivers
flows to the ocean, seeps into the ground, or evaporates back into the
atmosphere.
Water in the soil can be
absorbed by plants and is then transferred to the atmosphere by a process known
as transpiration.
Water from the soil is
evaporated into the atmosphere. These processes are collectively known as
evapotranspiration.
Some water in the soil seeps
downward into a zone of porous rock which contains groundwater.
A permeable underground rock
layer which is capable of storing, transmitting, and supplying significant
amounts of water is known as an aquifer.
More precipitation than
evaporation or evapotranspiration occurs over the land but most of the earth's
evaporation (86%) and precipitation (78%) take place over the oceans.
The amount of precipitation
and evaporation is balanced throughout the world.
While specific areas of the
earth have more precipitation and less evaporation than others, and the reverse
is also true, on a global scale over a few year period, everything balances
out.
The locations of the water on
the earth is fascinating.
You can see from the list
below that very little water is among us in lakes, the soil and especially
rivers.
World Water Supply by Location
Oceans - 97.08%
Ice Sheets and Glaciers - 1.99%
Ground Water - 0.62%
Atmosphere - 0.29%
Lakes (Fresh) - 0.01%
Inland Seas and Salt Water Lakes - 0.005%
Soil Moisture - 0.004%
Rivers - 0.001%
Ice Sheets and Glaciers - 1.99%
Ground Water - 0.62%
Atmosphere - 0.29%
Lakes (Fresh) - 0.01%
Inland Seas and Salt Water Lakes - 0.005%
Soil Moisture - 0.004%
Rivers - 0.001%
Only during the ice ages are
there noticeable differences in the location of water storage on the earth.
During these cold cycles,
there is less water stored in the oceans and more in ice sheets and glaciers.
It can take an individual
molecule of water from a few days to thousands of years to complete the
hydrologic cycle from ocean to atmosphere to land to ocean again as it can be
trapped in ice for a long time.
For scientists, five main
processes are included in the hydrologic cycle:
1) condensation,
2) precipitation,
3) infiltration,
4) runoff, and
5) evapotranspiration.
The continuous circulation of
water in the ocean, in the atmosphere, and on the land is fundamental to the
availability of water on the planet.
Matt
Rosenberg, former Geography writer for ThoughtCo, is
an award-winning professional geographer who has covered the field of geography
on this website for more than fifteen years.
Experience
Matt has
published two books about geography, The Handy
Geography Answer Bookand The
Geography Bee Complete Preparation Handbook. Matt
has been featured on PBS and NPR and has conducted many interviews about
geographical topics for television, radio, and newspapers. In October 2006,
Matt was awarded the Excellence in Media Award from the National Council for
Geographic Education for his contributions over the years to the discipline of
geography.
Matt
Rosenberg is a former adjunct university faculty member in geography, city
planning and GIS intern for local government, newspaper columnist, and a disaster
manager for the American Red Cross. Matt served on more than two dozen major
disaster relief operations around the United States. He has traveled widely
across North America and has visited or studied in Europe, Asia, Africa, and
the Middle East.
Education
Matt
Rosenberg holds a master's degree in geography from California State University, Northridge and a bachelor's degree in geography from the University of
California, Davis. Matt's master's thesis was
titled Catastrophic Hazards of
Ventura County, California.
Matt is a
proud member of the Association of
American Geographers and the National Council for Geographic
Education.
Matt Rosenberg
I've
loved geography ever since I took a required class on urban and economic
geography my freshman year at college. It's a fascinating discipline that
incorporates diverse academic subjects to discover more about the earth and
where humans live. It's my goal to provide you with the Internet's number one
geographical community.
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