WATER AVAILABILITY
(cubic feet [cu m]
per capita/year)
Less than 60,000 cu ft
(1,700 cu m)
60,000-175,000 cu ft
(1,700-5,000 cu m)
More than 175,000 cu ft
(5,000 cu m)Less than 50% of the
populationSouth
AmericaEuropeAfricaOceaniaNorth
America AsiaPacific
OceanAtlantic
OceanArctic
OceanPacific
OceanIndian
OceanWHERE IT IS FOUND
A small percentage is
freshwater; most of it
is salt water.FRESHWATERUnderground
water
1%Ice
2%0.03%
water on
the surface
and in the
atmosphereLakes
0.029%Atmosphere
0.001%Rivers
0.00015%FRESHWATER3 %
SALT WATER97 %
T
he water in the oceans, rivers, clouds, and rain is in constant motion. Surface water evaporates,
water in the clouds precipitates, and this precipitation runs along and seeps into the Earth.
Nonetheless, the total amount of water on the planet does not change. The circulation and
conservation of water is driven by the hydrologic, or water, cycle. This cycle begins with evaporation of
water from the Earth's surface. The water vapor humidifies as the air rises. The water vapor in the air coolsand condenses onto solid particles as microdroplets. The microdroplets combine to form clouds. When the
droplets become large enough, they begin to fall back to Earth, and, depending on the temperature of the
atmosphere, they return to the ground as rain, snow, or hail.Living Water
GASEOUS STATE
The rays of the Sun
increase the motion
of atmospheric gases.
The combination of
heat and wind
transforms liquid water
into water vapor.FORMATION OF DROPLETS
The molecules of water
vapor decrease their
mobility and begin
to collect on
solid particles
suspended
in the air.LIQUID STATE
A rise in temperature increases the
kinetic energy of the molecules,
which breaks the hydrogen bonds.SOLID STATE
The molecules have very little
mobility because of the great
number of bonds they establish
with hydrogen atoms. They
form snow crystals.20 SURFACE FACTORS
EVAPORATION
Thanks to the effects of the
Sun, ocean water is warmed
and fills the air with water
vapor. Evaporation from
humid soil and vegetation
increases humidity. The result
is the formation of clouds.CONDENSATION
In order for water vapor to condense
and form clouds, the air must contain
condensation nuclei, which allow the
molecules of water to form
microdroplets. For condensation to
occur, the water must be cooled.PRECIPITATION
The wind carries the clouds toward the
continent. When the humid air cools, it
condenses and falls as rain, snow, or hail.72
OF WATER FALL EACH DAY IN
THE FORM OF PRECIPITATION.cubic
miles
cubic
milesTRANSPIRATION
Perspiration is a natural process
that regulates body temperature.
When the body temperature
rises, the sweat glands are
stimulated, causing perspiration.OCEANDISCHARGE AREARIVERCLOUDSWINDLAKEINFILTRATIONPERMEABLE
LAYERSIMPERMEABLE
LAYERSUnderground
aquifersRAINCONTRIBUTION OF LIVING SNOW
BEINGS, ESPECIALLY PLANTS, TO10%
THE WATER
IN THE
ATMOSPHERETHE HUMAN
BODY IS
65% WATER.All the
molecules
of water are
freed.Root cellsNucleusThe water vapor
escapes via
micropores in the
leaves' surface.3
The water ascends(^2) via the stem.
The root
absorbs water.
Some of the molecules
are set free.
The majority of
them remain
bonded.
1
6.
RETURN TO THE OCEAN
The waters return to the ocean, completing
the cycle, which can take days for surface
waters and years for underground waters.
5.
UNDERGROUND CIRCULATION
There are two kinds, both of
which are gravity driven. The
first occurs in a shallow zone, in
karstic rock such as limestone,
and consists of a downward flow.
The second occurs in aquifers,
where interstitial water fills up
the pores of a rock.
4.
RUNOFF
Water in liquid form runs off
the surface of the terrain via
rivers and valleys. In climates
that are not especially dry, this
phenomenon is the principal
geologic agent of erosion and
transport. Runoff is reduced
during times of drought.
300
years
THE AVERAGE LENGTH OF
TIME THAT A WATER
MOLECULE REMAINS IN THE
UNDERGROUND AQUIFERS
340
OF WATER CIRCULATE IN THE
TERRESTRIAL HYDROSPHERE.
WEATHER AND CLIMATE 21
AQUIFERS
Access to potable water