Water
resources. Global and local
Giuseppe Alonzo
ITAF Dept. – Faculty of Agronomy
–
90128
Water distribution on Earth
Earth appears from the space as a “blue” planet. The color
is due to the water covering about 71% of the whole Earth surface. Water also
is present in appreciable amounts under the land surface and as water vapor in the atmosphere. Because of the temperature and
pressure ranges available on the Earth, water is encountered in all the three
states of the matted and this has been considered of outmost importance for the
development of the life on this planet.
The Earth planet is an essentially closed system which
means that the matter leaving or entering the system is rather small. Water is
also therefore a finite resource which is cleaned and replenished in its
different forms through the hydrologic cycle.
The earth has an abundance of water, but
unfortunately, only a small percentage, about 0.3%, has characteristics usefull for its use by humans. The other 99.7% is in the
oceans, soils, icecaps or present in the atmosphere. Moeover,
much of the previously mentioned 0.3% is unattainable. Most of the water used
by humans comes from rivers, lakes or the underground provided these met the
required quality parameters. The rivers and lakes which are visible bodies of
water are referred to as surface water. The majority of fresh water is actually
found underground as soil moisture and in aquifers.
Following the U.S. Geological Survey, 1984, the
different forms in which the water is found in our planet are the following:
About 300 Km3 per day of water are needed
for human uses. Surface water is the easiest to reach and the most common
source of water, including potable water. Surface water provides as much as the
80 percent of the water used on a daily basis. Problems, however, exist due to
the increasing contamination of the water bodies thus further limiting the
amount of water available for human consumption. Water is found in many
different forms and in many different places. While the amounts of water that
exist seem to be plentiful, the availability of the water for human necessities
is limited.
Oceans, which are the largest source of surface water,
comprise approximately 97 percent of the earth’s surface water. However, since
the oceans have high salinity, the water is not useful as drinking water.
Efforts have been made to remove the salt from the water (desalination), but
this is a rather costly endeavor. The oceans also
play a vital role in the hydrologic cycle, in regulating the global climate,
and in providing habitats for thousands of marine species.
Glaciers and icecaps cover 10% of the earth’s surface.
Glaciers melting can have a tremendous effect on the sea level. If all of the
glaciers were to melt today, the rise of the sea would be about 78 meters.
Ground water is a very plentiful source of fresh water, it must be a protected resource. Once an aquifer is
contaminated with chemicals or petroleum, it is difficult, if not impossible,
to clean up. Many times, surface water also is in direct contact with
underground water and this can create a problem with contamination of the
ground water. There is also the problem of saltwater intrusion (present in
coastal regions) where over-pumping of the ground water draws the denser
saltwater up into the aquifer. So, protection of the ground water should be a
high priority as the population on Earth continues to rise and potable water
becomes a valuable resource.
The Water Cycle
The hydrologic cycle or more simply the “water cycle”
is a pictural representation of how water is recycled
through the environment. Water molecules remain constant, though they may
change between solid, liquid, and gas forms. Evaporation can occur from water
surfaces, land surfaces, and snow fields, into the air as water vapor. Moisture in the air can
condensate. Water vapor condenses on tiny particles
of dust, smoke, and salt crystals to become part of a cloud. After a while, the
water droplets combines with other droplets and fall
to Earth in liquid (rain) or solid (for example snow) forms. Once the drop has
fallen to Earth, it may go into an aquifer as ground water, or the drop may
stay above ground as surface water.
One problem facing the cycle of water on Earth is
water contamination. Chemicals that go into the water often are very difficult,
if even possible to remove. One potential source of contamination of water is
runoff, the overland flow of water. While precipitation causes the runoff to
occur, stripping vegetation from land can add to the runoff in a particular
area. The sediment and soil from these areas, not to mention any pesticides or
fertilizers that are present, are washed into the streams, oceans, and lakes.
What happens to the rain after it falls depends on
many factors, such as the intensity and duration of rainfall, the topography of
the land, soil conditions, amount of urbanization, and density of vegetation.
Water on Earth is a finite source. Protecting the
water means protecting all forms of the water found on Earth. Water at the surface, under the ground, in vapor
form, and as precipitation. Pollution from using fossil fuels can impact
all forms of water (from crude oil leaks to acid rain generated from coal
burning). Acid rain falls onto the land and flows into the surface water, back
into the ground, and back into the air. It can be an endless cycle. As
contamination infiltrates the water cycle, more water will be impacted. Most of
the water on Earth is saline. Fresh water is and will be in demand and become a
very valuable resource. Care must be taken to prevent overuse of potable water
sources. Care must also be taken to protect the earth’s waters from
contamination. Water is indeed a valuable resource.
Water resources in
Sicily
A variety of idro-orographical factors
influence the climatic characteristics of
The surface of
There are no major rivers in
If we consider that at least 50 liters of
water, including civic, industrial and agricultural activities, are required
per person and per day, following FAO recommendations,
it can be easy obtained that 0.25 Km3 of usable water would be
required by the whole sicilian people. During one
year, the amount of required water would be about 90 Km3.
Meteoric water in
Plants transpire water and thus requires replenishment at rates which are dependent on the plant microclimate
(leaf temperature, solar radiation, air humidity, wind speed), the plant age,
morphology, health, and the ease at which the water is available within the
root zone. In