Maria José Roxo – Pedro Cortesão Casimiro – Tiago Miguel Sousa
What is
Desertification?
DesertLinks Project
Framework 5 – European Union
Geografia e Planeamento Regional
Faculdade de Ciências Sociais e Humanas
Universidade Nova de Lisboa
What is desertification ?
“…degradation of the soil, landscape and
bio-productive terrestrial system, in arid,
semi-arid and sub-humid areas, resulting
from several factors, including climatic
change and human activities…”.
United Nations definition (1994)
The Desertification phenomenon has been
wrongly confused with Depopulation, which
affects a large portion of the inner part of the
country. However, these two phenomena can in
fact be related. The loss of soil fertility ends up
leading to a decline in agriculture, to land
abandonment and ultimately to emigration.
Desertification
Therefore it is essential to distinguish between the two phenomena, to allow for
correct and appropriate measures that combat Desertification and its advance.
Desertification is a progressive loss of soil fertility, through the destruction of
the structure and composition of the soil, which doesn’t permit good
agricultural productions, or the existence of a vegetation with varied
natural species.
Formation
Rock
Young Soils
Mature Soil
Erosion
The destruction of the soil has other
aggravants, as when the soil becomes
shallower, it allows only the infiltration of
small amounts of rainfall water. This wise,
the amount of underground water
decreases.
Recent studies have revealed that about 36 % of the country presents a serious
risk to Desertification, and that 28 % of this area is already severely affected by
this phenomenon.
Several areas of Inner Portugal (Alentejo, Algarve, Beira Interior, Trás-osMontes), present already vast areas high a high degree of soil and vegetation
degradation.
In the particular case of the Mértola municipality, 47% of its surface is already
affected by a high degree of degradation, which can be easily observed by the
enormous extensions with little vegetation and with many rock and stones on
the surface.
Desertification
Desertification Environmental
Sensitive Areas
Mértola Municipality 2001
Critical Areas
Fragile Areas
Non Affected Areas
Causes
There are several factors that contribute to
Desertification. Some are natural causes
(intense rainfall events, droughts), others
are directly related to human activities
(agriculture, industry, among others).
In reality, the conjunction of these factors has
had a very big negative impact on the natural
resources (soil, water and vegetation).
Agricultural activities, because they are
based on the use of soil, contribute
decisively to Desertification. Therefore, a
series of practices and actions, which are
bad and degrade the soils and the
environment, can be identified.
Desertification
Pastures
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Overgrazing – Excessive use of the same pastures;
Excessive density of animals per area;
Use of pastures not adapted to the soils and climate
conditions;
Compaction of the soil surface by cattle;
Appearance of a trail net, which favours the action of runoff
water.
Arable Lands
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Desertification
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Removal of the vegetation cover (cut,
stubble burn);;
Incorrect agricultural practices, like
ploughing too deeply, successively
and along the slopes, among others;
Loss of organic matter in the soil,
through soil wash by rainfall water;
Destruction of the soil structure, with
incorrect works (ploughing and other);
Compaction – use of heavy
machinery;
Stored nutrient removal (fallow) –
monocultures (e.g. wheat, vineyards,
among others), species inadequate to
the soil and climate conditions (e.g.
sunflower);
Pollution contamination by toxic
residues and chemical products
(fertilisers, herbicides, pesticides).
Irrigated Areas
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Incorrect agricultural
practices, like excessive use
of water and consequent
erosion;
Salinization – formation of
salt layers on the surface of
the soil, due to the use for
irrigation of groundwater with
high contents of salt;
Worrying decrease on the
quantity of available
underground water;
Loss of soil fertility by
continuous use – depletion.
Forest
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Deforestation;
Use of fast growing exotic species, like the eucalyptus;
Fires.
Desertification
Other activities
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Surface sealing – infrastructure and urbanization;
Excessive water consumption in tourist areas (e.g. Algarve).
All these activities lead and intensify the soil erosion processes by action of the
rainfall water. When rain drops hit the unprotected and disaggregated soil, they
fragment the soil aggregates into particles, which are afterwards easily
transported by surface run off water.
For that reason, it is common to
see the rivers with a clayish
colour, mainly during Autumn
(time of ploughing and seeding),
or in other times of the year,
when the occurrence of severe
rainfall events coincides with
agricultural labour on the soil
(like during Spring when fields
are ploughed).
Consequences
The consequences of Desertification are
very grave, despite being a phenomenon
that doesn’t occur like a sudden catastrophe,
but progresses steadily in time.
The main consequence is
land abandonment, following
the loss of soil fertility. There
is loss on the quality of life of
the populations, which makes
them emigrate.
Desertification
As a consequence of these
migratory movements, a
chaotic growth of town
receiving these migrants can
occur, which means
increasing unemployment and
marginal behaviours, as well
as pollution and other
environmental problems.
Several aspects result from
the loss of soil fertility :
• Breakdown of agricultural
production and productivity;
• Decrease of yield and
purchase power of the
populations;
• Oscillation of product prices,
at regional and national
markets;
• Social, economical and
political instability;
• Increase in wealth disparity
between regions;;
• Increase of environmental
problems due to the bad use
of natural resources;
• Poverty and unemployment.
In terms of natural resources, several issues are observable:
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Loss of biodiversity (less variety of plants and animals);
Soil loss by erosion, which implies less capacity for rainfall water to infiltrate
and feed groundwater tables and springs;
Decrease of sweet water availability, as rivers carry much sediment and dams
fill up with this load;
Degradation of “Montado”;
Progressive increase of the pressure upon the resources, in order to maintain
some income.
As it can be concluded, we stand before a very GRAVE phenomenon, to
which governments and populations haven’t paid the necessary attention.
Desertification
For this reason it is fundamental to realise that Desertification exists and
is in course, which makes it extremely urgent to take measures preventing
its further advance.
Despite there being a National Action Plan to Combat Desertification,
elaborated because Portugal signed the United Nations Convention to
Combat Desertification and Drought, it is in the hands of EVERYONE to
contribute for the conservation of vital resources for the human being, like
SOIL and WATER, as the FUTURE of all of us depends upon the actions
and attitudes of the Present.
Being informed is a decisive step to participate combating Desertification.
PANCD - Plano de Acção Nacional para
Combate à Desertificação – Aprovado
pela Resolução de Conselho de Ministros
nº 69/99 de 17 de Junho
Photos taken by the
authors, Mértola
Municipality – 2003/2004
Direcção Geral dos Recursos Florestais
sede do Ponto Focal da UNCCD
DesertLinks
http://www.kcl.ac.uk/kis/schools/hums/geog
/desertlinks/index.htm
Desertification
Faculdade de Ciências Sociais e Humanas
http://www.fcsh.unl.pt/
Framework 5
http://www.cordis.lu/fp5/home.html
Maria José Roxo
[email protected]
Pedro Cortesão Casimiro
[email protected]
Tiago Sousa
[email protected]