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Identification of areas sensitive to desertification in
Sicily Region
L. Giordano*, F.Giordano*, S. Grauso*, M. Iannetta*, M. Sciortino*, L. Rossi*,
G. Bonati**
* ENEA (Ente per le Nuove Tecnologie, l’Energia e l’Ambiente), Centro Ricerche Casaccia, Via
Anguillarese 301, 00060 Roma, Italy.
** INEA (Istituto Nazionale di Economia Agraria), via Barberini n. 36, 00187 Roma Italy.
Abstract
The aim of this study is the identification of areas sensitive to desertification in the region
of Sicily, one of the Italian regions most threatened by desertification due to climate and
land use change. The model used was developed in the framework of MEDALUS
(MEditerranean Desertification And Land USe) European project, which identifies the
desertification prone areas on the basis of the ESA (Environmentally Sensitive Areas)
index. The parameters used have been suitably integrated and processed by GIS obtaining
four indexes on Climate, Soil, Vegetation and Management Systems, which represent the
basis for the ESA assessment. The results obtained indicate that 6.9 % of Sicilian territory
is highly sensitive to desertification, 46.5 % has moderate sensitivity, 32.5% has low
sensitivity and only 7.2% is non-sensitive. In particular the most sensitive are the inland
districts of the provinces of Caltanissetta, Enna and Catania. However the availability of
data and the spatial scale used have not enabled us to take into account the soil and
groundwater salinization in coastal areas induced by irrigated agriculture.
1. Introduction
Desertification is a phenomenon affecting very large areas where the land has lost
productive capacity due both to human activities and natural causes. In order to
understand this, we must identify the physical and manmade processes and their
interrelations (Sciortino M. et al., 2000).
In order to implement the UNCCD (United Nations Convention to Combat
Desertification, 1996) and the Italian National Action Programme (N.A.P.), set forth in
Inter-Ministerial Committee for the Economic Planning (CIPE) Resolution n. 299 of
21.12.1999, the Regional and Basin authorities are called upon to define specific plans for
intervention, with the identification of the most sensitive areas to the risk of
desertification.
The CIPE Resolution also stated that the National Committee to Combat Drought and
Desertification, set up under Prime Minister’s Decree of 26.09.97 (Official Gazette n. 43
of 21.02.98), should promote and co-ordinate, with the contribution of technical and
scientific institutions and bodies, the adoption of the standards and methodologies most
suited to prevent and mitigate desertification.
The aim of this work is to identify the areas sensitive to desertification in the region of
Sicily by using and testing the MEDALUS (Mediterranean Desertification And Land USe
– European Commission, 1999) methodology.
The choice of Sicily as a pilot area is based on the geological and geo-morphological
layout, the climatic features and the socio-economic context, which make this one of the
Italian regions most vulnerable to desertification.
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The MEDALUS methodology (Basso F. et al., 2000) aims at assessing sensitivity to
desertification by applying the so-called ESA Index (Environmentally Sensitive Areas).
Environmental sensitivity can be defined, in this context, as the degree of reactivity of the
ecosystem, in particular of the soil, to strains produced by external disturbing agents
(Sequi & Vianello, 1998) both of anthropogenic and natural origin (biological,
geodynamic or climatic agents). The conceptual approach of the MEDALUS model is
shared by other models used to identify the areas sensitive to desertification, whether on
the national level as in Greece and Portugal or on the regional level as in Sardinia, Puglia,
Basilicata and Sicily.
2. The Medalus methodology
The areas sensitive to desertification are identified by the combination of 4 quality
indexes about:
- Soil
- Climate
- Vegetation
- Land management
The first three quality indexes provide a picture of the environmental conditions while the
last one expresses an assessment of the pressure resulting from anthropogenic activities.
The methodology is based on the classification of each quality index obtained as the
geometric mean of the available environmental and anthropogenic parameters. The
available parameters are quantified in relation to their influence on the desertification
processes assigning a score to each. We tried, as far as possible, to use the classifications
adopted by the MEDALUS methodology. However MEDALUS does not prescribe the
number and type of classes, leaving the necessary flexibility to adapt to the data
availability.
The scores assigned to the different parameters range between 1 (best value) and 2 (worst
value).
The quality indexes were estimated utilizing the following parameters and formulae:
SQI (Soil Quality Index) = (Parent material *Texture * Soil Depth * Slope)1/4
CQI (Climate Quality Index) = Aridity
VQI (Vegetation Quality Index) = (Fire risk * Erosion protection * Drought resistance *
Plant Cover)1/4
MQI (Management Quality Index) = (Intensity of land use * Protection policies)1/2
The geometrical average of the parameters, referring to each of the four indexes
mentioned above, has been classified according to regular intervals (i.e. same range)
shown in Table 1, representing quality classes on a downwards scale.
Table 1 - Quality classes
Class Range
High 1 – 1.33
Medium 1.34 – 1.66
Low 1.67 – 2
The final overall ESA index is obtained as a geometrical average of the quality indexes.
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ESA = (SQI * CQI * VQI * MQI)1\4
The integration, management and processing of data were performed by means of
ArcView Geographical Information System and its Spatial Analyst extension.
3. Sensitivity of the MEDALUS model
The hypotheses used by the MEDALUS model for the identification of the sensitive areas
derive from research and field experiments activities. The model applies a geometrical
average of the four quality indexes, in order to provide a sensitivity diagnosis.
The model implicitly assumes that each of the four indexes taken individually has only a
limited capacity to influence the final value of the ESA index and that only when several
parameters have a high score, an area can be assigned to a high sensitivity class. This
hypothesis is in agreement with what is currently known and implies that no
environmental condition on its own can exclude or determine the possibility of the risk of
desertification. With regard to climate, for example, even if there is an arid climate, which
in the model is classified in the highest risk category, this is not a condition of sensitivity
to desertification if the conditions of the land, vegetation and management of farming
activities are good. On the other hand, a humid climate, classified in the model in the
excellent category, cannot exclude a priori a risk of land degradation due to manmade
activities. Current knowledge about desertification confirm this assumption. The
MEDALUS model allows for a change in the number of parameters to be used to assess
the quality indexes. We used four parameters for the soil, four for vegetation, one for the
climate and two for management quality on the basis of the available data for the entire
Sicily region. As a consequence the model has different sensitivity to the parameters used
to assess the four quality indexes. Sensitivity to the change in soil and vegetation
parameters will, in fact, be proportional to the fourth root of the value of the parameter
while sensitivity to change in management parameters will be proportional to the square
root; the climate is directly proportional. The sensitivity of the model to changes in the
numerical value of the parameters is thus lower as the number of parameters used to
assess the quality index increases. This differing sensitivity to parameters does not reflect
real physical phenomena and this empirical approach can only be considered therefore a
first approximation.
The model does not introduce variables taking into account trends due to the climatic
variations and land use changes, although the dynamic component of the phenomenon of
desertification is essential. Also the occurrence of meteorological and hydrological
drought, that severely affected Sicily in recent years, are not explicitly addressed in the
model.
To overcome the limitations of the MEDALUS model herein identified it would be
necessary further research and the application of the model to different environmental and
socio economic context to validate and verify the applicability and usefulness of its
results.
4. Soil quality
The soils of Sicily are characterised by a large variety, going from less to more developed
pedologic types (Fierotti et al., 1988). This is due to the different geolithological
formations (sedimentary to volcanic to metamorphic) and to the climatic conditions
varying from summer aridity with hot temperatures to winter rainy weather with mild
temperatures. In addition, natural soil characteristics are likely influenced by intense
cultivation made by populations which since millenniums inhabited the island.
The most widespread soil associations, covering on the whole about 21 % of land surface,
are represented by the eutric regosols – eutric/vertic cambisols with eutric fluvisols
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typically developed on the clayey hills largely occupying the inner Sicilian landscape,
mainly in the Agrigento and Caltanissetta provinces.
Secondly, the associations given by lithosols and eutric cambisols – orthic luvisols –
eutric regosols/lithosols, mainly developed on mountain morphology, covers about 17 %
of land surface. These are represented on main relieves such as the Madonie, Nebrodi,
Erei and Sicani ridges but also on some hilly locations like that comprised between
Sciacca and Ribera (Agrigento Province). The bedrock is mainly constituted by flysch
sequences (sandstone and clays) and limestone.
About 14 % is represented by soil associations developed on M.nt Etna flanks, comprising
rock outcrops, lithosols, eutric regosols, eutric cambisols of volcanic origin.
The associations eutric cambisols – calcic cambisols – lithosols and eutric cambisols –
vertic cambisols–chromic/pellic vertisols, developed on the flat or low-hills
morphologies with limestone and dolomitic substratum characterising the south-eastern
Sicily (provinces of Ragusa and Siracusa), cover altogether about 12 % of land surface.
The last largest association, covering on the whole about 10 % of land surface, is that
given by the soils of the main alluvial plains of the island, such as the Catania, Milazzo,
Gela and Licata plains, and of the major valley-floors.
The other soil associations which have been recognised in Sicily (lithosols, eutric and
calcaric regosols, eutric cambisols, luvisols etc.), covering the remaining almost 26 % of
land surface, are scattered on fragmented combinations of different lithologies and
morphologies.
In order to set up the Soil Quality Index (SQI) the following parameters were used,
correlated with the water retention capacity and resistance to erosion: parent material,
texture, soil depth and slope.
4.1 Parent material
Information on parent material was derived from the Lithological Map of the Sicily
Regional Countryside Plan in digital format, scale 1:250.000. Here, the various
formations constituting the geological bedrock are grouped in 9 lithological complexes:
clayey sandstone complex, clayey c., carbonate c., unconsolidated clastic c. of continental
origin (alluvial, lacustrine, foot-slope deposits), conglomeratic sandstone c., evaporite c.,
slaty and metamorphic c., sandy-calcarenitic c. and volcanic c. Among these, the clayey
complex is by far the lithology which characterises the most part of Sicilian landscape.
Clayey formations are widespread in the central part of the island covering the foot of
inner rocky relieves and constituting a hilly belt extending from the inland to the southern
coast. The carbonate and sandy-calcarenitic complexes are following for extension, being
mostly present in western and south-eastern corners of the island. The clayey sandstone
and the metamorphic complexes are more limited and outcropping at the north-eastern
edge (Peloritani-Madonie mountains). The volcanic complex is represented by the mount
Etna structure and secondly by some older outcrops southward of Catania plain. Evaporite
complex forms some rocky ridges in central Sicily, surrounded by the clays complex.
Continental unconsolidated deposits are widespread throughout the territory and are
mainly represented by alluvial valley-floors. The last complex, conglomeratic sandstones,
is the less extended, being limited to few outcrops along the northern belt of the island.
On the basis of the consideration that different geological substrata, in relation to their
petrology and mineralogy, favour the development of different types of soil with different
behaviour regarding phenomena of erosion and desertification, the following 3 classes
have been identified (see Table 2)
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Table 2 – parent material classes
Class Description Score
Unconsolidated clastic; Slaty –
metamorphic; Volcanic; Conglomeratic-
sandstone
good 1
Carbonate; Sandy – calcarenitic;
Evaporite; Clayey sandstone medium 1.5
Clayey poor 2
4.2 Soil depth
The soil depth is closely related to the possibility of establishing or maintaining various
types of vegetation which play a fundamental role in preventing erosion. The soil depth
parameter was derived from the pedological map of the Sicilian region (Fierotti et al.
1988), available in digital format, scale 1:250.000. A remark is necessary in this regard.
Due to the coarse spatial resolution , the subdivision into homogeneous areas, associated
with the different information shown in the map legend, were made in relation to soil
associations identified in the numerous pedological studies conducted in Sicily after the
publication of the previous soil map by G.P. Ballatore and G. Fierotti (1968). This means
that with regard to soil depth but also to texture, various differing features can coexist in
the same mapping unit. This fact is reflected in the classification of the parameter shown
in Table 3. The extreme classes are described in a more definite way including the
categories "very thick" and "thin" or "very thin". The intermediate categories, on the other
hand, are broader and therefore less well defined. For some zones (approximately 10%) in
particular the information contained in the pedological map is ambiguous since depth can
have values "from thin to very thick".
Table 3 - Classes of soil depth
Class Description Score
Very thick very good 1
From medium to thick
From thin to very thick
Medium
From medium to thin
good 1.33
From medium to very
thin
From thin to medium
From very thin to
medium
poor 1.66
From very thin to thin
Very thin very poor 2
4.3 Texture
The pedological map mentioned above was also used for soil texture. The difficulty we
encountered here was in trying to express a sound correspondence between the texture
classes adopted in the Medalus model and the texture categories represented in the quoted
map. First of all, it must be recalled that the categories Fine, Medium and Coarse, referred
to the FAO system, correspond respectively to clayey, loamy and sandy textures of the
USDA classification. Then, the soil texture characteristics are expressed as composite
classes where the order of appearance reflects a quantitative criterion in the sense that the
prevailing type comes first and then the others. The medium texture guarantees the best
conditions for water retention capacity and drainage. The coarse texture does not enable
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the soil to retain water sufficiently. On the other hand, the fine texture makes drainage
difficult and insufficient.
Table 4 – Texture classes
Class Description Score
Medium-Fine-Coarse
Medium-Coarse
Medium
Medium-Fine
good 1
Coarse-Fine
Fine-Medium medium 1.33
Fine poor 1.66
Coarse very poor 2
4.4 The slope
The slope indicator was derived from a Digital Elevation Model (DEM) grids of 250 m,
provided by the National Geological Service. The slope is a crucial factor in the processes
of soil erosion. In order to trigger an erosion process a certain critical angle is required; as
this increases, so does the extent of the erosion. Table 5 shows the slope classes adopted.
Table 5 – Slope classes
Class
(%) Description Score
< 6 very gentle 1
6 - 18 gentle 1.33
19 - 35 steep 1.66
> 35 very steep 2
4.5 Soil quality index
Soil quality is a highly important factor, especially in relation to the capacity to sustain the
growth and maintenance of vegetation. The parameters utilised in the present assessment,
Parent material, Depth, Texture, Slope, are available in existing soil maps and reports.
They are all significantly linked to this capacity and contribute altogether to create more
or less favourable conditions.
The soil quality was estimated using the Soil Quality Index (SQI) as the geometrical
average of the described parameters:
SQI = (Parent material* Texture * Depth *Slope)1/4
The values obtained were classified according to regular intervals (i.e. same range) as
shown in Table 1, representing generic quality classes on a downwards scale.
Figure 1 shows that in Sicily there is a prevalence (approximately 72%) of medium
quality soils. The high quality class is mainly represented in the central and southern part
of the province of Catania, in the North-western part of the province of Ragusa and
throughout the province of Trapani. In addition, all the coastal plains (Gela, Licata,
Milazzo, Partinico-Alcamo and the south-eastern part of the province of Siracusa) also
show high quality. The poor quality soils have a more fragmented distribution and are
mainly located in the province of Palermo.
These results suggest that the soil quality index is mainly influenced by the slope
parameter, in fact the areas marked by high soil quality index correspond with the major
alluvial plains and valley-floors and with morphologic-structural plateaus; while, in the
same way, the areas marked by the worst quality index correspond with the steepest
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slopes of mountainous areas. This is not surprising if we consider that, under the same
texture conditions, a soil can achieve an optimal depth and, consequently, a high quality
score, on a flat to gentle sloping morphology.
Figure 1 - Soil quality
5. Climate quality
The aim of the Climate Quality Index (CQI) in the MEDALUS model is to assess the
water availability to vegetation and for this purpose the three parameters aridity, yearly
rainfall and slope aspect are used. For the present application to the Sicilian Region, it
was decided not to take into account the rainfall and slope aspect parameters. Rainfall and
aridity are strongly correlated and for our purposes the use of both parameter would only
produce a duplication of data. Slope aspect was neglected because in the present
application the spatial scale is much larger than in the original applications to the Agri
Basin, Lesvos Island and Mertola municipality (European Commission (1999)). The slope
aspect is an important parameter at local scales but at regional or larger scale does not
improve the assessment of sensitivity.
The climatic data of the Sicilian Region used for this work have been extracted from the
“Atlante Climatologico della Sicilia” (Regione Siciliana, 2000)
The assessment of climate in Sicily is based on the availability of a network of 55
thermopluviometric and 127 pluviometric stations with continuous and reliable records
for the period of reference 1965 – 1994.
The Thornthwaite-Mater method was used for the evaluation of the hydrological balance
of the soil. The method requires the calculation of the potential evapotranspiration (PET)
on a monthly basis. The aridity is calculated according to the following:
I = [(P - PET) / PET] * 100
where:
P = average annual precipitation (mm)
PET = average annual potential evapotranspiration (mm), deriving from the sum of the 12
values of average monthly PET.
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Positive I values indicate humid climates, and negative values indicate dry to sub-humid,
semi-arid and arid climates. The latter, being characterised by water deficit, i.e. by PET
values much higher than precipitation, lead to an especially fragile balance between
human activities and the environment, exposing the land to a greater risk of
desertification.
The Thornthwaite climatic classes were associated to Quality Class as shown in Table 6.
Table 6 – Thornthwaite overall humidity index, I
Climate I Score Class
Very humid, Humid,
Sub-humid - humid > 0 1 High
Dry-subhumid 0 ÷ -33 1,5 Medium
Semi-arid - 33 ÷ - 67 2 Low
In the territory of the Sicily Region the Thornthwaite index identifies climatic conditions
ranging from "semi-arid", in particular in the south-central area, to "sub-humid, humid
and very humid" mostly occurring in the North-Eastern (Nebrodi and Peloritani
Mountains) and in the Mount Etna area.
The semi-arid areas cover about 1.1 million hectares, i.e. 45% of the regional territory,
covering most of the provinces of Trapani, Agrigento, Caltanissetta, Ragusa, Syracuse,
Catania, Enna and a small part of the province of Palermo.
The areas ranging from dry to sub-humid cover about 998,000 hectares (39%) of the
regional territory and characterise part of the provinces of Trapani, Agrigento, Ragusa,
Syracuse, Enna, Messina and Palermo.
In the provinces of Palermo, Messina and Catania we find sub-humid to humid areas
covering about 198,000 hectares (7.8%), humid areas of about 195,700 hectares (7.7%)
and very humid areas (0.6%).
Figure 2 – Climate quality
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Figure 2 shows that most of the territory is characterised by poor (approximately 45%) or
medium quality (approximately 39%). Only 15% of the region has good climate quality,
mainly associated with the mountains and other morphological features of the provinces
of Messina, Catania and Palermo.
The territory of the province of Messina is, in fact, mainly mountainous, half being in the
area of the Nebrodi Mountains while the rest is in the Peloritani Mountains. The latter,
with precipitation ranging from 770 mm on the Tyrrhenian side to 880 mm on the Ionian
side, is the most rainy area in Sicily, together with some areas on the eastern side of
Mount Etna. The province of Palermo is also characterised by hilly and mountainous
areas (the Madonie and Sicani). In particular, areas around Palermo show rates of about
850 mm (the most rainy part of the province) and the Madonie mountains, where annual
rates are around 710 mm.
The areas with poor climate quality are mainly in the coastal areas of Trapani, Agrigento,
Ragusa, Syracuse, the entire province of Caltanissetta, the inland hilly areas of Catania
and partly in the province of Enna. In particular, the coastal plain area (Gela) and the
southernmost hills of Caltanissetta are the most arid zone of Sicily, with about 415 mm of
annual average precipitation (compared to the regional average of 630 mm). The province
itself, like the province of Enna, shows an annual average rainfall of 480 mm, about 25%
less than the regional average.
6. Vegetation quality
The Vegetation Quality Index (VQI) was assessed using the following parameters: fire
risk, erosion protection, resistance to drought, plant cover.
The information on vegetation was derived from the updated land cover map (scale
1:100.000), provided by the Istituto Nazionale di Economia Agraria (INEA, 2001).
The territory of Sicily is mainly characterised by anthropogenic vegetation and natural
vegetation is confined to the less accessible zones. Agricultural areas cover 57% of the
island , whose 35% are arable lands and 22% permanent crops. Woodlands and semi-
natural areas which includes forests, shrublands, and open areas with sparse or absent
vegetation cover 32%. Within this broad class the map of vegetation (Regione Siciliana,
1996) estimated that forested surfaces are about 8%, natural grasslands 13% and macchia
4% of the regional territory.
The information provided by the INEA specifically accounts for the predominance of the
anthropogenic vegetation in Sicily. The legend uses the standard adopted within the
CORINE European Union project, except for the class “agricultural areas” fatherly
subdivided into four sub-levels. The “woodlands and semi-natural areas” class gives a
broad description of the non agricultural vegetation. The assessment of the agricultural
vegetation land cover is therefore more detailed than the “woodlands and semi-natural
areas”.
6.1 Fire risk
Fires are one of the main causes of soil degradation and desertification in Mediterranean
environments. Their increased frequency in recent decades is causing serious
consequences on erosion rate, biodiversity, and physical-chemical properties of the soil
such as availability of nutrients and permeability.
Mediterranean vegetation is highly inflammable due to the presence of species with a high
content of resins and essential oils, but also has a good recovery capacity, occurring
gradually over a few years.
In relation to fire risk, the land use classes on the land cover map were grouped into 3
classes, with scores assigned to each as shown in Table 7.
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Table 7 - Fire risk Class Description Score
Annual crops associated with permanent crops, irrigated
and non irrigated vineyards, irrigated and non irrigated fruit
trees, irrigated and non olive groves, greenhouses, open
field herbaceous with spring-summer cycle, horticulture
with summer/autumn/spring cycle, horticulture with
spring/summer cycle.
Low
1
Complex cultivation patterns, land principally occupied by
agriculture with significant areas of natural vegetation,
permanent grassland, non irrigated arable land
Medium
1.5
Woodlands and semi-natural areas
High
2
6.2 Erosion protection
Vegetation plays a fundamental role in protection against soil erosion, thanks to its
capacity to reduce the kinetic energy due to the impact of the rain drops on the soil, and
thus surface runoff. Furthermore, the plants root system increases the stability of the soil.
In relation to the capacity of protection against erosion, 4 classes were defined on the land
cover map with scores assigned as shown in Table 8.
Table 8 - Erosion protection Class Description Score
Woodlands and semi-natural areas Very high 1
Permanent grassland High 1,33
Annual crops associated with permanent crops, irrigated
and non irrigated vineyards, irrigated and non irrigated
fruit trees, irrigated and non olive groves, complex
cultivation patterns, land principally occupied by
agriculture with significant areas of natural vegetation
Medium
1,66
open field herbaceous with spring-summer cycle,
horticultures with spring-summer-autumn cycle,
greenhouses, non irrigated arable land
Low
2
6.3 Resistance to drought
Mediterranean vegetation is well adapted to irregular water supply and to long periods of
drought. The main strategy adopted for this purpose is the reduction of the leaf surface
which, while allowing for resistance to water shortage, also involves a reduction of the
vegetation and thus greater exposure to erosion processes.
On the basis of the resistance to drought, 5 classes were identified, shown in Table 9 with
the corresponding scores.
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Table 9 - Resistance to drought Class Description Score
Woodlands and semi-natural areas Very high 1
Irrigated and not irrigated olive groves High 1,25
Annual crops associated with permanen
t crops, irrigated and
non irrigated vineyards, irrigated and non irrigated fruit trees,
complex cultivation patterns, land principally occupied by
agriculture with significant areas of natural vegetation
Medium
1,5
Permanent grass land
Low 1,75
Open field herbaceous with spring-summer cycle,
horticultures with spring-summer-autumn cycle,
greenhouses, non irrigated arable land greenhouses, non
irrigated arable land
Very low
2
6.4 Plant cover
The continuity and wealth of plant species are essential elements for the capacity of
protection of the soil. Numerous studies have shown that generally, good vegetation
reduces and controls runoff and loss of sediment and consequently protects from erosion
phenomena.
When especially strong precipitation hits areas with little vegetation, the water is only
slightly blocked by the plants and it often causes violent runoff that may remove the
topsoil, rich in organic material and thus indispensable for the growth of vegetation. All
this involves a reduction of the reproductive capacity of the land.
The presence of vegetation is likewise important since it continuously provides fragments
of biological material that are absorbed and converted into organic substances, thus
endowing the soil with greater capacity to absorb water.
In relation to plant cover, the 4 classes shown in Table 10 were identified.
Table 10 – Plant cover Class Description Point
Woodlands, semi-natural areas and permanent
grasslands Very high 1
Annual crops associated with permanent crops, ,
horticultures with spring-summer-autumn cycle,
greenhouses
High
1,33
Open field herbaceous with spring-summer cycle,
horticultures with spring-
summer cycle, irrigated and
non irrigated vineyards, irrigated and non irrigated fruit
trees, irrigated and non olive groves, complex
cultivation patterns, land principally occupied by
agriculture with significant areas of natural vegetation
Medium
1,66
Non irrigated arable land Low 2
6.5 Vegetation quality index
The quality of vegetation was estimated by the Vegetation Quality Index (VQI) as the
geometrical average of the thematic levels composing it:
VQI = (Fire risk * Erosion protection * Resistance to drought * Vegetation)1/4
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The values obtained were assigned to quality classes as shown in Table 1.
Figure 3 - Quality of vegetation
The map of vegetation quality highlights that Sicily is subdivided into about equal areas
of high (30.3%), medium (31.7%) and low quality (30.7%). The best conditions are those
in the province of Messina. This zone has the largest wooded areas of the region, and
despite the high fire risk, they protect the land from desertification, mainly thanks to the
amount of vegetation, good resistance to drought and high protection from erosion.
The provinces most characterised by poor vegetation quality are Caltanissetta, Enna, and
partly Palermo and Agrigento, with mainly non irrigated arable land grown in inland hilly
areas with greater slopes and inappropriate agronomic techniques.
7. Management quality
The Management Quality Index takes into account the stress produced by the human
factor. The indicators used are the land use intensity and the land protection policy,
considering their significant impact on natural resources (soil, water, vegetation etc.) in
the concerned area.
7.1 Intensity of land use
In order to assess the intensity of land use, we have used the land cover map produced by
INEA. The various classes of the legend have been suitably grouped into just 3 classes, as
homogeneous as possible with regard to the intensity of land use and its consequences on
soil degradation and associated desertification processes (see Table 11).
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Table 11 - Intensity of land use
Class Description Point
Woodlands, semi-natural areas and natural grasslands Low 1
Irrigated and non irrigated vineyards, irrigated and non
irrigated fruit trees, irrigated and non irrigated olive
groves, annual crops associated with permanent crops,
complex cultivation patterns, land principally occupied by
agriculture with significant areas of natural vegetation,
non irrigated arable land
Medium
1,5
Open field herbaceous with spring-summer cycle,
horticultures with spring-summer cycle, horticultures with
spring-summer-autumn cycle, greenhouses
High
2
7.2 Protection policies
Regional and national laws provide rules for the land management that regulate the
exploitation of land and water resources. This rules are often in conflict with local interest
and are perceived as a constraint to local development. For this reason their
implementation is often insufficient to preserve the environment. The Protection policies
indicator should be improved including information on the effective implementation of
policies.
The identification of the protected zones was based on the map produced within the
Regional Countryside Plan (Regione Siciliana, 1996). Three classes were considered:
reserves, parks and archaeological areas were taken separately, considering their greater
protection rate compared to woodlands, semi-natural and coastal areas. Finally, there were
the areas not subject to restrictions (v. Table 12).
Table 12 – Protection policies
Class Description Point
Reserves, parks and archaeological areas High 1
Woodlands, semi-natural and coastal areas Medium 1.5
Areas not subject to restrictions Low 2
7.3 Management Quality Index
The Management Quality Index (MQI) has been calculated as the geometrical average of
the land use and protection policy indicators:
MQI = (Intensity of land use * Protection policies)1/2
The values obtained were assigned to quality as shown in Table 1.
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Figure 4 – Management quality
About half of the region (56%) falls into the worst class. The greatest rate of land use
intensity, with the connected problems of soil degradation is found in irrigated areas, i.e.
crops requiring artificial irrigation, permanent or periodical. In these areas there is a
strong competition for the use of water among the various economic sectors.
It should be recalled that in many irrigated areas in Sicily, especially in coastal areas,
groundwater used for irrigation has a high saline content because of salt intrusion due to
excessive and extended exploitation. In various areas this has led to serious problems of
increasing salinity and degradation of the soil, further aggravated by the presence of clay
soils and the increasing scarcity of atmospheric precipitation.
In inland hilly areas, there is a serious risk of erosion, linked in particular to autumn-
spring cereal crops, which ensure a partial soil cover only for a period of the year. The
land is practically bare and exposed to erosion by rainfall in the period of maximum
precipitation.
8. The ESA index
The final ESA index on desertification was calculated as the geometrical average of the 4
quality indexes composing it:
ESA = (SQI * CQI * VQI * MQI)1/4
The values thus obtained were assigned to 4 classes of sensitivity as shown in Table 13.
Table 13 - Classes of sensitivity to desertification
Class Range
High 1.75 ESA 2
Medium 1.50 ESA < 1.75
Low 1.25 ESA < 1.50
Not affected 1 ESA < 1.25
15
As shown in Figure 5, the unaffected areas ( 7.2%) are mostly in the province of Messina
and, to a lesser extent, in the provinces of Palermo and Catania. The reasons for this result
are basically due to the climatic, vegetation and management factors which, in these areas,
have good quality characteristics, i.e. humid and very humid climates in extensive
wooded areas mostly protected in parks and reserves.
Most of Sicily nevertheless has medium (46.5%) or low (32.5%) sensitivity. It should be
recalled that in areas with medium sensitivity, the equilibrium between the various natural
factors and/or human activities might be especially delicate. Careful land management is
thus required to avoid triggering phenomena of desertification.
Finally, the areas with high sensitivity (6.9%) are concentrated in the inland districts of
the provinces of Caltanissetta, Enna and Catania and on the coastal strip in the province of
Agrigento. This result reflects the particular geo-morphological characteristics of the
inland areas of the region of Sicily (rather unstable clay hills), the intense human activity
with the consequent excessive exploitation of natural resources and the low amount of
vegetation. The excluded areas ( 6.9% ) include inland water surfaces, urban areas and the
slopes of the Etna volcano with bare rock (lava flows).
Figure 5 - The map of the areas sensitive to desertification
9. Conclusions
The results obtained by applying the Medalus methodology highlight the extension and
the intensity of the threat of desertification in the Sicily region. Field surveys and other
local assessments made by Sicilian academic institutions and regional authorities
(Carnemolla et Al., 2001) have confirmed the results presented in this paper.
It should nevertheless be pointed out that the Medalus methodology requires an expert
judgment for assigning the scores to the various classes. In most cases, in fact, the data
available are not in a form enabling immediate use. We should therefore assess the
available information to classify it in a suitable way. The choice of the intervals to
associate with the ESA classes likewise introduces a major subjective element that
16
conditions the final result of the assessments. The model, based on a simple calculation of
the geometrical average of the input data, cannot work without the contribution of experts
who have an in-depth knowledge of the land and the phenomena to be assessed. The
methodology can also be applied when some information is missing or with the addition
of new information. This characteristic makes it exportable and applicable to other
geographical areas. This allows comparative studies to be conducted on different areas,
though suitable changes related to specific local features and the characteristics of the data
available are sometimes required.
The processing of information layers using a Geographical Information System (GIS),
allows for the handling of considerable amounts of data rapidly and effectively, and for an
integration with new information that may derive from the processing of satellite images
and from further surveys or research.
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