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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 Informa tion 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 permanent 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
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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 manageme nt 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
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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. References Ballatore G.P., Fierotti G. (1967), Carta dei
suoli della Sicilia. Ist. Agron. Gen., Università di Palermo. Basso
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Taberner M. (2000). Evaluating environmental sensitivity at the
basin scale through the use of geographic information systems and
remotely sensed data: an example covering the Agri basin (Southern
Italy). Catena 40, p. 19-35. Carnemolla S., Drago A., Perciabosco
M., Spinnato F. (2001). Metodologia per la redazione di una carta
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