1. Climate change and Urban Vulnerability in Africa
Assessing vulnerability of urban systems, population and goods in relation to natural and man-made disasters in Africa
“Training on the job” Course on Hazards, Risk and
(Bayesian) multi-risk assessement
Napoli, –
Module 3.5: Desertification, Methodologies
Iavazzo, Topa, Terracciano
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2. DESERTIFICATION: CAUSES
Desertification is a process of land degradation reducing its productivity and resulting from various factors, including climate variations and human activities (Warren, 1996)
So desertification is the final result of a complex system of interactions between natural and anthropic factors. Several indicators can be used to detect the progress of the desertification process.
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3. DESERTIFICATION: INDICATORS
frequency
In particular, in these charts we can see the most used indicators in Italian studies for monitoring desertification. Most common climate indicators are…
consecutive droughts
rainfall seasonality
annual rainfall
evapotranspiration
aspect
air temperature
water erosion
drought (year)
drought (month)
rainfall deficit
soil moisture
rainy days
rain coefficient
Climate indicators for desertification in Italy (Ceccarelli et al., 2006)
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4. DESERTIFICATION: INDICATORS
frequency
Most common pedological indicators are…
slope
soil depth
texture
parent material
rock fragments
drainage
erosion
AWC
wter regime
edaphic comp.
altitude
skeleton
soil temperature
lava
saline lithotype
distance from sea
irrigated areas
Pedological indicators for desertification in Italy (Ceccarelli et al., 2006)
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5. DESERTIFICATION: INDICATORS
frequency
Most common vegetation indicators are…
vegetation cover
drought resistance
fire
risk
erosion protection
Vegetation indicators for desertification in Italy (Ceccarelli et al., 2006)
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6. DESERTIFICATION: INDICATORS
frequency
Most common human pressure indicators are…
land use intensity
policy
pasture
demographic variation
natural areas
population density
roads and railways
urban sprawl
agricultural yields
SAU
biological SAU
water SAU
agro-environment
fire
aging index
occupation index
illiteracy index
retirement index
Human pressure indicators for desertification in Italy (Ceccarelli et al., 2006)
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7. DESERTIFICATION: DATA COLLECTION Vegetation map of Africa
Rainfall in Africa
Soil map of Africa
Land use of Africa
In order to assess and study the desertification in a study area it is essential to collect a great number of data which can help us to better recognize the characteristics of the area related to the desertification. Those are just some examples of maps that you can easily find on internet; of course the more detailed, the better.
Land cover of Africa
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8. Climatic and bioclimatic indices
METHODOLOGIES
Rain Use Efficiency
Climatic and bioclimatic indices
FAO/UNEP
There are several methodologies which have been used to study desertification in different areas. In particular we are going to focus our attention to these 3 methodologies:
MEDALUS
CRA-CMA
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9. Climatic and bioclimatic indices
Initially the climatic and bioclimatic conditions are analyzed on subcontinental scale by using indices as:
De Martonne’s aridity index
Lang’s factor
Emberger’s factor
AI Aridity index
P: mean annual rainfall
T: mean annual temperature
M: hotest month’s maximum temperature
m: coolest month’s minimum temperature
ETP: potential evapotranspiration (calculated by method of Thornthwaite)
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10. Climatic and bioclimatic indices
The De Martonne’s index identifies four types of climate: in particular when the index is less than 5 the zone is defined hyper-arid, when it is between 5 and 15 the zone is defined as arid, when it is between 15 and 20 it is defined as sub-humid and when the values are above 20 then the climate is defined as humid.
The climate classification according to Lang’s factor is the following:
P/T
Climate
≤40
Arid
Semi-arid
Subhumid
Humid
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11. Climatic and bioclimatic indices
The Emberg’s factor Q values are much lower than what the climate is arid, and in particular:
20<Q<30= arid
30<Q<50= semiarid
50<Q<90= sub-humid
Q>90= humid
By means of the Aridity Index can be delineated four arid zones: hyper-arid, arid, semi-arid and sub-humid. AI
Zone
AI < 0.03
hyper-arid
0.03<AI<0.2
arid
0.2<AI<0.5
semiarid
0.5<AI<0.75
sub-humid
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12. FAO/UNEP (1984) METHODOLOGY
The FAO/UNEP (1984) method is multidimensional methodology summarized by a matrix whose rows are quantitative and qualitative variables of vegetation and soil. The columns are classes of degree of desertification (slight, moderate, etc.). The elements of the matrix are, in the case of quantitative variables, the range of values of each variable corresponding to each degree of desertification status. In the case of qualitative variables, there are verbal descriptions instead of values.
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13. FAO/UNEP (1984) METHODOLOGY
PROBLEMS
LOGICAL PROBLEMS
PRACTICAL PROBLEMS
number of implicit assumptions underlying the matrix
subjective nature of data
Within the logical problems, the most relevant is likely the number of implicit assumptions underlying the matrix. For example, it assumes that 40% of perennial plant cover is equivalent to a 75% decline in plant production. In a similar way, a system with 10% of the area with exposed subsoil (slight desertification) and 25 cm of soil thickness (severe desertification) is made equivalent to a system with 15% of the area with exposed subsoil and 70 cm of soil thickness (moderate desertification). Another major avenue of criticism has been the subjective nature of their data as most variables were not measured but estimated by “informed opinion’’. Regarding the practical problems, the methodology was labour-intensive, which posed serious limitations to the frequency and/or the extent of assessments.
methodology labour-intensive
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14. ESAs (Environmentally Sensitive Areas) model
MEDALUS METHODOLOGY
MEDALUS (Mediterranean Desertification And Land Use) project
ESAs (Environmentally Sensitive Areas) model
Vegetation
Soil
In order to identify the desertification vulnerable areas (ESAs) the MEDALUS European project was developed and used in many Mediterranean countries (Greece, Portugal, Italy, Egypt). The various types of ESAs to desertification can be distinguished and mapped by using some key indicators for assessing land capability to degradation or land suitability for supporting specific types of land use. The key indicators for defining ESAs to desertification, which can be used at regional or national level, can be divided into 4 categories defining the qualities of soil, climate, vegetation and land management.
Climate
Land Management
ESAI (Index of Environmental Sensibility)

15. MEDALUS METHODOLOGY ESAI
Soil Texture
Rock Fragment
Slope Gradient
Soil Depth
Parent Material
Drainage
SQI
Soil Quality Index
CQI
Climate Quality Index
Mean Annual Rainfall
Aspect
Aridity Index
ESAI
Fire Risk
Erosion Protection
Drought Resistance
Plant Cover
Each of these parameters is grouped into various uniform classes with respect to its behaviour on desertification and weighting factors are assigned in each class. The 4 indices for vegetation, climate, soil and land management quality are calculated providing a measure of the inherent quality of the physical environment and the man induced stress of desertification.
VQI
Vegetation Quality Index
Land Use Type
Land Use Intensity
Policy
MQI
Management Quality Index
(Kosmas et al., 1999)

16. Soil quality indicators related to:
SQI
SOIL QUALITY INDEX
Soil quality indicators related to:
Soil quality indicators for mapping ESAs can be related to water availability and erosion resistance.
Water availability
Erosion resistance
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17. Surface rock fragment cover Slope grade
SQI
SOIL QUALITY INDEX
Soil texture
Surface rock fragment cover
Slope grade
Soil depth to limitating layers
Parent material
Drainage conditions
These qualities can be evaluated by using simple soil properties given in regular soil survey reports such as soil depth, soil texture, drainage, parent material, slope grade, stoniness, etc. The use of these properties for defining and mapping ESAs requires the definition of distinct classes with respect to degree of land protection from desertification.
(The definition of classes requires the study of relations such as: soil depth and plant cover under various climatic, lithological and topographical conditions, parent material and water availability, soil water holding capacity and soil texture. The following minimum data basis for soils at appropriate scale are required for definition of the ESAs to desertification at regional scale.)
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18. SQI SOIL QUALITY INDEX related to: erodibility
water retention capacity
crusting
aggregate stability
The amount of available water is related to both texture and structure. Soils high in silt (silt loam) tend to have the largest available water holding capacity. In the opposite, sands have the smallest available water holding capacity.
L: loamy; S: sandy; C: clayey; Si: silt
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19. SQI SOIL QUALITY INDEX effect on: run off soil erosion
soil moisture conservation
biomass production
Rock fragments present in soil surface are classified in 3 classes according to their capacity to conserve soil water and protect the soils from erosion. Beyond 20%, the limited space between fragments prevents development of scour holes and thus limits soil loss.
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20. SQI
SOIL QUALITY INDEX
Slope angle and generally topography are undoubtedly important determinants of soil erosion. Erosion becomes acute when slope angle exceeds a critical value and then increases logarithmically. Slope grade is classified in 4 classes according to the effect on soil erosion.
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21. SQI
SOIL QUALITY INDEX
Soil depth is defined as the depth of the soil profile from the soil surface to the top of the regolith or unweathered parent material. The critical depth can be defined as the soil depth in which plant cover achieves values above 40%. On soil less than that depth, recovery of the natural perennial vegetation is very low and the erosional processes may be very active resulting in further degradation of the land.
1.5
1.7 2
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22. SQI
SOIL QUALITY INDEX
Soil derived from different parent materials react differently to soil erosion, vegetation and desertification. The p.m. is defined using the geological map of the study area. The various types of p.m. are grouped into the following classes according to their petrology and mineralogical composition and their sensitivity to desertification.
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23. SQI
SOIL QUALITY INDEX
Soil drainage condition is mainly used for assessing desertification risk due to salinization.
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24. SQI
SOIL QUALITY INDEX
SQI = (texture * parent material * rock fragment * depth * slope * drainage) 1/6
Soil quality index is then calculated as the product of the previous attributes as the following algorithm.
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25. CQI Climate QUALITY INDEX
Amount of rainfall
Air temperature
Aridity
The following data on climate are required for the assessment of climate quality
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26. CQI Climate QUALITY INDEX
1.5 2
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27. CQI Climate QUALITY INDEX
Aridity zones of the world (WRI, 2002)
ti: mean air temperature for month i in °C;
Pi: total precipitation for month i in mm;
Ki: proportion of the month during which ti – Pi > 0.
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28. CQI Climate QUALITY INDEX
SLOPE ASPECT
NW – NE
SW - SE
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29. CQI = (rainfall * aridity * aspect) 1/3
Climate QUALITY INDEX
CQI = (rainfall * aridity * aspect) 1/3
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30. VEGETATION QUALITY INDEX
VQI
VEGETATION QUALITY INDEX
Fire risk and ability to recover
Erosion protection to the soils
Drought resistance
Plant cover
The dominant biotic land component in terms of desertification is the vegetative cover of the land. For the evaluation of the VQI are considered four factors related to the existing natural or agricultural vegetation.
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31. VEGETATION QUALITY INDEX
VQI
VEGETATION QUALITY INDEX
Fire cause a quick degradation of soil, due to an increase in the compactness which reduce the amount of water in filtration into the subsoil and increase the runoff. Furthermore, the reduction of vegetation cover implies a remarkable reduction of soil protection from the rain and wind.
In Mediterranean environment, fire is very frequent in the pine forest and in Mediterranean macchia (due to the high content of resins or essential oil), but it has a high ability to recover after fire.
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32. VEGETATION QUALITY INDEX
VQI
VEGETATION QUALITY INDEX
A reduced vegetation cover causes an increase of erosion and of surface run-off. A higher rate of soil loss occurs in crops that leave the soil exposed during the rain season, lower in Mediterranean macchia and forest that have a good cover all over the year.
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33. VEGETATION QUALITY INDEX
VQI
VEGETATION QUALITY INDEX
The various ecosystems present in the Mediterranean region (macchia, evergreen forest, conifers) present a great capacity of adaptation and resistance to drought, so the crops show the lower drought resistance.
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34. VEGETATION QUALITY INDEX
VQI
VEGETATION QUALITY INDEX
About plant cover we have three classes. Vegetation cover protect the soil from erosion and reduce runoff and soil loss.
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35. VEGETATION QUALITY INDEX
VQI
VEGETATION QUALITY INDEX
VQI = (fire risk * erosion protection * drought resistance * vegetation cover) 1/4
Geometric average of four indicators, 3 classes that correspond to 3 level of vegetation quality.
1 to 1.13
1.14 to 1.39
1.40 to 2
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36. MANAGEMENT QUALITY INDEX
MQI
MANAGEMENT QUALITY INDEX
Land use intensity:
Agricultural land (cropland, pasture)
Natural areas (forest, shrubland, bare land)
Mining areas
Recreation areas (parks, tourist areas, etc.)
Policy related to environmental protection
Land use can be classified according to several criteria leading to hierarchies of land use types. The number of criteria employed is dictated by the level of detail desired as well as by the availability of the proper data. The principal classification criterion is the main purpose for which land is used.
The last index is the MQI, since the definition of ESAs to desertification requires both key indicators related to the physical environment and to human induced stress. This index depends on the particular type of land use (agriculture, pasture, mining ecc) and its intensity, and on environmental policy.
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37. MANAGEMENT QUALITY INDEX
MQI
MANAGEMENT QUALITY INDEX
If the main use of land is agriculture, the intensity of land use for cropland is assessed by characterising the frequency of irrigation, degree of mechanisation, the use of agrochemicals and fertilisers, the crop varieties, etc. 3 levels of land use are distinguished as following:
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38. MANAGEMENT QUALITY INDEX
MQI
MANAGEMENT QUALITY INDEX
SSR: sustainable stocking rate; ASR: actual stocking rate
R: required annual biomass intake per animal (sheep or goat kg animal-1 year-1, FAO 1991);
X: fraction including grazing efficiency and correction for biomass not produced during the latest growing season (grazed: 0.5, non-grazed 0.25 year-1);
P: averaged palatable biomass after dry season (kg ha-1);
F: averaged fraction of the soil surface covered with annuals
The quality of management of pasture land can be assessed by estimating the sustainable stocking rate (SSR) and actual stocking rate (ASR), and than the intensity of land use is assessed by using the ratio of ASR to SSR and classified in 3 classes as in the table. This data are not easy to calculate and they are usually available from official source, for example for Burkina Faso from in Ministère des Ressources Animales.
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39. MANAGEMENT QUALITY INDEX
MQI
MANAGEMENT QUALITY INDEX
Forest natural and managed. The approach used involves assessment of the sustainable yield of a forest and its comparison to the actual yield by forming the ratio actual/sustainable.
A: actual yield; S: sustainable yield
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40. MANAGEMENT QUALITY INDEX
MQI
MANAGEMENT QUALITY INDEX
Mining activities have a highly degrading effect both during lifetime and after the end of the mining. The intensity of land use can be assessed by the erosion control (protection) measurements applied.
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41. MANAGEMENT QUALITY INDEX
MQI
MANAGEMENT QUALITY INDEX
A: actual number of visitors per year; P: permitted number of visitors per year
Assessment procedure would involve:
assessment of max number of visitors permitted per year;
assessment of the actual number of visitors per year;
calculation of the ratio of actual to permitted number of visitors per year.
Recreation activities are distinct in passive (walking, nature seeing, climbing) with low level of stress, and active recreation includes skiing, rallies with high level of stress. To assess the level of stress of this activities, is evaluated the ratio of Actual and Permitted number of visitors per year.
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42. MANAGEMENT QUALITY INDEX
MQI
MANAGEMENT QUALITY INDEX
Particular attention is given to the policies related to the land protection. Of course their effectiveness depends on the degree to which they are enforced, in particular to the extension of the protected area. The degree of enforcement is complete if the area under protection is higher than 75%...
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43. MQI MANAGEMENT QUALITY INDEX
MQI = (land use intensity * policy enforcement) 1/2
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44. PHYSICAL ENVIRONMENT QUALITIES LAND MANAGEMENT QUALITIES
MEDALUS METHODOLOGY
PHYSICAL ENVIRONMENT QUALITIES
LAND MANAGEMENT QUALITIES
SQI
CQI
MQI
VQI
The final step comprises the matching of the physical environment qualities and the management quality for the definition of the various types of ESAs to desertification. The 4 derived indices are multiplied for the assessment of the ESAs index (ESAI) as following:
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45. MEDALUS METHODOLOGY
In this table there are the types of ESAs. Two types of the ESAs (critical and fragile) including 3 subclasses in each type appear in this table.
Two type of ESAs is defined on a three-point scale, raging from 3 (high sensitivity) to 1 (lower sensitivity)
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46. MEDALUS METHODOLOGY
Three general types of ESAs to desertification can be distinguished based on the stage of land degradation:
Type A (critical ESAs): areas already highly degraded through past misuse, presenting a threat to the environment of the surrounding areas
Type B (fragile ESAs) : areas in which any change in the delicate balance of natural and human activity is likely to bring about desertification
Type C (potential ESAs) : areas threatened by desertification under significant climate change; if a particular land use is implemented with wrong criteria the impact will produce severe problems.
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47. Vegetation quality map Management quality map
MEDALUS METHODOLOGY
Soil quality map
Climate quality map
Vegetation quality map
Management quality map
All the data defining the four sub-index are introduced in a regional geographical information system (GIS) to obtain four maps of sensitivity areas to desertification based on the different indicators. This data are than combined to obtain the final map of ESAs. To a different color correspond different level of sensibility to desertification.
Map of ESAs
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The island of Levsos, Greece (Kosmas et al., 1999)