Vulnerability to Desertification in Lebanon Based on Geo-information and Socioec

Abstract: Desertification caused by land degradation and overexploitation of natural resources is threatening large parts of eastern and southern Mediterranean. The actual state of desertification sensitivity in Lebanon was spatially assessed using site specific environmental bio-physical indicators, demographic pressure and socioeconomic conditions. Bio-physical assessment included the aridity index derived from integrated assessment of the historical data for 48 climatic stations spread throughout the country, the new detailed soil map at 1:50,000 scale, and the updated land cover/use map at 1:20,000 derived from IKONOS 2005. The methodology also included livelihood conditions and poverty at local administrative “Caza” level. Results showed the integrated impact of local climate, soil and vegetation quality and socioeconomic conditions on sensitivity to desertification. A total of 78% of the territories have low and very low climate quality index preconditioning the sensitivity to desertification. Fourteen Cazas out of 26 in total, representing more than 66% of the country, have low socioeconomic satisfaction index. Furthermore, negative trends are alleviated by good quality relict soils and vegetation cover. The actual extent of desertification covers 40.48% of the national territory, much of which occurs under semi-arid climate, moderate or low soil and vegetation quality and poor living conditions. The outcome of this research adjusted the previous coarse estimates of desertification prone areas at the national level. Results allow for realistic, policy oriented local assessment for responsive land use planning and proactive sustainable, national and local land management in the context of the national action plan to combat desertification.

Key words: Integrated assessment, land degradation, east Mediterranean, sensitivity, sustainable land management.

1. Introduction??

Climate conditions, demographic pressure, poverty and mismanagement of land resources in the drylands multiply the severity of soil degradation and extent of areas prone to desertification resulting in land abandonment [1]. Lebanon is also threatened by desertification and overexploitation of natural resources. The sensitivity to degradation arises from the abrupt changes in topography with a striking diversity of climate and soils [2], vegetation cover [3] and accelerated soil erosion [4, 5]. Pressure is exacerbated by intensive agriculture causing soil salinity [6], land use change and reduction of green cover [7], rapid population and urban growth [8], overgrazing of marginal lands [9] and chaotic quarries expansion [10] beside the mismanagement of water resources leading to seawater intrusion and contamination of aquifers [11, 12]. A first assessment of desertification prone areas was completed in 2003 at 1:200,000 scale [13]. Given the small size of Lebanon, a more detailed scale was needed to account for local variability.

Areas with ratio exceeding 0.65 were considered humid and given a score of 1 with little negative effect of climate on sensitivity to desertification. Climate effect increased proportionally with the reduction of the AI ratio with maximal impact at < 0.05 range. 2.2 Soil Quality Index

The SQI (soil quality index) was the product of five parameters: PM (parental material), S (slope), SD (soil depth), T (texture) and OM (organic matter) content(Eq. (1)). For this purpose, the soil map at 1:50,000 scale [19] was used to assign scores to different soil types resulting in more mapping units reflecting local soil diversity. Consequently, soil depth, texture, and slope classes were modified and additionally segmented to match the complex orography of the country. Given the important role of OM in soil water retention and the soil/vegetation resilience to drought, the methodology was enriched by the inclusion of soil organic matter content. The SQI was assessed according to the following formula:

SQI = (PM × S × T × D × OM)1/5 (1)

The PMs were subdivided into coherent, moderately coherent and soft to friable. Given the large presence of eroded soils on slopping and steep lands and the importance of soil depth for water retention and root penetration, the SD (soil depth) layer was subdivided into five classes (Table 2). These were given the score of 1 (SD > 150 cm), 1.25 (100-149 cm), 1.50 (50-99 cm), 1.75 (10-49 cm) and 2 (< 10 cm), respectively.

2.3 VQI (Vegetation Quality Index)

Classes of the new land cover/land use map of

of the listed four quality indexes as follows:

SDI = (SQI × CQI × VQI × SEQI)1/4 (4)

The SDI was grouped into five classes showing the distribution of sensitivity to desertification (Table 3).

Different index layers—created using ARCGIS 9.3—were combined using the spatial analysis identity method. Identity creates a new coverage by overlaying two sets of features. The output coverage contains all the input features and only those portions of identity coverage features that overlap the input coverage are shown. The final sensitivity to desertification map was created using the quantities method [27] with the geometrical interval classification scheme which creates class breaks based on class intervals that have a geometrical series. The geometric coefficient in this classifier can change to optimize the class ranges. This ensures that each class range has approximately the same number of values and the change between intervals is fairly consistent. The integrated SDI adopted for the classification of desertification risk levels [27] varied from the best condition with a score of 1 to the worst with a value equal to 2. The minimum and maximum intervals in the final map were 1.256 and 1.880. The urban and rock classes were masked to reduce the error rate.

with little net return, this human factor can exacerbate the situation, if the olive oil production and oil marketability are not improved.

The middle western part of the country shows an overriding low and very low sensitivity to desertification. The climate of this area is sub-humid and humid with a mixed soil quality dominated by high and moderate quality vegetation and population having high and very high socioeconomic conditions. The two southern governorates, south and Nabatiye, are characterized by a mixture of sensitivity to desertification ranging from moderate to very high due to the prevailing semi-arid conditions and the mixed quality of the soil and vegetation covers.

The northern part of the eastern mountain chain or Anti Lebanon shows very high sensitivity to desertification potentially originating from the prevailing arid climate and the low quality soil and vegetation cover. Low living standards in the rural marginalized cazas must receive due attention as the average income in the agricultural sector is 200$·month-1 versus an average income of 335$·month-1 for the commercial sector and 535$·month-1 for the insurance and financial services[21]. In a country where more than 70% of the households use diesel for heating, chaotic wood cutting is observed in inland and mountain rural areas notably in response to higher fuel prices. Earlier observations showed that the forest cover in the Bekaa area has declined dramatically during the last 50 years resulting in intensive erosion of marginal lands [7].

A brief comparison of the current sensitivity to desertification map with the national desertification prone areas map of 2003 [33] shows comparative general trends with fine-tuning of previous assessment

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