Monitoring of Dryland Vulnerability by Remote Sensing and Geoinformation Processing: Case of Wadi Bouhamed Watershed (Southern Tunisia)

Abstract

Land degradation (LD) has become a crucial issue with both environmental and socio‐economic implications. Natural forces, through periodic stresses of extreme and persistent weather events, and human use and abuse of vulnerable areas, jointly affect LD dynamics, creating negative feedbacks for the ecosystem equilibrium. Spatial assessment of environmental phenomena at regional scale involves the analysis and fusion of multiple, complex, multidisciplinary, and large‐scale information. It is thus important to develop cost effective methodologies to assess and monitor dryland conditions. Remote sensing data and geoprocessing are currently widely tested for this purpose as repeatable and spatial cost-effective ideal tool. Meanwhile, standardized techniques and operational procedures still need to be developed to evaluate land degradation and desertification in the arid areas of Mediterranean regions. Changes in surface properties can be detected through remote sensing data analysis. The main sources of information for the large scale monitoring of soils and vegetation is nowadays derived from satellite imaging. Several indices based on visible near-infrared (VNIR) and short-wave infrared (SWIR) reflectance spectrum are used to produce qualitative and quantitative studies of land degradation and desertification through biological, geophysical and chemical properties description. The general objective of this chapter is to present an overview of dryland degradation and to discuss geo-information and remote sensing data analysis as a support tool for the assessment and monitoring of dryland vulnerability in Southeastern Tunisia. Land Use Land Cover (LULC) changes in the Wadi Bouhamed catchment during 1988–2000 and 2000–2011 periods have been evaluated by soil and vegetation radiometric indices (Normalized Difference Vegetation Index-NDVI; Brightness Index-IB) using LANDSAT TM et ETM + images. Data highlighted that desertification is extending downstream the watershed with a sand movement phenomenon. This is mainly explained by long drought events observed since 1988 enhanced by human practices. Starting from the ’80, modification of agricultural activities intensification on the one hand and marginal land abandonment on the other had caused severe environmental impacts, including the increase in land degradation risk.