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University of Padova (2010)

Monitoring desertification in Sudan using remote sensing and GIS

Dawelbait, Mona Abdelhafeez Ahmed

Titre : Monitoring desertification in Sudan using remote sensing and GIS

Auteur : Dawelbait, Mona Abdelhafeez Ahmed

Université de soutenance : University of Padova

Grade : Tesi di dottorato (PhD) 2010

Résumé
Remote sensing technology has long been suggested as a time and cost efficient method for observing dryland ecosystem environments, monitoring land cover degradation and characterizing the dynamism of sand dunes. The meaning and value of remote sensing data were enhanced through skilled interpretation, in conjunction with conventionally mapped information and ground-collected data. Spectral Mixture Analysis (SMA) has proved to be a powerful technique to monitor land cover degradation in arid and semi-arid areas. Three Landsat images, acquired in 1987, 1999 and 2008, were analyzed to evaluate desertification processes in three different ecological zones in Sudan (North Kordofan, River Nile and Northern state). Spectral Mixture Analysis (SMA) was adopted using endmembers spectra derived from the image. Multitemporal comparison techniques (visual interpretation and change vector analysis) were applied to estimate the long-term desertification/re-growing and to emphasize land cover variation over time and in space. Site-specific interactions between natural processes, climate variation and human activity played a pivotal role in desertification ; however their interaction was varied according to the ecological zone. In North Kordofan (savannah), desertification significantly prevailed over vegetation re-growth, particularly in areas around rural villages over the last 21 years. Changes in land use and mismanagement of natural resources, mainly caused by deforestation to supply wood for domestic use and overgrazing, were the main driving factors affecting degradation. More than 120,000 km2 were estimated as being subjected to a medium-high desertification rate. Conversely, the reforestation measures, adopted by the Sudanese Government in the last decade and sustained by higher rainfall, resulted in low-medium re-growth conditions over an area of about 20,000 km2. In River Nile (valleys in semi-desert), extreme condition of desertification affected the valleys in the site. Desertification affected an area of 24,482 km2 as extreme condition and re-growth condition in low status was 1,193 km2 while most of persistence condition (71,298 km2) was desert area. Drought and climate variation with the assistance of mismanagement of natural resources were the factors caused desertification, however, human activities were played minor role. In this site the soil is highly vulnerable to wind and water erosion and it was highly increased in 2008. Irrigated agricultural projects were clearly recognized in Northern State (Valley in desert), with an areas of 28,761 km2 in low condition. The area affected by desertification was 98,275 km2 (7,962 km2 high, 56,075 km2 medium and 34,239 km2 low) with 76.40% percentage of the total area. The agricultural projects were at high risk since they were surrounded by desertified areas. Site-specific strategies which take into account the interactions of the driving factors at local scale are thus necessary to combat desertification, avoiding any implementation of untargeted measures. In order to identify the soundest strategies, high-resolution tools must be applied. In this study the application of SMA to Landsat data appeared to be a consistent, accurate and low-cost technique to obtain information on vegetation cover, soil surface type, and identify risk areas.

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