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University of KwaZulu-Natal Pietermaritzburg (2009)

Spatial and temporal extent of land degradation in a communal landscape of KwaZulu-Natal, South Africa

Bangamwabo, Victor Mugabo

Auteur : Bangamwabo, Victor Mugabo

Université de soutenance : University of KwaZulu-Natal Pietermaritzburg

Grade : M.Sc. 2009.

Résumé
Land degradation in communal rangelands is one of the problems that lowers land productivity, a central point for livelihood and economic benefits in rural areas. Therefore, monitoring spatial and temporal extent of land degradation offer a means of understanding the nature and causes of this phenomenon. Land degradation can be quantified by evaluating land cover changes over a period of time. Using five datasets of historical aerial photographs dating back to 1945, the current study employs GIS and Remote Sensing techniques to reconstruct the history of spatio-temporal extent of land degradation in the light of land cover changes and conversion in Okhombe, a communal area in a mountainous region of KwaZuluNatal, South Africa. However, due to the mountainous terrain nature of the area which greatly affects the geometric accuracy of aerial photographs, this study first evaluated the potential of several georectification techniques in order to optimize geometric accuracy for change detection analysis. To achieve this, four different georectification methods were evaluated while the numbers of Ground Control Points (GCPs) used by the models were altered to assess their effects on the georectification accuracy. Of the four georectification methods, the spline transformation method yielded the highest accuracy when the highest number of GCPs was used, and this approach was thus used to georectify the rest of the historical aerial photographs used in this research. Once georectified, major land cover types were interpreted, digitized and mapped for the respective periods. The ‘Landcover Change Modeler for Ecological Sustainability’ in IDRISI was used to analyse landscape changes. Results showed that at a catchment scale, the spatial and temporal patterns of land degradation (with bare soil surfaces as the main indicator) did not change significantly, despite some other land cover types having changed notably due to land use management interventions and other factors. The major trend evidenced with bare soil surfaces was a slight increase that occurred between 1976 and 1992, a period that experienced low rainfall in the region. The results also demonstrated the roles of land cover changes and conversions in influencing patterns of land degradation. Furthermore, the study has also shown how landscape characteristics and effects of land use management such as slope and access gates influence prevalent patterns of land degradation in communal areas.

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