Geospatial assessment of land degradation: a case study of Selebi Phikwe and Mmadinare area, Botswana

Abstract

Botswana is one of Sub-Saharan Africa drylands that are prone to land degradation. Land degradation is among others linked to pressure from conflicting land uses and cyclical droughts. This study aimed to assess land degradation in Bobirwa sub-district in the Selebi Phikwe and Mmadinare area that has been noted to experience resource depletion. The study assessed the spatial and temporal dimensions of land degradation and its drivers over a period of 48 years (1971 to 2019), applied decrease in vegetation cover as the main indicator in addition to others such as bush encroachment. Evidence was gathered using geospatial information technology, social and biophysical surveys and from secondary data. Image classification, vegetation indices and thermal radiation were applied to detect and map land degradation as appropriate using 1971 Air photographs, 1990 Landsat Thematic Mapper (TM), 2010 Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and 2019 Landsat 8 Operational Land Imager (OLI) imagery. The established evidence was integrated using Geographical Information Systems (GIS) and related to rainfall, livestock rearing, human population, and land-use pressure, especially mining activity. Four levels of degradation according to severity were established; highly degraded; moderately degraded; slightly degraded and non-degraded. Results showed that by 1971 the study was dominated by the non-degraded level of degradation but in subsequent years the area remained predominantly under moderately degraded. Highly degraded areas were confined to drainage systems and the vicinity of settled areas. These results formed the basis for modelling the likely status of land degradation by 2030. The study concluded that mining and resulting land-use pressure, especially overgrazing and deforestation intensified land degradation during periods of below-average rainfall. These findings will contribute further to the discussions on the role of human and climatic factors on the process of land degradation in semi-arid lands and the need to put in place appropriate management systems.