Assessment of land-cover changes in a sub-catchment of the Oti basin (West Africa) A case study of the Kara River basin

Abstract

This study is presenting results from the analysis of land-cover dynamics in the Kara River basin from 1972 to 2000 using remote sensing and geographic information system (GIS) techniques. Multi-temporal satellite images – Landsat MSS (1972), TM (1987) and ETM+ (2000) were processed using object-oriented classifi cation and postclassifi cation comparison methods. The classifi cation results showed a good agreement with overall accuracies of 77.1% for 1972, 85.34% for 1987 and 88.22% for 2000, the respective Kappa statistics being 0.7, 0.81 and 0.85. Change assessment showed that the basin has experienced important changes in land cover with signifi cant decrease in natural vegetation. Agricultural extension and deforestation appear to be the dominant driving forces. In fact, agricultural land has doubled between 1972 and 2000 by increasing from 19.45% to 43.59% of the total basin area while savannah decreased from 63.41% to 45.19%. Forest land increased by 1.63% from 1972 to 1987 but showed a decrease of 5.87% from 1987 to 2000, while woody savannah decreased by 3.59% and human settlements increased during the same period. The analysis of land cover transition showed that important changes have occurred between 1987 and 2000. The results of this study will be useful for follow-up research such as hydrological and landscape processes modelling in the basin but also many applications including the biomass assessment for greenhouse gases inventories, the REDD+ (Reducing emissions from deforestation and forest degradationplus) project, the national programs for protected areas redefi nition, vegetation resources conservation and sustainable land management, the vulnerability and adaptation studies etc. . Nevertheless, further investigation integrating climatic, hydrological, spatial statistics and socio-economic models would help to better understand and quantify the relationships between different driving forces and their contributions to the changes.