Study of the fluctuation of the NDVI in the Casamance River Basin upstream of Kolda using remote sensing data: what impact on flow?

Abstract

Changes in land use and land cover have attracted considerable scientific interest in recent years because of their marked influence on hydrological cycles. In the tropics, widespread vegetation degradation and changes in land use that occurred from the 1970s onwards have affected the hydrological dynamics of catchments. In this study, land cover changes in the Casamance catchment upstream of Kolda in recent years were analysed and their role in hydrological evolution was estimated. These changes had occurred in environmental conditions between 1987 and 2018. Remote sensing and geographic information system (GIS) techniques were used to monitor changes in the basin as well as changes in NDVI values. Landsat 5 and 8 satellite images were used respectively. The extraction of land cover in the basin was carried out through the application of unsupervised nesting classification processes. The results indicated that a regression of forest cover in the Casamance River Basin upstream of Kolda and the classification of the area into seven main land categories (forest, savannah, slash-and-burn, cultivated areas, habitat, plantations and water) was significant. Like rainfall, the flow rates, which declined during the 1980s, increased from the 2000s onwards, although the trend was not significant. This increase in runoff is the result of vegetation degradation and increased rainfall. The results highlight the importance of integrating land use information into assessments of water availability in a region where water is a strategic resource.

Keywords: Casamance Basin Basin, GIS, NDVI, Remote Sensing, Supervised Classification