Recent dynamics in sediment connectivity in the Ethiopian Highlands

Sediment connectivity indexes serve as a diagnostic tool for investigating the overall hydro-geomorphological functioning. The primary factors influencing sediment connectivity are rainfall and changes in land cover. For the period 1995–2016, we investigated changes in sediment connectivity in two ca.1000 km² catchments located in the Ethiopian Highlands and evaluated the potential sediment sources of the catchment. These catchments are characterized by severe land degradation and high sediment yields. The sediment connectivity of the catchments was computed using SedIn-Connect, incorporating variables such as a digital elevation model, rainfall erosivity, soil erodibility, surface roughness, cover management, and surface runoff to formulate the weight factor. Rainfall variability was calculated using TAMSAT data, and land cover maps were derived using Landsat data in Google Earth Engine. The findings show substantial spatial variability in sediment connectivity across the two catchments. The modified index of connectivity value has a positive correlation with sediment yield from two stations whereby the sediment connectivity is higher in the Gumara Catchment than in the Rib Catchment. In both catchments, bare land, cropland, shrubland, and grassland exhibited higher connectivity, whereas forest and rural settlements displayed lower connectivity. Croplands registered the most pronounced increase in connectivity, mirroring similar trends observed in shrublands and grasslands. Conversely, forested areas demonstrated relatively stable connectivity patterns. Notably, croplands nestled in steep slopes and proximate to rivers emerged as potential sediment sources capable of influencing sediment connectivity within the two catchments.