Extent of Lake Tana’s Papyrus Swamps (1985–2020), North Ethiopia

Lake Tana is the largest freshwater lake in Ethiopia and is the source of the Blue Nile. The lake shorelines and those of its tributary river, Gilgel Abay, are characterized by the occurrence of extensive papyrus swamps ( Cyperus papyrus L) . While such papyrus swamps are highly recognized for their outstanding ecological and economical importance, their historical and current spatial distribution and size in the Lake Tana sub basin have not yet been systematically assessed. The primary goal of this study was to estimate the spatial distribution and temporal dynamics of papyrus swamps in the Lake Tana sub basin at five-year intervals over a period of 35 years (1985–2020). Our analyses revealed that the total surface area of the papyrus swamps in the study area declined by almost 55% (from 152 km² to 64 km²) during the last 35 years. The small patches of papyrus swamps that existed in the northern and eastern parts of the study area prior to the 1990s appear to have disappeared in recent years as well. Our data suggest that the strong decline of papyrus swamps mainly resulted from the expansion of crop farming, livestock overgrazing, drainage, and biomass overharvesting, all of which are increasing over time.