Impact of anthropogenic changes and rainfall variability on river discharge in tropical central Africa

Abstract

Abstract Climate variability and anthropogenic changes are key factors that influence river flow variability. However, understanding the simultaneous impact of these factors on flow variability remains limited in most parts of the world including central Africa. To shed light on this issue, the objective of this study is to investigate the effects of rainfall variability and anthropogenic changes on river discharge in the Benoue and the Logone river basins over the last 7 decades (1950–2018). To achieve this goal, hydro-meteorological data from these basins were analyzed using the Pettitt test. Likewise, land use change in these basins was also analysed using supervised classifications of Landsat satellite images over different periods (1987 and 2018). Our results show that the Sahel drought that occurred towards the end of the 1960s affected the Benoue and Logone basins, with remarkable persistence in streamflows. Negative rupture was observed in the hydro-meteorological timeseries of these basins at annual time step in 1970-71. The deficits associated with this rupture are estimated at -7% for rainfall, and − 28% for river flows. The wet season shows similar developments. However, from the 1990s onward, there has been a significant increase in the mean annual flows of the Benoue river, which coincides with that of the rainfall during the same decade. This increase over the recent decades could also be expected in response to an increase in impervious surface areas (ISA) in the catchment area, which could compensate the deficit generated by the post-1990s rainfall deficit through increasing in runoff. Since the filling of the Lagdo dam in 1983, an increase in all ranges of minimum flow, as well as an increase in the variability of extreme flows, has been detected. These results could be used for long-term planning of water demand and use in these basins, as well as for improving future simulations of the flow of these rivers. It also shows that due to the non-linearity of the rainfall-runoff relationships, it is very important to maintain observation networks operational, as the current situation might still evolve in the near future, requiring new adaptations for social response.