Assessing the impact of human activities and rainfall variability on the river discharge of Komadugu-Yobe Basin, Lake Chad Area

The impact of human activities and rainfall variability on river discharge is of main concern for policymakers in the Komadugu-Yobe Basin (KYB), Lake Chad area. The KYB is of strategic importance because its rivers contribute significantly to the recharge of Lake Chad whose shrinkage has been of concern to policymakers and the international society. This study investigates the variations in river discharge of the KYB as a result of the contributory effects of rainfall variability and human influences, using daily rainfall and discharge data between 1971 and 2013. In order to partition the impacts of rainfall variability and human activities on river discharge, breakpoints related to abrupt environmental changes caused by human activities are identified using the generalized variance (GV), double mass curve (DMC) and the wavelet spectral methods. Breakpoints are found in 1974 and 1993, which correspond to times when major dams in the basin became operational. These breakpoints may also be related to LULC changes. The land-use land-cover (LULC) analysis shows an increase in bare surface, plantation, settlements and water bodies from 1975 to 2013, in association with a decrease in the forest and grassland coverage. Overall, the mean discharge between the pre-break and post-break periods increased by 24%. This increment in discharge was caused by approximately 50% rainfall variability and 50% human activities. Hence, the effects of human activities appear to be as important as the effect of natural rainfall variability on the river discharge changes in the KYB.