Abstract. In the 1960s, Lake Chad was the world’s sixth largest water body, which has since shrunk dramatically from a surface area of 25,000 km² to only 2,000 km² in the following 40 years. In the present study, hydro-climatic variability in the Chari-Logone, Komadugu-Yobe, YENG (Yedseram, El-Beid, Ngadda and Gubio basins) as well as Lake Fitri basins and decreasing streamflow to Lake Chad due to climate variability and human activities were separated and quantified using trend analysis, change point analysis, and hydrological approach, for the period of 1951–2015. The results showed very strong signals (α = 0.001) of increasing trend in mean temperature, with an average increase of 1.4 °C, and very weak (α = 0.1) to strong (α = 0.01) decreasing signals in precipitation, with an average decrease of 15 %. In case of streamflow to Lake Chad, very strong decreasing trends were observed, showing 67 % reduction for the whole period. The north-eastern parts were most affected parts in case of increasing temperature and decreasing precipitation. Decreasing flow due to both climate variability and human activities were ranged from 34 % to 45 % in different decades, from 1972 to 2013. On the whole, a 66 % of total decline in streamflow was observed due to human activities and 34 % due to climate variability. Most reduction in streamflow (59 %) due to climate variability was explored only during 1982–1991 because a devastating drought was occurred during this period. Since human activities caused most reduction in streamflow to Lake Chad than climate, inflow to the lake can be improved by reducing or properly managing the human activities and using sustainable water resources management.