**2.7 Discussion**

The evaluation of climate change's hydrological consequences often necessitates using a hydrological model forced with GCMs under various emission scenarios [52]. This study established the use of the PCR-GLOBWB model for two West African river basins; the Niger river basin and the Hadejia-Jama'are Komadugu-Yobe Basin (HJKYB). The monthly streamflow simulation results of the gauge stations of the two river basins were validated against observed discharge (GRDC) using five performance evaluation metrics were. The output of GCMs from the first phase of the ISI-MIP was adopted to investigate the response of streamflow seasonality to climate change. The PCR-GLOBWB was shown to be very applicable over the two basins. Its PBIAS, NSE, RSR, r2 and KGE values ranged from −25 to 0.8, 0.6 to 0.8, 0.62 to 0.4, 0.62–0.88, and 0.69 to 0.88, respectively, which were within the acceptable limits [45], as shown in **Table 2**.

According to the results of the multi-model median regarding climate change, climate change impacted the temporal pattern of future river discharge in the river basins. The late start of the rainy season concluded in this work has been reported by previous studies [13, 48–50, 53]. Streamflow of the three rivers in combined HJKYB, the Yobe, Jamaare and the Hadejia, is controlled by precipitation. Genthon et al. [54] reported the climatic influence on discharge in this basin. Across the two basins, our findings indicate that climate change exacerbates the seasonality pattern already present. The basins influenced by precipitation exhibit a continuous increase in streamflow volumes during the later part of the high-flow season. In the Niger basin, climate change significantly affects the volume of streamflow seasonality (indicated by SI). In the four rivers, projected river discharge seasonality is amplified under the high-end emission scenario (RCP8.5); our findings support decisions on the potential advantages of reduced greenhouse gas emissions for the streamflow dynamics. It must be stressed that our analysis focused exclusively on the effects of climate change on streamflow regimes. Population expansion and economic development envisaged for the future are expected to raise human demand for water resources, potentially intensifying their interference with the streamflow regime. The consequences of these could outweigh the climatic changes examined in this study.
