Hydroclimatic variability manifests as abrupt shifts, trends, runs, and recurrent cyclical phenomena, collectively referred to as components. In this article, we tested for the presence and magnitude of each component in the Niger Basin (West Africa), using the 0.5° by 0.5° gridded annual rainfall and temperature data produced by the Climate Research Unit (CRU) at the University of East Anglia, UK, for the period 1901–2006. The streamflow data was also analysed for different sub‐basins of the Niger Basin. Abrupt shifts were tested using a Bayesian and nonparametric approach. Trends were analysed using the Mann‐Kendall trend test. Runs were extracted for dry, neutral, and wet conditions, simulated 1000 times based on the skew normal distribution, and used to investigate various run characteristics. Cyclical behaviour was investigated using continuous wavelet analysis. The results show that an abrupt change point occurred in 1969 in the rainfall and streamflow (but not temperature) time series in all subwatersheds of the Niger Basin. The magnitude of the shift in the mean rainfall varied between 16 and 24%. The temperature time series exhibit strong positive trends in all watersheds. Post change point, the rainfall and streamflow time series show positive, though statistically non‐significant trends at α = 0.1. In contrast, disregarding the change point, all subwatersheds show significant negative trends at α = 0.05 and the maximum run lengths are about 4 years long for both dry and wet conditions. Finally, wavelet analysis showed that both rainfall and streamflow in the Niger Basin fluctuate on cycles that are predominantly 2–4 years long, with a few occurrences in the 6–8 years range. Wavelet activity diminished noticeably when a series appeared strongly dominated by trends. The results provide a more comprehensive view of climatic variability than would be obtained from only one or a few components.

The Abdus Salam International Center for Theoretical Physics (ICTP) version 4.4 Regional Climate Model (RegCM4) is used to investigate the rainfall response to cooler/warmer sea surface temperature anomaly (SSTA) forcing in the Indian and Atlantic Oceans. The effect of SSTA forcing in a specific ocean basin is identified by ensemble, averaging 10 individual simulations in which a constant or linearly zonally varying SSTA is prescribed in individual basins while specifying the 1971–2000 monthly varying climatological sea surface temperature (SST) across the remaining model domain. The nonlinear rainfall response to SSTA amplitude also is investigated by separately specifying +1K, +2K, and +4K SSTA forcing in the Atlantic and Indian Oceans. The simulation results show that warm SSTs over the entire Indian Ocean produce drier conditions across the larger Blue Nile catchment, whereas warming ≥ +2K generates large positive rainfall anomalies exceeding 10 mm·day⁻¹ over drought prone regions of Northeastern Ethiopia. However, the June–September rainy season tends to be wetter (drier) when the SST warming (cooling) is limited to either the Northern or Southern Indian Ocean. Wet rainy seasons generally are characterized by deepening of the monsoon trough, east of 40°E, intensification of the Mascarene high, strengthening of the Somali low level jet and the tropical easterly jet, enhanced zonal and meridional vertically integrated moisture fluxes, and steeply vertically decreasing moist static energy. The opposite conditions hold for dry monsoon seasons.