Future Changes in Climate Extremes: Insights from CMIP6 Model Simulations for the Kagera River Sub-basin, Tanzania

This study assesses future changes in the extreme climate regime of the Kagera River sub-basin in Tanzania using multi-model ensembles (MMEs) derived from Coupled Model Intercomparison Project Phase 6 (CMIP6) Global Climate Models (GCMs). Four climate scenarios were considered: SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, for three future periods: 2041–2060, 2061–2080, and 2081–2100. Eight indices from the Expert Team on Climate Change Detection and Indices (ETCCDI), along with the Standardized Precipitation Index (SPI), were used to analyze future changes in temperature and precipitation extremes, as well as drought patterns. The results indicate that monthly and seasonal rainfall will potentially increase by up to 123% and 55%, respectively. The consecutive dry days (CDD) and the number of heavy precipitation days (R10mm) are expected to decrease by up to 133% and 41%, respectively. In contrast, the average precipitation intensity on wet days (SDII) could rise by up to 57%, while maximum one-day precipitation (Rx1day) may increase by up to 127%. Spatial variability in extreme precipitation changes across the sub-basin was also evident. The SPI indicates mixed patterns in the frequency of severe drought events, but no periods of consecutive severe drought years were indicated. Additionally, the results suggest increases in temperature extremes, with the annual maximum and minimum values of daily maximum (TXx, TXn) and daily minimum temperatures (TNx, TNn) all expected to rise in the future. These findings are critical for informing adaptation strategies aimed at mitigating the impacts of climate change in the Kagera sub-basin and the broader Lake Victoria region.