Climate change impacts the small-scale hydropower potential for the Pungwe B hydropower scheme in Zimbabwe using a multi-model climate ensemble.

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Climate change is expected to significantly impact hydropower generation in Southern Africa, particularly for small-scale producers. The objective of this study was to investigate the impacts of climate change on small-scale hydropower potential for the Pungwe B hydroelectric project. The methodology combined hydro-meteorological data, 15 CMIP6 GCMs' climate projections, statistical analyses (Mann-Kendall, Sen's slopes), and HEC-HMS hydrological modelling to simulate streamflow. The impacts of climate change on hydropower potential were determined using trends analysis and Power Potential Duration Curves (PPDC). The downscaled NEX-GDDP-CMIP6 data was processed and analysed using Python programming, employing bilinear interpolation for spatial downscaling and mean bias correction to ensure data consistency and accuracy. The rainfall data from the NEX-GDDP-CMIP6 (NASA Earth Exchange Global Daily Downscaled Projections) was used in hydrological modelling to simulate streamflow and assess climate impacts on hydropower. The HEC-HMS model performed satisfactorily in simulating streamflow with acceptable accuracy (NSE = 0.57, RMSE = 0.70, PBias = 4.25%). Future temperature trends show significant increases under all SSP scenarios (SSP1.26, SSP2.45, SSP5.85), with positive z-test statistics and p < 0.05. The hydropower potential results indicate distinct trends across different Shared Socioeconomic Pathways (SSPs). Under SSP1 (Sustainability), characterized by low population growth, high economic growth, and a focus on sustainability and equality (SSP1.26), a significant majority (80%, or 12 out of 15) of Global Climate Models (GCMs) predict increases in hydropower potential. In contrast, under SSP2 (Middle of the road), marked by medium population growth, medium economic growth, and a continuation of current trends (SSP2.45), a substantial proportion (87%, or 13 out of 15) of GCMs predict declines. Similarly, under SSP5 (Fossil-fuelled Development), characterized by low population growth, high economic growth, and a focus on fossil fuel development (SSP5.85), a majority (73%, or 11 out of 15) of GCMs also predict declines in hydropower potential. ACCESS-CM2 and HadGEM models show the largest declines (-27 MW), while INM-CM5 predicts increases across all scenarios. Hydropower potential predictions varied by Equilibrium Climate Sensitivity (ECS): High ECS groups consistently predicted decreases (with a few exceptions), medium ECS groups showed mixed trends, and low ECS groups predicted increases. These findings imply that climate change will likely have a negative impact on hydropower potential in the region with the degree of impacts dependent on the magnitude of climate change as represented by ECS. Overall, the study highlights climate change's uncertain impacts on hydropower, stressing need for adaptive management and improved climate models.Keywords: ECS, SSP; HEC-HMS; CMIP6, Power Potential Duration Curve, NEX-GDDP-CMIP6.

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