ASSESSING FUTURE CLIMATE CHANGE IMPACTS ON HYDROPOWER GENERATION IN THE SHIRE RIVER BASIN-MALAWI

Abstract

The global hydropower sector relies on surface water flows of substantial and predictable volume, which makes it vulnerable to climate change. This study focused on assessing the risks posed by climatic factors on river flow regimes and their impact on future hydropower production in the Shire River Basin. The study employed Mann-Kendall test and Sen's slope estimator to detect climatic trends in the time series data and estimate the magnitude of the trend. Future river flow regimes were analysed using HEC-HMS by integrating future climatic projections data from CIMP6 models under ssp2-4.5 and ssp5-8.5 scenarios. The performance of the climate models was evaluated using the Coefficient of Determination (R2), Nash Sutcliffe Efficiency (NSE), Root Mean Square Error (RMSE) and Percent Bias (PBIAS), Including a Pearson Matrix Scatter Plot for the historical data to check how well the models represented the study area. Similarly, the hydrological model’s performance was assessed using the NSE and R2 of the simulated flows against the observed. Flow Duration Curves were used to assess the future impacts of the river flow regimes on hydropower generation at low flow regimes. Mann-Kendall results showed a significant increasing rainfall trend for 68% of the stations in the basin. Minimum temperatures did not show any significant trends, whereas all stations showed a significant increasing trend for maximum temperatures. Both climate and hydrological models showed good performance in representing observed data. Future rainfall patterns indicated a general increase of 13-28% in wetter months, and a decrease in drier months of 3-8% under all scenarios, with a more notable increase in the 2030-2064 period under ssp5-8.5. Future river flow regimes took a similar pattern as rainfall, with a marked increase in all scenarios, but particularly very high under ssp5-8.5 but showing lowest flows in the drier months in the 2030-2064 period. High flows highlight the potential of flooding events in the basin which could affect the hydropower equipment, but could also increase the potential of the sector. Frequency analysis on the low flows, shows susceptibility of the hydropower sector to climate change as it is projected to cause low power generation. The findings from this study underscore the importance of diversifying the energy mix, while protecting the hydropower infrastructure from potential flooding events