Impact of Climate Change on Hydrological Extremes (Floods and Droughts) in the Upper Blue Nile Basin

Abstract Understanding the impacts of climate change on hydrology is crucial for addressing water-related challenges such as water scarcity, flooding, and drought. Measurements provide evidence of climate change and global warming. As a downstream country, Egypt is highly dependent on the water resources of the Nile, where the Blue Nile’s share is the largest of the inflow at Aswan. In the Blue Nile River basin, with some exceptions, most studies generally address two periods in the 21st century for climate change impact evaluation: mid-century (2050s) and end of century (2080s). For these future horizons, the projections of precipitation changes, in previous research, remain uncertain with some indicating increased flow and others predicting decreases. This research assesses climate change impacts on Upper Blue Nile flows using high-resolution data from the COordinated Regional Climate Downscaling Experiment (CORDEX) for the African domain, incorporating multiple Global Circulation Models (GCMs) and Regional Climate Models (RCMs). Hydrological modeling is a critical step in projecting climate change impacts on the Upper Blue Nile flows; thus, it is important that the model be compatible with changing climate parameters. Therefore, the Surface Controlled Hydrologic Model (SCHydro) was modified to account for temperature changes when estimating losses. Results showed both increasing and decreasing trends in Blue Nile flows, depending on the models used. Additionally, the probabilities of flood and drought periods were found to be nearly equal through 2100. These findings highlight the need for adaptable water management strategies to address uncertainties and potential extremes in the basin. Graphical Abstract This graphic abstract presents a detailed analysis of the impact of climate change on hydrology in the Upper Blue Nile Basin, highlighting methodology, results, and conclusions. The methodology integrates climate projections from three Global Climate Models (GCMs) under two Representative Concentration Pathways (RCP4.5 and RCP8.5) from the CORDEX-Africa dataset, bias corrected using the Delta Change Factor method for improved accuracy. the Surface Controlled Hydrologic Model (SCHydro) was modified to consider the change in temperature in determining the losses. The results indicate a significant shift in seasonal discharge patterns, with reduced wet-season flows and increased dry-season flows, exacerbating water availability challenges. The tables and graphs illustrate changes in flow frequency and intensity, revealing an increased occurrence of extreme hydrological conditions. These shifts emphasize the need for adaptive water management strategies to mitigate future risks of floods and droughts. The conclusion stresses the urgency for policymakers and water resource managers to develop sustainable approaches to balance water distribution, ensure agricultural stability, and enhance resilience amidst changing climate conditions.