Urban flooding is considered one of the hazardous disasters in metropolitan areas, especially for those located in arid regions. Due to the associated risks of climate change in increasing the frequency of extreme rainfall events, climate-induced migration to urban areas leads to the intensification of urban settlements in arid regions as well as an increase in urban expansion towards arid land outskirts. This not only stresses the available infrastructure but also produces substantial social instability due to unplanned urban growth. Therefore, this study sheds light on the main factors that are increasing the flood risk, through examining the consequences of rapid urban growth and the performance of drainage networks on urban flood volumes and comparing it with the effects induced by climate change on the surface runoff. The effect of urbanization is assessed through land use maps showing the historical urbanization conditions for the past 30 years, while considering the role of urban planning and its effect on exacerbating surface runoff. Six climate projection scenarios adopted from three Global Climate Models under two Representative Concentration Pathways (4.5 and 8.5) during the period (2006–2020) were compared to ground observed rainfall data to identify which climate scenario we are likely following and then evaluate its effects on the current rainfall trends up to the year 2050. The significance of the drainage design in the mitigation or increase of surface runoff is evaluated through capacity-load balance during regular and extreme storms. It is found that using impervious surfaces coupled with poor planning causing the blockage of natural flood plains led to an increase in the total runoff of about 180%, which is three times more than the effect induced by climate change for the same analysis period. Climate change decreased the intensities of 2- and 5-year rainfall events by 6% while increasing the intensities of extreme events corresponds to 100-year by 17%. Finally, the urban drainage had a distinguished role in increasing surface runoff, as 70% of the network performed poorly during the smallest rainfall event of 2-year return period. The study emphasizes the urgency to re-evaluate the existing and future urban drainage design approach: although urban development and climate change have inevitable effects on the increase in urban flood volumes, it could be alleviated through improved infrastructures.

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.

Groundwater is the main water source in arid climate regions. Climate change and extensive groundwater exploitation will stress the groundwater resources in the upcoming decades. Therefore, groundwater quantity and quality should be assessed. In this study, we focused on groundwater quantity, including recharge and storage (using groundwater level as an indicator) to predict system vulnerability. The northern portion of El-Qaa Plain was chosen as a case study because the aquifer is coastal, arid, over-exploited, and naturally replenished via seasonal precipitation events. To project groundwater recharge under climate change and future exploitation, Water and Energy Transfer between Soil, Plants, and Atmosphere under quasi-steady State (WetSpass) was applied. Modular Finite Difference Groundwater Flow Model (MODFLOW) was utilized to project the groundwater level. Future climate ensembles were acquired from Regional Climate Models (RCMs) of Coordinated Regional Downscaling Experiment (CORDEX) datasets for the EURO 11 domain. The ensembles were bias-corrected using the Delta Change Factor (DCF) method. The results indicate that groundwater resources will be severely affected by climate change, as recharge might drop by nearly 35% to 75% during 2071–2100 for moderate and severe change ensembles. The mean groundwater level might decline by around 7–8 m by 2100 for the same ensembles. Regarding over-exploitation, the maximum drawdown will rise to approximately 16 m (no change in abstraction rate), to 36 m (increase in abstraction rate), and 7 m (decrease in abstraction rate). The results might aid decision-makers and stakeholders developing sustainable water resource management plans for the area.

Hydrogeological parameters are very uncertain to specify in the groundwater flow models. Hence, it is important to specify a range for these parameters to be further utilized by the groundwater model users. In El-Qaa Plain, previous researchers have determined the hydrogeological parameters such as transmissivity, hydraulic conductivity, and mean annual recharge rate using geophysical methods, pumping tests, hydrological models, and groundwater flow models. However, they are also limited to specific locations and do not spatially distribute. In this paper, an effort has been accomplished to specify a specific range for the aquifer hydrogeological parameters using inverse groundwater modeling taking into account the spatial heterogeneity. These ranges could be taken into consideration during modeling groundwater flow. Hence, a finite-difference groundwater flow model has been applied using the ModFLOW model. Regularized pilot points method (RPPM) has been chosen as an inverse modeling technique to specify the accurate values of the aquifer parameters. Model-independent parameter estimation and uncertainty analysis (PEST) has been utilized to estimate the parameters. The results show that the geometric mean of the hydraulic conductivity in the study area ranges from proximity 1 to 2 m/day. Additionally, the geometric mean of the transmissivity ranges from nearly 200 to 500 m²/day. A relationship between the mean annual recharge rate and hydrogeological parameters has been determined. Besides, maps have been generated showing the spatial heterogeneity of the hydraulic conductivity. These maps could be further utilized by groundwater flow modelers to predict the potential of groundwater flow and pollution in the future.

The Upper Blue Nile Basin (UBNB), which contributes about 60% to the annual Nile flow, plays a critical role in the Nile water management. However, its complex terrain and climate create significant challenges for accurate regional climate simulations, which are essential for climate impact assessments. This study aims to address the challenges of climate simulation over the UBNB by enhancing the Regional Climate Model system (RegCM5) with its new non-hydrostatic dynamical core (MOLOCH) to simulate precipitation and temperature. The model is driven by ERA5 reanalysis for the period (2000–2009), and two scenarios are simulated using two different schemes of the Planetary Boundary Layer (PBL): Holtslag (Hol) and University of Washington (UW). The two scenarios, noted as (MOLOCH-Hol and MOLOCH-UW), are compared to the previously best-performing hydrostatic configuration. The MOLOCH-UW scenario showed the best precipitation performance relative to observations, with an accepted dry Bias% up to 22%, and a high annual cycle correlation >0.85. However, MOLOCH-Hol showed a very good performance only in the wet season with a wet bias of 4% and moderate correlation of ≈0.6. For temperature, MOLOCH-UW also outperformed, achieving the lowest cold/warm bias range of −2% to +3%, and high correlations of ≈0.9 through the year and the wet season. This study concluded that the MOLOCH-UW is the most reliable configuration for reproducing the climate variability over the UBNB. This developed configuration is a promising tool for the basin’s hydroclimate applications, such as dynamical downscaling of the seasonal forecasts and future climate change scenarios produced by global circulation models. Future improvements could be achieved through convective-permitting simulation at ≤4 km resolution, especially in the application of assessing the land use change impact.