This study develops a response-based hydrologic model for long-term (continuous) rainfall-runoff simulations over the catchment areas of big rivers. The model overcomes the typical difficulties in estimating infiltration and evapotranspiration parameters using a modified version of the Soil Conservation Service curve number SCS-CN method. In addition, the model simulates the surface and groundwater hydrograph components using the response unit-hydrograph approach instead of using a linear reservoir routing approach for routing surface and groundwater to the basin outlet. The unit-responses are Geographic Information Systems (GIS)-pre-calculated on a semi-distributed short-term basis and applied in the simulation in every time step. The unit responses are based on the time-area technique that can better simulate the real routing behavior of the basin. The model is less sensitive to groundwater infiltration parameters since groundwater is actually controlled by the surface component and not the opposite. For that reason, the model is called the SCHydro model (Surface Controlled Hydrologic model). The model is tested on the upper Blue Nile catchment area using 28 years daily river flow data set for calibration and validation. The results show that SCHydro model can simulate the long-term transforming behavior of the upper Blue Nile basin. Our initial assessment of the model indicates that the model is a promising tool for long-term river flow simulations, especially for long-term forecasting purposes due to its stability in performing the water balance.

Accurate simulation of precipitation over complex terrains such as the Upper Blue Nile Basin (UBNB) is essential for water resource management and climate impact assessments. The UBNB is characterized by complex terrain and convective precipitation systems that challenge the fine-scale climate simulation processes. This research aims to investigate the best precipitation parameterizations in the Regional Climate Model System (RegCM5) simulating different convective and large-scale schemes over the UBNB domain with 10 km resolution. The RegCM5 is driven by the fifth-generation atmospheric reanalysis (ERA5) for the period of (2000–2009) using the hydrostatic dynamical core. The total precipitation simulations of the different calibration scenarios are assessed to select the optimal RegCM5 configuration over the UBNB. Results show that the model succeeds to capture the dominant spatiotemporal pattern of the precipitation, and the Emanuel scheme coupled with Nogherotto-Tompkins (NoTo) reduces the dominant wet bias in the precipitation simulation. The model highlights challenges in reproducing the UBNB's precipitation variability with a moderate to relatively good correlation of precipitation patterns from 0.46 to 0.77, where deficiency in capturing the large-scale circulations, especially the low-level circulations. The research recommended to focus on dynamics advancement and exploring parameterization schemes that enhance the precipitation representation, such as the Planetary Boundary Layer (PBL) in 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.

Accurate simulation of precipitation over complex terrains such as the Upper Blue Nile Basin (UBNB) is essential for water resource management and climate impact assessments. The UBNB is characterized by complex terrain and convective precipitation systems that challenge the fine-scale climate simulation processes. This research aims to investigate the best precipitation parameterizations in the Regional Climate Model System (RegCM5) simulating different convective and large-scale schemes over the UBNB domain with 10 km resolution. The RegCM5 is driven by the fifth generation atmospheric reanalysis (ERA5) for a period of (2000–2009) using the hydrostatic dynamical core. The total precipitation simulations of the different calibration scenarios are assessed to select the most optimal RegCM5 configuration over the UBNB. Results show that the Emanuel scheme coupled with Nogherotto-Tompkins (NoTo) is the most effective parameterization to capture precipitation but reveals significant overestimation with an accepted wet bias of 66 %. The model highlights challenges in reproducing the UBNB's precipitation variability with a moderate to relatively good correlation of precipitation patterns from 0.46 to 0.77. Sensitivity analysis suggests that the interplay between the model's hydrostatic configuration and vertical domain extent significantly influences precipitation outputs, where deficiency in capturing the large-scale circulations. The research recommended to focus on dynamics advancement, and exploring parameterization schemes enhancing the precipitation representation such as the Planetary Boundary Layer (PBL) in Future.

Accurate simulation of precipitation over complex terrains such as the Upper Blue Nile Basin (UBNB) is essential for water resource management and climate impact assessments. The UBNB is characterized by complex terrain and convective precipitation systems that challenge the fine-scale climate simulation processes. This research aims to investigate the best precipitation parameterizations in the Regional Climate Model System (RegCM5) simulating different convective and large-scale schemes over the UBNB domain with 10 km resolution. The RegCM5 is driven by the fifth generation atmospheric reanalysis (ERA5) for a period of (2000–2009) using the hydrostatic dynamical core. The total precipitation simulations of the different calibration scenarios are assessed to select the most optimal RegCM5 configuration over the UBNB. Results show that the Emanuel scheme coupled with Nogherotto-Tompkins (NoTo) is the most effective parameterization to capture precipitation but reveals significant overestimation with an accepted wet bias of 66 %. The model highlights challenges in reproducing the UBNB's precipitation variability with a moderate to relatively good correlation of precipitation patterns from 0.46 to 0.77. Sensitivity analysis suggests that the interplay between the model's hydrostatic configuration and vertical domain extent significantly influences precipitation outputs, where deficiency in capturing the large-scale circulations. The research recommended to focus on dynamics advancement, and exploring parameterization schemes enhancing the precipitation representation such as the Planetary Boundary Layer (PBL) in Future.

Accurate simulation of precipitation over complex terrains such as the Upper Blue Nile Basin (UBNB) is essential for water resource management and climate impact assessments. The UBNB is characterized by complex terrain and convective precipitation systems that challenge the fine-scale climate simulation processes. This research aims to investigate the best precipitation parameterizations in the Regional Climate Model System (RegCM5) simulating different convective and large-scale schemes over the UBNB domain with 10 km resolution. The RegCM5 is driven by the fifth generation atmospheric reanalysis (ERA5) for a period of (2000–2009) using the hydrostatic dynamical core. The total precipitation simulations of the different calibration scenarios are assessed to select the most optimal RegCM5 configuration over the UBNB. Results show that the Emanuel scheme coupled with Nogherotto-Tompkins (NoTo) is the most effective parameterization to capture precipitation but reveals significant overestimation with an accepted wet bias of 66 %. The model highlights challenges in reproducing the UBNB's precipitation variability with a moderate to relatively good correlation of precipitation patterns from 0.46 to 0.77. Sensitivity analysis suggests that the interplay between the model's hydrostatic configuration and vertical domain extent significantly influences precipitation outputs, where deficiency in capturing the large-scale circulations. The research recommended to focus on dynamics advancement, and exploring parameterization schemes enhancing the precipitation representation such as the Planetary Boundary Layer (PBL) in Future.