Optimizing Precipitation Parameterizations in Regional Climate Model (RegCM5): A Case Study of the Upper Blue Nile Basin (UBNB)

Abstract. 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.