Evaluation of RegCM5 for Simulating Aerosols–Precipitation Interactions over Saudi Arabia

This study aims to assess the ability of the RegCM5 regional climate model to simulate aerosol effects on precipitation distribution over the Kingdom of Saudi Arabia during 2003 -2020. The methodology is based on two main experiments: one without aerosols (dust, sea salt, black and organic carbon, and sulfates) and one with full aerosol interactions, using CAMS reanalysis data as the reference. Model performance was assessed at five stations distributed across the Kingdom (Riyadh, Jeddah, Dammam, Abha, Tabuk) using correlation coefficient, bias percentage, and root mean square error. The results show that RegCM5 successfully reproduces the general sign of aerosol–precipitation relationships; a positive correlation with dust exceeding 0.7 at Riyadh and Dammam due to proximity to local and transboundary dust sources, a positive correlation with sea salt exceeding 0.85 at Jeddah due to the Red Sea influence, and a negative correlation with black and organic carbon reaching -0.75 at Abha and Riyadh. However, the model exhibits spatial bias in simulating the magnitude of these relationships, particularly in the southwestern region (Abha, Jazan) where moisture sources interact with natural and anthropogenic aerosols. This may be due to limitations in the parameters for aerosol–cloud interaction in the RegCM5 model, and also to the lack of accurate representation of local emissions of black and organic carbon. We conclude that RegCM5 captures the general features of aerosols' impacts on precipitation over Saudi Arabia, but requires improvements in wet removal parameters and spatial resolution to accurately reflect the climatic variability and local sources of aerosols evident in CAMS reference data.