Towards improved Euro-Mediterranean discharge simulations in regional coupled climate models: a comparative assessment of hydrologic performance

Abstract. River discharge into the Mediterranean Sea is a vital component of the regional water cycle, influencing ecological and climatic dynamics. Although some regional coupled models that include a river routing component exist for the Mediterranean region, their performance in reproducing river discharge is poor. This study compares the hydrological routing models CaMa-Flood and WRF-Hydro for discharge simulations into the Mediterranean Sea, with the prospect of future coupling into regional and Earth system models such as ENEA-REG. Evaluating their performance across key basins, this study highlights CaMa-Flood's computational efficiency but underperformance in flow variability and high-flow extremes, contrasted by WRF-Hydro's superior timing and bias reduction, especially after calibration. In fact, results indicate that the calibration improved WRF-Hydro's metrics, including Kling–Gupta Efficiency (KGE) and lag times, underscoring its potential for precise discharge predictions at higher computational costs. These findings offer critical insights for advancing regional coupled Earth system models, enhancing hydrological forecasting, and addressing basin-specific hydrological challenges.