Impact of cumulus parameterizations on the simulation of the september 2019 torrential rainfall event over the southeast of the Iberian peninsula

Abstract The Western Mediterranean Basin is positioned between the cold Atlantic region and the subtropical high-pressure belt, creating a distinctive climate characterised by irregular heavy rainfall. These extreme precipitation events are often associated with cut-off polar fronts interacting with warm, moisture-laden air masses from the Mediterranean Sea, triggering intense convective storms. This study examines one of the most significant flood events in the region’s recent history, which occurred between 11 and 14 September 2019 over the Southeast of the Iberian Peninsula. To enhance our understanding of the processes driving such extreme weather, we employed the WRF model to evaluate different cumulus parameterization schemes. Specifically, we aimed to identify which scheme most accurately reproduces observed precipitation and cumulus formation and to assess the influence of cumulus parameterization activation in the higher-resolution grid on model performance. Our findings highlight the crucial role of orography in precipitation estimation, as it significantly influences convective initiation. Despite the high spatial resolution of the inner grid (3 km), results indicate that parameterized convection remains beneficial for resolving sub-grid processes. Among the tested schemes (Kain-Fritsch, Betts-Miller-Janjic, and Grell-Freitas), scale-aware parameterizations, such as Grell-Freitas, exhibited the best performance in high-resolution models due to their ability to dynamically adjust convective processes to the model’s spatial scale. The insights gained from this study contribute to a better understanding of extreme weather dynamics in the Mediterranean region, offering valuable guidance for improving the modelling and forecasting of torrential convective storms in the region.