Modelling extreme precipitation at convection-permitting scale with the regional climate model REMO2020-iMOVE: Insights from the 2021 Ahr Valley flood

In July 2021, Western and Central Europe were hit by intense heavy rainfall caused by cyclone “Bernd”, leading to catastrophic floods in multiple countries. One of the most affected regions was the Ahr Valley in Western Germany, where 135 people lost their lives in the state of Rhineland-Palatinate alone. As global warming continues, such extreme events are expected to become more frequent, highlighting the need for research on their driving factors that are not yet fully understood. Recent advancements in regional climate modelling allow simulations at convection-permitting scales of 1 to 4 km that provide a more realistic representation of extreme precipitation and therefore enhance our understanding of their spatial and temporal characteristics. 

In this study, we aim to simulate the extreme precipitation event of July 2021 with the non-hydrostatic version of the regional climate model REMO2020-iMOVE by dynamically downscaling the ERA5 global reanalysis over the Ahr Valley region to a horizontal resolution of 0.0275° (approx. 3 km). We will explore whether the 3 km resolution provides an added value compared to a 12.5 km resolution, considering previous studies with REMO2020 which have demonstrated improvements in the diurnal cycle of precipitation by using the non-hydrostatic version at convection-permitting scale, but not in the spatial distribution (Pop et al., 2025). The vegetation module iMOVE (interactive MOsaic-based VEgetation) allows for a more precise representation of the land surface and improvements in vegetation-atmosphere interactions, which we will analyse in detail. Further, we plan to investigate the effects of land use and land cover changes on extreme events in a future step. Our findings will contribute to identifying optimized model configurations for more accurate simulation of extreme precipitation events, providing insights for future climate impact assessments and the development of adaptation measures. 

 

Reference
Pop, C., Böhner, J., Hoffman, P., Pietikäinen, J.-P., Rechid, D. (2025). The role of resolution in modeling irrigation effects up to convection-permitting scale. ESS Open Archive. https://doi.org/10.22541/essoar.173655443.36008527/v1