Aerosol effects on convective storms under pseudo-global warming conditions: Insights from case studies in Germany

Abstract

Germany is heading toward a future with warmer temperatures due to climate change, and potentially cleaner air from electrification and stricter emission regulations. But how will these evolving environmental conditions affect severe convective storms? This study addresses this question by simulating three supercell events in high resolution using the ICOsahedral Non-hydrostatic (ICON) model. The events observed during the Swabian MOSES field campaigns in 2021 and 2023 are analysed using the pseudo-global warming approach to assess their evolution in a warmer climate. The effects of aerosols on clouds and precipitation were considered using a two-moment microphysics scheme in four temperature rise scenarios, providing detailed insights into the underlying microphysical mechanisms. The results indicate that higher temperatures generally enhance convection, resulting in more intense convective cells, increased precipitation amounts, and more extreme rainfall and hail events. Additionally, warmer conditions increase the likelihood of supercell formation and more intense mesocyclones. In some cases, precipitation increases exceed 7 % K-1, indicating super-Clausius-Clapeyron scaling and suggesting that additional dynamical and microphysical processes amplify rainfall beyond thermodynamic expectations. An important finding is that hailstones grow larger under lower cloud condensation nuclei (CCN) concentrations, and the area affected by large hail expands by up to 400 %, indicating growing severity and reach of hail events. In addition, lower CCN concentrations are associated with a reduced cold-to-warm rain formation ratio and decreased precipitation efficiency. These aerosol-related effects appear largely independent of temperature, showing consistent patterns across all simulated warming scenarios. These findings indicate the intensity of severe weather events, such as convective storms and flash floods, may increase in a future climate.