Circulation versus background warming: drivers of European hot and wet extremes since 1980

Changes in regional extreme weather and climate events intensify under human-induced global warming. We unravel the drivers and mechanisms driving historical European hot and wet extremes through high-resolution regional climate model simulations, using the ICOsahedral Nonhydrostatic model in climate limited area mode (ICON-CLM). Specifically, we disentangle the contributions of the large-scale weather situation (dynamic conditions) and the local temperature and humidity (thermodynamic conditions) in heatwaves and heavy precipitation events over Europe since 1980.

To this end, we drive ICON-CLM simulations over Europe using boundary conditions from a global model constrained to follow the observed large-scale circulation. We run two sets of experiments: one where both the regional and global model use historical forcing, and one where both use pre-industrial greenhouse gas and aerosol concentrations, while the large-scale circulation remains identical. The difference between these simulations isolates the thermodynamic contribution of anthropogenic climate change to extreme events. Moreover, we perform a simulation with climatological soil moisture, to further quantify the role of land-atmosphere interactions for climate extremes. This model chain and experimental design allows us to disentangle the dynamic and thermodynamic drivers of hot and wet extremes at high resolution, resolving mesoscale processes that are especially critical to heavy precipitation events. It also enables a process-based attribution of all major European extreme events since 1980, moving beyond the case-study paradigm that dominates current research.