Thermodynamic drivers intensify future European frontal precipitation extremes, while frontal dynamics remain largely unchanged

Atmospheric fronts are a key driver of intense and extreme precipitation across the mid-latitudes, which is projected to increase under global warming. Understanding the physical drivers of these changes is essential to improve confidence in climate projections.

Here, we analyze projected seasonal changes in heavy and extreme frontal precipitation events over Europe using the CMIP6 and EURO-CORDEX ensembles, combining event frequency analysis with frontal composite cross-sections to assess underlying thermodynamic and dynamic processes.

First, we evaluate the representation of fronts in the CMIP6 and EURO-CORDEX ensembles, using ERA5 as a reference. While synoptic-scale conditions are well represented across models, mesoscale gradients and circulation patterns exhibit a pronounced sensitivity to grid spacing, especially impacting the representation of cold fronts and their associated precipitation.

Future projections show an increase in the number of heavy frontal precipitation events by up to 50 % per degree of global warming, while extreme events more than double per degree. Large-scale circulation changes account for most regional reductions in frontal extremes, but contribute only weakly to the widespread increases. Thermodynamic changes, however, dominate the intensification of extremes. Increases in specific humidity are the primary driver of more intense events, while changes in the frontal circulation are minimal, likely because a more stable atmosphere counteracts potential strengthening from enhanced latent heat release.

These results highlight the dominant role of thermodynamic processes in future frontal precipitation extremes and underscore the importance of adequately resolving mesoscale frontal features in climate models.