Thermodynamic and Dynamic Contribution in Precipitation Extremes over Europe and theMediterranean Basin.

Extreme weather events such as heavy precipitation and droughts are key indicators of climate
change, yet their variability and underlying drivers remain challenging to assess. This study
investigates trends in extreme precipitation over Europe and the Mediterranean from 1981 to 2022
using CHAPTER (Computational Hydrometeorology with Advanced Performance to Enhanced
Realism), a high-resolution (3 km × 3 km). CHAPTER is a convection-permitting dynamical
downscaling of the ERA5 global reanalysis, performed with the WRF numerical model. The high
spatial resolution of CHAPTER enables a detailed analysis of convective processes that global
climate models cannot directly represent. A robust physical scaling diagnostic is applied to
decompose changes in hourly extreme precipitation into thermodynamic and dynamic contributions.
Results indicate an overall increase in extreme precipitation intensity of 2.5% per degree of
warming, with significant regional variations. The strongest increases are observed over the eastern
Mediterranean, particularly in the Ionian Sea, while slight decreases appear over the Iberian
Peninsula and the western French coasts. These spatial patterns strongly correlate with
thermodynamic scaling, suggesting that precipitation changes at a regional scale are primarily
driven by increasing atmospheric moisture content, consistent with global-scale findings. More
specifically, these spatial trends in extreme precipitation closely align with surface changes in
specific humidity.
Conversely, the dynamic contribution exhibits significant spatial variability, suggesting a strong
influence of natural variability over the 42-year period studied. A statistical significance test
confirms that most observed trends in extreme precipitation are not robust at a 95% confidence
level, reinforcing the hypothesis that natural variability plays a dominant role.