Understanding Extreme Weather in a Warming European-Mediterranean Region: From Localized Convection to Organized Cyclones

Extreme precipitation and high-impact cyclones represent some of the most damaging manifestations of climate variability within the European–Mediterranean region. While driven by global thermodynamic trends, the impacts of these events are governed by atmospheric processes spanning a broad range of spatial and temporal scales. This thesis investigates convective extremes by integrating high-resolution, convection-permitting regional climate modeling with large-scale reanalysis diagnostics. This dual approach characterizes both local precipitation dynamics and the synoptic environments conducive to intense Mediterranean cyclones. The first part of this thesis evaluates extreme precipitation and its sensitivity to recent warming using a newly developed dataset: "Computational Hydrometeorology with Advanced Performance to Enhanced Realism" (CHAPTER). CHAPTER provides a high-resolution (3 km) dynamical downscaling of the ERA5 reanalysis over Europe and the Mediterranean basin, using the Weather Research and Forecasting (WRF) model. The added value of this dataset is rigorously validated against daily precipitation and near-surface temperature observations. This evaluation demonstrates that CHAPTER accurately reproduces observed climatological patterns and extremes, establishing a physically consistent foundation for investigating long-term trends. Analysis of the simulation reveals a marked increase in precipitation extremes over recent decades. To interpret these shifts, a diagnostic framework was used to decompose trends into thermodynamic and dynamic contributions. On one hand, thermodynamic effects, directly driven by increased atmospheric moisture at warmer temperatures, produce a broadly positive and uniform signal. On the other hand, changes in convective dynamics, primarily linked to vertical motion, emerge as the primary driver of regional intensity and structure. Furthermore, the results highlight a critical coupling between land–atmosphere interactions and convective intensity mediated by surface moisture availability. In regions where soil moisture and marine moisture supply remain abundant, enhanced evaporation supports deeper convection, leading to increases in both mean seasonal precipitation and hourly extremes. Conversely, declining soil moisture levels limit surface evaporation, which is associated with a reduction in extreme hourly rainfall intensity. The second part of the thesis examines Mediterranean cyclones, with particular emphasis on systems that develop a deep warm core. By comparing the large-scale environments of classical baroclinic cyclones, intense cold-core systems, and disturbances with a deep warm core, the analysis identifies the key factors favoring the development of tropical-like characteristics. These include substantially higher potential intensity and weaker vertical wind shear. Enhanced potential intensity arises from the combined effect of elevated sea surface temperatures and strong upper-level intrusions that destabilize the atmospheric column. Overall, this thesis builds on the central role of atmospheric dynamics in both convective processes and cyclone evolution to control extreme weather in the Euro-Mediterranean region. The present work underscores the importance of high-resolution modeling for understanding and anticipating climate-driven changes in extremes.