Climate change significantly impacts precipitation at global and regional scale, especially in the Mediterranean region, a climate change hotspot. Existing literature suggests a « water cycle paradox » in this region (decrease of mean precipitation but intensification of heavy precipitations) particularly in the Northern part of the Mediterranean, but this is not yet clear in observations.
This study investigates how the entire precipitation distribution in the Mediterranean has changed over the past and how it might evolve in the future. Using ERA5 reanalysis data (1950-2020) and Euro-CORDEX simulations (1950-2100), the study analyzes temporal trends in precipitation quantiles. We firsy study wet-days (days with more than 1 mm/day) in the past distributions, then look at how changes in dry-day frequency influence the all-days distribution. The study identifies four distinct precipitation regimes: a « U-shape » quantile trend curve (decreasing low to medium quantiles but intensifying extremes), a reversed « U-shape », and two regimes where all quantiles either consistently increase or decrease. Using a Weibull model for the wet-days distribution, the study further determines these four regimes thanks to two parameters. We find regional differences, with a significant intensification in Europe, while in the Mediterranean, changes in precipitation are actually dominated by the increase of dry-days frequency.
Future projections under the RCP5.8 scenario (high emissions) suggest robust trends, with a sharp increase in the frequency of dry-days across the Mediterranean, contrasting with a decline in dry-days and an intensification of wet-days in Northern Europe. The time of emergence of these trends is faster in Northern Europe than in the Mediterranean. This study underlines the essential role of dry-day frequency in the evolution of the precipitation distribution in the Mediterranean.

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Rapportrice : Erika Coppola, Professeure au Centre international de physique théorique (ICTP)
Rapporteur : Paolo Ruti, Professeur à EuMetSat

Examinateur : Jan Polcher, Directeur de recherche CNRS, Laboratoire de Météorologie Dynamique (LMD)
Examinatrice : Juliette Blanchet, Directrice de recherche CNRS, Institut des Géosciences de l’Environnement (IGE)
Examinateur : Mathieu Vrac, Directeur de recherche CNRS, Laboratoire des Sciences du Climat et de l’Environnement (LSCE)
Examinateur : Aurélien Ribes, Chercheur au Centre National de Recherches Météorologiques
(CNRM)

Directeurs de thèse : Philippe Drobinski et Fabio d’Andrea, Directeurs de recherche CNRS, LMD ; et Caroline Muller, Chargée de recherche CNRS, Professeure à Institute of Science and Technology Austria (ISTA).