Contrasting Trends in Daily Precipitation Extremes and Annual Totals over Southern Europe: Modeling the Role of Mediterranean Sea Surface Warming

Understanding the evolving characteristics of extreme precipitation in the Mediterranean Basin is a critical scientific priority amid ongoing climate change. In particular, the observational analysis reveals an apparent paradox in several areas of this region: while total annual precipitation declines, the frequency and magnitude of concentrated heavy rainfall events do not decline, and in some cases even increase. To elucidate the physical mechanisms underlying this seemingly contradictory behavior, we examine the interplay among marine, atmospheric, and topographic factors, and quantify the contribution of rising sea surface temperatures (SSTs) to the amplification of extreme precipitation events.

The methodological framework is based on the numerical reconstruction of twenty precipitation events that occurred during an active wet season extending from September to December 2019. These events are simulated using the Weather Research and Forecasting (WRF) model, configured at a convection-permitting resolution (2 km as horizontal grid spacing). The simulations are initialized and constrained using ERA5 reanalysis data. To isolate and quantify the specific influence of SST evolution on precipitation dynamics, we implement a PGW (Pseudo Global Warning) approach incorporating three distinct SST scenarios: a baseline configuration utilizing observed 2019 SST values, a retrospective scenario employing SST conditions representative of approximately 1980 (-1 °C), and a prospective scenario incorporating SST increases (+3 °C) consistent with end-of-century projections under various Shared Socioeconomic Pathways (SSPs).

The high-resolution WRF simulations demonstrate robust skill in reproducing atmospheric circulation features and the spatial distribution of precipitation across the complex orographic terrain. Comparative analysis across SST scenarios reveals that elevated SSTs increase the frequency of intense precipitation over terrestrial areas, primarily by increasing atmospheric moisture availability. However, the absolute magnitude of peak rainfall accumulations overland exhibits relatively modest sensitivity to SST variations, as the highest precipitation predominantly occurs offshore.

This investigation underscores the added value of convection-permitting atmospheric modeling approaches in capturing the physical processes governing precipitation extremes in topographically complex Mediterranean coastal environments. The findings contribute substantively to reconciling the apparently paradoxical coexistence of declining annual precipitation totals with intensifying daily precipitation extremes, a pattern with profound implications for water resource management, flood risk assessment, and climate adaptation strategies in vulnerable Mediterranean communities.