Understanding Shifts in Extreme Precipitation and Synoptic Forces in a Regionalized Framework: The Iberian Peninsula

Extreme precipitation exhibits pronounced local variations associated with dynamic and thermodynamic changes on synoptic and regional scales under global warming inducing important impacts over main socioeconomic sectors such as agriculture, tourism, health and energy. Local-to-regional variations in extreme precipitation are especially marked on climate change hotspots, such as the Iberian Peninsula, reflecting the complex transition between Atlantic and Mediterranean climate influences and further hindering an accurate assessment of climate change impacts and the development of effective adaptation strategies. Therefore, it is crucial to identify variations in atmospheric dynamics as main drivers of changes in the characteristics of extreme precipitation events (EPEs) on subregional scales to better determine the areas subject to specific changes and improve our understanding of extreme weather events to enhance predictability.

In this context, this study conducted a comprehensive analysis using a precipitation regionalization approach with a high resolution (~5 km) gridded dataset for the period 1951-2021 obtaining 8 precipitation-coherent regions in the Iberian Peninsula. EPEs were characterized over each region, and their evolving atmospheric drivers were identified using an objective synoptic classification method with ERA5 data. Besides, an analysis of variations in EPEs intensity and frequency, as well as changes in the associated synoptic conditions and atmospheric water vapor distributions were assessed.

Our results revealed a generalized mean intensification of EPEs for the study period. Nevertheless, we highlight two different pathways: (i) Atlantic regions presenting a moderate (5-10 %) intensification of extreme precipitation linked to an increase of surface flows and counterposing the observed weakening or northward displacement of upper-level perturbations, and (ii) Mediterranean regions showing a marked (15-25 %) extremization of EPEs associated with vorticity intensification at 500 hPa.  Besides, these variations occur alongside an atmospheric moistening (up to 6 mm in the Ebro region) of the moistest air masses denoting the highly complex interplay between thermodynamic and dynamic factors. We emphasize the importance of regionalized approaches to enhance our comprehension on extreme precipitation over regions with complex topography and, more importantly, the corresponding implications on early warning systems and efficient climate adaptation strategies in climate change hotspots.