  The Mediterranean is strongly affected by Extreme Precipitation Events
(EPEs), sometimes leading to negative impacts on society, economy, and the
environment. Understanding such natural hazards and their drivers is essential
to mitigate related risks. Here, EPEs over the Mediterranean between 1979 and
2019 are analyzed, using ERA5 dataset from ECMWF. EPEs are determined based on
the 99th percentile of the daily distribution (P99). The different EPE
characteristics are assessed, based on seasonality and spatiotemporal
dependencies. To better understand the connection to large-scale atmospheric
flow patterns, Empirical Orthogonal Function (EOF) analysis and subsequent
K-means clustering are used to quantify the importance of weather regimes to
EPE frequency. The analysis is performed for three different variables,
depicting atmospheric variability in the lower and middle troposphere: Sea
level pressure (SLP), temperature at 850 hPa (T850), and geopotential height at
500 hPa (Z500). Results show a clear spatial division in EPEs occurrence, with
winter (autumn) being the season of highest EPEs frequency for the eastern
(western) Mediterranean. There is a high degree of temporal dependencies with
20% of the EPEs (median value of all studied grid-cells), occurring up to 1
week after a preceding P99 event at the same location. Local orography is a key
modulator of the spatiotemporal connections and substantially enhances the
probability of co-occurrence of EPEs even for distant locations. The clustering
clearly demonstrates the prevalence of distinct synoptic-scale atmospheric
conditions during the occurrence of EPEs for different locations within the
region. Results indicate that clustering based on a combination of SLP and Z500
can increase the conditional probability of EPEs by more than three (3) times
(median value for all grid cells) from the nominal probability of 1% for the
P99 EPEs.
