Weather Regimes and Extreme Precipitation in the Great Alpine Region

This study investigates the relation between Euro-Atlantic large-scale atmospheric circulation and extreme precipitation events (EPEs) in the Great Alpine Region (GAR). We analyze the connection between weather regimes (WRs)—recurrent and quasi-stationary circulation patterns—and EPEs to assess temporal and spatial variations.

The analysis covers the period 1940–2023, using daily geopotential height data at 500 hPa and daily total precipitation data from ERA5 reanalysis. WRs classification mainly follows the methodology outlined by Grams et al. (2017), enabling year-round characterization of atmospheric patterns, which are then linked to average precipitation and EPEs, defined as precipitation exceeding the 95th percentile of the distribution and an intensity greater than 15 mm/day (Q95R15).

Our results show diversities in the average precipitation patterns over the GAR when different regimes occur. In particular, Scandinavian Trough (ScTr), Greenland Blocking (GrBL), Scandinavian Blocking (ScBL) and Atlantic Ridge (AR) seem mostly connected with average precipitation, whose intensity varies according to the season.

Relating WRs and extreme precipitation, we observe that spatially the association between WRs and EPEs varies across GAR sub-regions and depends on the season. We detect higher frequencies of occurrence for ScTr, GrBL, ScBL, AR and Atlantic Trough (ATr) when precipitation above Q95R15 occurs. For instance, during autumn (SON), EPEs are primarily linked to ScTr, ScBL and AR regimes; during winter (DJF) we observe ScTr, GrBL, ScBL, AR and ATr instead. During spring (MAM) and summer (JJA) a clear association is elusive up to now, needing further analysis to be clarified.

Investigations into different sub-periods are ongoing, in order to obtain more insights about how decadal changes due to forced and/or internal variability in the Euro-Atlantic circulation affect the occurrence of EPEs in the GAR.