Detection and characterization of precipitation extremes and geohydrological hazards over a transboundary Alpine area based on different methods and climate datasets

Abstract. Extreme hydrometeorological events are increasingly raising concern in central Europe, particularly in the European Alps, where they pose significant threats to ecological and socio-economic systems. To support authorities to improve risk reduction and climate change adaptation efforts it is crucial to understand upon which conditions the available meteorological data allow for the detection of meteorological extremes able to trigger hazardous events in a given area of interest. Considering precipitation as a key triggering factor for such hazards, this study explores different approaches for the identification of extreme precipitation events and the assessment of their link to geohydrological processes (i.e., landslides, debris flows, floods) observed in a transboundary Alpine region between Austria and Italy from 2003 to 2020. Three definitions of extremes based on regional and local-scale statistics were applied to the daily precipitation grids from four meteorological datasets and the events identified by each combination of datasets and statistical approaches were then compared with hazard occurrences both spatially and temporally. Results show that daily precipitation fields identified as extreme by local-scale statistics, i.e., considering local intensities, report a greater spatial and temporal match with observed hazards. High-resolution observation products, especially if in situ observations are combined with radar data, offer a more detailed and reliable representation of precipitation intensities and relation with hazards. For all methods, the coarser-resolution reanalysis ERA5-Land shows the lowest performance in explaining hazard occurrences, mostly due to the gap between the spatial scale resolved by the data and the one relevant for geohydrological processes. The precipitation statistics and the fields of extreme events identified for the considered region are provided as a reference for further studies. The outcomes of this work can provide methodological recommendations for supporting the understanding and modelling of transboundary risks related to precipitation extremes triggering geohydrological processes in the Alpine regions.