Exploratory analysis of short-duration rainfall extremes from sub-hourly observations in Northern Europe

Study Region: Sub-hourly rainfall records from 2438 rain gauges in Denmark, Germany, Norway, Poland, and Sweden. 
Study Focus: Intensity-Duration-Frequency (IDF) curves are commonly used for deriving design rainfall events, but estimation methods and accessibility vary across countries. This study explores whether harmonised sub-hourly rainfall observations from multiple countries can be analysed using one uniform baseline framework, and what this analysis reveals about the consistency and spatial structure of transnational IDF estimates. Using Annual Maximum Series (AMS) for durations of 15 min to 12 h, the Generalised Extreme Value (GEV) distribution, and L-moment estimation, we estimated GEV parameters and 10-year return levels and assessed internal and external consistency. 
New Hydrological Insights for the Region: L-moment ratio diagrams and goodness-of-fit tests support the GEV distribution across the study area. While location and scale parameters exhibit large-scale spatial patterns with a latitudinal gradient, shape parameters are spatially heterogeneous. Return levels estimated using our uniform method show moderate to strong agreement with national reference datasets, with mean relative errors from −32 to 15.1% across countries, and most national estimates falling within the bootstrap 95% confidence intervals of our estimates. Discrepancies are largest in Poland and Germany, reflecting differences in record length, temporal resolution, and methodology. The results show that harmonised sub-hourly rainfall records can support consistent transnational IDF estimation and provide a basis for an open-access transnational IDF dataset.