Seasonal trends and spatial variability of precipitation extremes in Berlin-Brandenburg, Germany, from 1981 to 2025

Abstract. Precipitation extremes have caused substantial damage in the Berlin-Brandenburg region in recent decades. This study assesses seasonal trends and spatial variability in daily precipitation return levels for 2-, 5-, and 10-year return periods between 1981 and 2025. We use a peaks-over-threshold approach and a non-stationary Generalised Pareto Distribution with a time-dependent scale parameter. The analysis is based on observations from 223 rain-gauge stations operated by the German Meteorological Service (DWD) and the 2 km Central Europe Refined analysis version 2 (CER), a dynamically downscaled product based on the ERA5 atmospheric reanalysis. CER-based return levels show contrasting seasonal patterns: spring return levels decline across nearly the entire domain by up to approximately 20 %, while summer return levels show the largest absolute increases, averaging spatially approximately 5–10 mm d^-1 (+14–15 %), depending on the return period. Summer increases are also spatially more heterogeneous than in other seasons. Autumn return levels increase by up to 19 % across the analysed return periods, whereas winter changes remain weak. The DWD and CER datasets show consistent directions of change, although the CER underestimates the magnitude of summer increases relative to DWD. In some locations, the 2025 2-year summer return level approaches the magnitude of the 5-year return level estimated for 1981, highlighting the relevance of non-stationary return levels for regional risk assessment and future infrastructure planning.