Assessing the performance of the CERRA dataset in reproducing extreme weather events in Poland

Understanding the extreme weather events — such as heat waves, heavy precipitation, and episodes of strong winds — is crucial for assessing and managing climate-related impacts on human activities, ecosystems, and the environment. Global reanalysis datasets, including ERA5, and ERA5-Land, are widely used for studying such extremes; however, their relatively coarse spatial resolution can limit their ability to accurately capture localized and high-impact events. The high-resolution Copernicus European Regional ReAnalysis (CERRA) provides a regional alternative that has the potential to improve the representation of extreme meteorological conditions. This study benchmarks the performance of CERRA against established ERA-based reanalyses (ERA5 and ERA5-Land) using in-situ observations from Poland as an independent reference. The evaluation focuses on a set of temperature, precipitation, and wind-related extreme indices to assess how effectively each reanalysis reproduces observed extremes. The results indicate that CERRA outperforms the ERA-based products in representing extreme temperature and precipitation events, while improvements for wind speed extremes are more limited. In addition, three representative case studies — a severe heat wave from July 2010, a heavy rainfall event which led to a flood in June 2010, and a strong wind episode caused by the cyclone Kyrill in 2007 — are examined to provide a process-oriented comparison of CERRA and ERA reanalyses. Overall, the findings demonstrate that CERRA offers clear added value over ERA5 and ERA5-Land for the analysis of extreme weather events in Poland, highlighting its suitability for high-resolution climatological applications.