Evaluation of precipitation datasets over Greece. Insights from comparing multiple gridded products with observations

The spatiotemporal precipitation patterns in Greece are influenced by several factors, including the complex topography and the multifaceted climatic regimes of the country. Rain gauges, albeit a reliable tool for the accurate quantification of precipitation, are scarce, sporadic, and not properly maintained. In these instances, gridded datasets may provide a solution by administering spatially and temporally continuous precipitation data. The products, however, reveal limitations in the realistic simulation of precipitation, primarily caused by the intrinsic flaws of the underlying methods used. The assessment of eight of the most spatially and temporally detailed precipitation datasets, namely ERA5-Land (ERA5L), AgERA5, CHELSA-W5E5 v1.1 (CHELSA), MSWEP V2.8, CHIRPS05, IMERG V06 (Final), and E-OBS, compared against field observations acquired from 304 gauging stations across Greece has not been previously attempted. The evaluation is conducted on a daily and a monthly timescale, over a 32-year period (1984–2016), assessing the performance of the gridded products by considering both the country as a whole and its individual regions. The ability of the datasets to correctly portray the occurrence of extreme events and precipitation patterns is examined by statistical metrics and further insights are provided by the application and statistical analysis of climate indices on ground observations. CHELSA, CERRAL and AgERA5 consistently yield acceptable results across statistical metrics, outperforming the other datasets, which exhibit inferior performance in both temporal scales. The statistical analysis reveals distinct patterns of heavier precipitation in northern and western regions, with strong seasonal variability in the West and South and a possible average decennial increase of over 110 mm in mean annual and over 30 mm in extreme precipitation, along the assessment period. Overall, the datasets fail to accurately depict precipitable extremes, but CHELSA and CERRAL stand out as more reliable options for describing the precipitation dynamics in Greece.