Meteorological drought characterization in Poland by means of the ERA5-Land dataset

Rising drought frequency and severity across Poland and Europe are placing growing pressure on water resources, agriculture, forestry, and hydropower generation. In this context, this study examines meteorological drought conditions in Poland using the Standardized Precipitation Index (SPI), calculated at multiple timescales (3, 6, 12, and 24 months) from the ERA5-Land monthly dataset provided by ECMWF under the framework of Copernicus Climate Change Service Programme. Drought characteristics, including frequency, duration, severity, and intensity, were assessed through run theory applied to SPI values across 4,084 grid points. The findings show that drought occurrences decline significantly as the SPI timescale lengthens, with the 3-month SPI capturing the most events and the 24-month SPI the fewest. In contrast, average drought duration increases with longer timescales, meaning droughts identified over extended accumulation periods tend to last longer. The 24-month SPI, in particular, reflects the highest median duration and variability. A comparable upward trend is observed for drought severity, with longer SPI timescales corresponding to more severe events. Meanwhile, average drought intensity slightly decreases as the timescale increases. When focusing on extreme values, drought frequency remains relatively consistent across timescales, showing only minor median variations. However, maximum drought duration rises clearly with longer SPI periods: short-term SPI captures brief extreme events, while the 24-month SPI identifies prolonged extremes with higher median values and variability. Maximum drought severity follows a similar increasing pattern with longer accumulation periods. Conversely, maximum drought intensity declines as the SPI timescale increases, shorter timescales capture sharper, more intense extremes, whereas longer timescales smooth short-term fluctuations, resulting in less intense but more persistent droughts. Finally, mapping the spatial distribution of drought characteristics across Poland highlights regions that may be particularly vulnerable to future water stress, highlighting the importance of continued drought monitoring and the development of effective adaptation strategies.