Long‐Term Variability of the Fire Weather Index in Poland and Associated Meteorological and Atmospheric Circulation Conditions (1951–2025)

This study assesses the spatial and temporal variability of fire‐weather conditions in Poland during the warm season from April to September over 1951–2025 using the Fire Weather Index (FWI) derived from ERA5‐Land reanalysis data. Validation against observations from 29 stations of the Institute of Meteorology and Water Management–National Research Institute (IMGW‐PIB) showed strong correlations for daily FWI and percentile‐based interannual variability. The analysis focuses on long‐term FWI changes, interannual covariability with its meteorological inputs, and atmospheric circulation patterns associated with high‐FWI episodes. The increase in warm‐season FWI was strongly spring‐dominated. April–May FWI increased significantly across virtually all of Poland, whereas July–August, despite having the highest mean FWI, showed a weaker positive trend whose spatial significance was limited to about one‐quarter of the country. Despite the observed long‐term increase in fire‐weather potential, annual burned area did not show a corresponding increase during 1990–2025. Mean FWI values were highest mainly in western and central Poland, whereas lower values occurred in the southern mountains and, in some months, along the Baltic coast. Extreme fire‐weather days, defined as FWI above the local 95th percentile, were characterized primarily by lower relative humidity, higher air temperature, and precipitation deficits, while wind‐speed anomalies were smaller. Analyses of atmospheric circulation fields and circulation types indicated that high‐FWI episodes were accompanied by anticyclonic conditions over Central Europe. Backward‐trajectory clustering provided a descriptive summary of broad transport pathways, although separation among several clusters was weak. Overall, the results indicate a long‐term intensification of meteorological fire‐weather conditions in Poland over 1951–2025, concentrated mainly in spring.