Wildfire activity and related weather patterns in Ukraine

Abstract Wildfires are an important part and natural process of most terrestrial ecosystems. Fire weather is one of the most important factors influencing fire activity and is largely determined by regional atmospheric circulation. An analysis covering the period from 2001 to 2021 showed that in Ukraine, fire activity follows a clear seasonal pattern, peaking in August and an additional peak in early spring. The largest burned areas are concentrated in the southern steppe regions of Ukraine, while the highest hot spots number is recorded in the northern half of the country, in the forest-steppe and mixed forests. The application of the Jenkinson–Collison classification to classify synoptic processes over Ukraine showed that the most frequent circulation types were associated with westerly advection, accounting for a total of 35%. Westerly flows dominated throughout the year; about 40% of circulation types with advection from the north and northeast occurred in summer, while more than 30% of southerly flows were observed in winter. One-third of all anticyclones occurred in autumn, and a similar proportion of cyclones was recorded in spring. No significant trends were found in either fire activity or the frequency of circulation types during the study period. The analysis of relationship between circulation types and fire activity showed that about 50% of annual fire occurrences (hotspots number) are associated with three circulation types, two of which are linked to advection from the west and east. The third significant contributor to fire occurrence is relatively rare anticyclones, while in different seasons the contribution of other circulation types may also increase. Analysis of two selected periods of high fire activity, in 2008 and 2020, revealed significant positive anomalies in the frequency of circulation types associated with the highest number of hotspots.