Analysing the bimodal distribution of annual forest fires in Croatia: Implications for firefighting operations planning

This paper examines annual trends in forest fire events and forest fire hazard indices in Croatia. The primary data source is the European Forest Fire Information System (EFFIS), which provides average weekly data on forest fire events and indices. The analysis in this study focuses on the annual distribution of the number of forest fires, revealing a distinct bimodal pattern. Interestingly, this bimodal distribution of fire events is not reflected in the corresponding annual distribution of the severity index, which suggests different factors impacting the number and intensity of fires throughout the year. Using machine learning techniques, including dendrogram analysis and k−means clustering, the study identified two statistically significant clusters in the data. The first cluster corresponds to a spike in the number of fire events in March. However, this increase in fire frequency is not accompanied by a corresponding rise in the severity index, suggesting that the fires are predominantly caused by human activities, such as agricultural burning, debris burning, or other forms of negligence, rather than by natural causes. The second cluster, characterized by a significant increase in the number of fires from mid−June to the end of September, coincides with the peak in the annual distribution of the severity index. This pattern suggests that fires occurring in this period are primarily driven by natural causes, such as prolonged droughts, high temperatures, and strong winds typical of the Mediterranean summer climate. Between these two clusters lies a relatively calm phase from April to early June. The phase can serve as a strategic operational pause, allowing fire management agencies to regroup and prepare for the critical fire season in the summer months. By understanding the temporal distribution and underlying causes of forest fires in Croatia, this study provides valuable insights and can help to devise more effective fire prevention and response strategies, ultimately contributing to the protection of the country’s valuable forest resources.