Do Fire Weather Conditions Significantly Affect Wildfires in Subtropical Forests in Taiwan?

Abstract The previous establishment of Taiwan’s Forest Fire Danger Rating Warning System in 2002 relied solely on ground-based fuel aridity considerations, leaving a gap between fire weather information and fire detection. In view of the warming climate and the increasing trend in wildfire frequency, this study analyzes meteorological conditions that promote wildfire occurrence using modern atmospheric reanalysis and satellite data. Correlation coefficient matrix and generalized additive models (GAMs) were constructed to investigate the associations between the interannual variance of wildfire occurrence during regional fire seasons over a 58-yr period (1964–2021) and various fire-related indices, including meteorological conditions, vegetation, soil moisture, and collective indicators represented by the fire weather index (FWI). The study finds that precipitation and humidity, rather than temperature, are the primary climatic drivers of increased wildfire risk in Taiwan. Specifically, prolonged droughts during the summer and fall enhance fuel aridity, deplete groundwater, and deteriorate vegetation, subsequently increasing wildfire probability. Furthermore, a significant inverse relationship between southwestern wildfires and antecedent groundwater 12 months prior suggests that fuel flammability and availability preceding drought events compound the likelihood of widespread wildfires. This study highlights a robust tendency toward increased wildfires in response to drought starting almost a year before, suggesting the feasibility of seasonal prediction application. Significance Statement This study revealed a robust relationship between fire weather conditions and historical wildfire occurrences in Taiwan, the first such finding for its subtropical forests. The importance of considering the drought severity for effective wildfire management was emphasized.