Background Wildfire suppression is becoming more costly and dangerous as the scale and severity of impacts from fires increase under climate change. Aims We aim to identify the key environmental and management variables influencing containment probability for forest fires in Victoria and determine how these change over time. Methods We developed Random Forest models to identify variables driving fire containment within the first 24 h of response. We used a database of ~12 000 incident records collected across Victoria, Australia. Key results Response time, fire size at first attack, number of ground resources deployed (e.g. fire fighters), ignition cause, and environmental factors that influence fire spread (e.g. elevation, humidity, wind, and fuel hazard) were key drivers of suppression success within the first 24 h. However, certainty about the factors influencing suppression reduced as the containment period increased. Conclusions Suppression success hinges on a balance between the environmental factors that drive fire spread and the rapid deployment of sufficient resources to limit fire perimeter growth. Implications Decreasing the period between an ignition and the time of arrival at the fire will allow first responders to begin suppression before the fire size has exceeded their capability to construct a control line.

Merging fires are known as destructive fires resulting in loss of life and houses. Despite growing efforts in the past decade to understand merging fires, there are still many knowledge gaps about their behaviour, especially at the field scale. In this study, we conducted experimental harvested crop burns in Victoria, Australia, in March and April 2021 to better understand thermal behaviour of merging fire fronts. UAVs with visual and thermal cameras were used to capture high-resolution fire propagation and the combustion process of merging fires. During experiments 50 junction fire fronts (32 forward and 18 backward) and 24 coalescence fire fronts were studied. For thermal analysis, 15 forward and 4 backward junction fire fronts, 6 coalescence fire fronts, and 10 parallel fire fronts were considered. Special methods were developed to process IR footages and compare the combustion process of merging fires and linear fire fronts (head and back fires). To do this, regions of interest (ROIs) containing the merging fire and linear fire front were selected in each frame using FLIR Research Studio. The ROIs were then exported using as bitmask images together with radiometric JPEG image containing both fires. Using the R programming platform, we determined the length and shape of the perimeter of fires for each JPEG image and defined buffer zones within the fire perimeter inside the ROI for each fire for further pixel temperature analysis. Thermal analysis showed that for forward junction fires the median temperature of head linear fire fronts was higher than forward junction fires except towards the end of merging. While in backward junction fires, the proportion of pixels with high temperature was much higher than in back linear fire fronts, indicating much larger burning areas. The temperature distributions of coalescence and parallel fires showed a decrease in the number of high-temperature pixels toward the end of the merge for coalescence and throughout for parallel fires. The fire behaviour observed in the field experiments demonstrates the necessity for better understanding of merging of fire fronts and the relationship between fuel, weather and fire line interaction.