Slope effect on junction fire with two non-symmetric fire fronts

Abstract

Background In Pedrógão Grande on 17 June 2017, two fire fronts merged and the propagation of the fire was influenced by the interaction of these non-symmetric fire fronts. Aims This wildfire motivated us to study a junction fire with two non-symmetrical fire fronts. The analysis of the movement of the intersection point and the angle (γ) between the bisector of the fire lines and the maximum rate of spread (ROS) direction is of particular relevance. Methods The study was carried out at Forest Fire Laboratory of the University of Coimbra in Lousã (Portugal) with laboratory experiments. Key results We found that, for small rotation angles (δ), the non-dimensional ROS of the intersection point depends on the slope angle (α) and the initial angle between fire fronts. Conclusions For high α, the non-dimensional ROS was highly influenced by the convection process and γ where the maximum ROS occurred, increased when δ increased. However, the radiation process was more relevant for lower α and influenced the non-dimensional ROS. For these cases, the maximum spread direction was close to that of the fire line bisector. Implications The present work aimed to explain fire behaviour during the Pedrógão Grande wildfire.