Investigating the Dynamic Behaviour of Merging Fire Fronts

Publication Date

6-28-2025

Document Type

Article

Publication Title

International Journal of Wildland Fire

Volume

34

Issue

7

DOI

10.1071/WF24126

Abstract

Background: Merging fire fronts have been associated with rapid fire spread and extremely destructive wildfires, yet few studies have characterised these behaviours outside the laboratory. Aims: This study aimed to improve our understanding of merging fire fronts using two experimental harvested crop burns in Victoria, Australia, in 2021. Methods: Unmanned aerial vehicles (UAVs) were used to capture the propagation of fire fronts exhibiting different merging behaviours, including forward and backward (V-shaped) junction fires, linear and coalescing fronts. Key results: A fourfold increase in fire length of forward junction fires led to a doubling of the mean rate of spread (ROS). Forward junction fires spread, on average, three times faster than linear fire fronts, and they also exhibited higher temperature peaks during merging. An increase in the junction angle during merging was observed for all initial junction angles except 60°–90°, but in contrast to laboratory studies, no significant decrease in the ROS was found as the junction angle increased. Conclusions: Our findings suggest that junction fires may lead to other dynamic fire behaviours (DFBs) involving pyroconvective interactions, firebrand showers, fire whirls and other effects. Implications: These results demonstrate the need for further research into merging fire fronts dynamics, to improve operational fire behaviour models.

Funding Number

DP210102540

Funding Sponsor

Bushfire and Natural Hazards Cooperative Research Centre

Keywords

fire behaviour, junction fires, merging fire fronts, rate of spread, spot fire coalescence, temperature, thermal characteristics, wildfires

Department

Meteorology and Climate Science

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