Effect of canyons on a fire propagating laterally over slopes

Abstract

Forest fires often cause fatal losses, human lives and resources in wildfire-prone regions. Several accidents were registered in canyons with a scenario in which the fire propagates laterally over a slope then enters the canyon causing a rapid increase in the fire’s rate of spread (Viegas, 2004; Lahaye et al. 2018; Pimont et al. 2012). This behaviour is known as eruptive fire behaviour (blow-up) – Viegas et al. 2011 – which usually happens over slopes or in canyon configurations (Viegas, 2005; Viegas, 2006; Viegas and Simeoni, 2011). The behaviour surprised fire management teams in several recorded events and caused loss of lives in some of them. In 2013, at Serra do Caramulo, two firefighters died on a sloped terrain when a flank fire entered a canyon (Viegas et al. 2013). This particular accident motivated us to study the change in the flank fire behaviour over slopes when it enters canyons with the aim of improving the safety of the personnel involved in the combat of wildfires. In this study, we analyse results of laboratory-scale experiments that model a fire spreading latterly over a slope then enters a canyon from its base. We considered various conditions of terrain slope, canyon’s axis angle along with altered canyon configurations. Also, we tested a number of fire approaching angle scenarios. Based on the analysis, we are proposing a mathematical model for predicting the fire’s rate of spread in this configuration along with suggested personnel safety measures under these conditions.