Centre for Environmental Risk Management of Bushfires, University of Wollongong, Wollongong, NSW, Australia.
Association for the Development of Industrial Aerodynamics, Coimbra, Portugal.
PLoS One. 2021 Jan 7;16(1):e0245132. doi: 10.1371/journal.pone.0245132. eCollection 2021.
Spotting is thought to increase wildfire rate of spread (ROS) and in some cases become the main mechanism for spread. The role of spotting in wildfire spread is controlled by many factors including fire intensity, number of and distance between spot fires, weather, fuel characteristics and topography. Through a set of 30 laboratory fire experiments on a 3 m x 4 m fuel bed, subject to air flow, we explored the influence of manually ignited spot fires (0, 1 or 2), the presence or absence of a model hill and their interaction on combined fire ROS (i.e. ROS incorporating main fire and merged spot fires). During experiments conducted on a flat fuel bed, spot fires (whether 1 or 2) had only a small influence on combined ROS. Slowest combined ROS was recorded when a hill was present and no spot fires were ignited, because the fires crept very slowly downslope and downwind of the hill. This was up to, depending on measurement interval, 5 times slower than ROS in the flat fuel bed experiments. However, ignition of 1 or 2 spot fires (with hill present) greatly increased combined ROS to similar levels as those recorded in the flat fuel bed experiments (depending on spread interval). The effect was strongest on the head fire, where spot fires merged directly with the main fire, but significant increases in off-centre ROS were also detected. Our findings suggest that under certain topographic conditions, spot fires can allow a fire to overcome the low spread potential of downslopes. Current models may underestimate wildfire ROS and fire arrival time in hilly terrain if the influence of spot fires on ROS is not incorporated into predictions.
飞火被认为会增加野火的蔓延速度（ROS），在某些情况下成为主要的蔓延机制。飞火在野火蔓延中的作用受到许多因素的控制，包括火强度、火源数量和距离、天气、燃料特性和地形。通过在一个 3 米 x 4 米的燃料床上进行的 30 组实验室火灾实验，我们探索了手动点燃的火源（0、1 或 2）、存在或不存在模型山以及它们之间的相互作用对综合火灾 ROS（即包含主火和合并火源的 ROS）的影响。在平坦燃料床的实验中，火源（无论是 1 个还是 2 个）对综合 ROS 的影响很小。当存在山丘且未点燃火源时，记录到最慢的综合 ROS，因为火灾在山丘下风侧缓慢地向下坡蔓延。这比在平坦燃料床实验中记录的 ROS 慢了多达 5 倍，具体取决于测量间隔。然而，点火 1 或 2 个火源（有山丘）大大增加了综合 ROS，使其达到与在平坦燃料床实验中记录的相似水平（取决于蔓延间隔）。该效应在头部火中最强，火源直接与主火合并，但也检测到中心火蔓延率的显著增加。我们的发现表明，在某些地形条件下，火源可以使火灾克服下坡蔓延的低潜力。如果不将火源对 ROS 的影响纳入预测，当前的模型可能会低估丘陵地形中的野火 ROS 和火灾到达时间。
