The Spotting Distribution of Wildfires

Abstract

Abstract:In wildfire science, spotting refers to non-local creation of new fires, due to downwind ignition of brands launched from a primary fire. Spotting is often mentioned as being one of the most difficult problems for wildfire management, because of its unpredictable nature. Since spotting is a stochastic process, it makes sense to talk about a probability distribution for spotting, which we call the spotting distribution. Given a location ahead of the fire front, we would like to know how likely is it to observe a spot fire at that location in the next few minutes. The aim of this paper is to introduce a detailed procedure to find the spotting distribution. Most prior modelling has focused on the maximum spotting distance, or on physical subprocesses. We will use mathematical modelling, which is based on detailed physical processes, to derive a spotting distribution. We discuss the use and measurement of this spotting distribution in fire spread, fire management and fire breaching. The appendix of this paper contains a comprehensive review of the relevant underlying physical sub-processes of fire plumes, launching fire brands, wind transport, falling and terminal velocity, combustion during transport, and ignition upon landing.

Defining Extreme Wildfire Events: Difficulties, Challenges, and Impacts

“…The convective activity contributes to changes in the wind speed and wind direction in the immediate vicinity of the fire, caused by the modifications of local winds and creation of inflow into the fire. In addition, it injects steam, smoke, combustion gases and combustion particles into the stratosphere, and launches firebrands into the atmosphere [108], so significantly contributing to extensive spotting. If the amount of energy is enough, the buoyancy of the plume permits its upward convection to the vapor condensation level, with the development of cumuliform cloud tops.…”

“…Spotting refers to the ignition of new fires, due to downwind ignition of brands, firebrands of bark, or larger embers launched from a primary fire [108,118]. It is strongly dependent on the convective column (induced by fire intensity), and on wind velocity and direction.…”

“…Short-range spotting can reach up to several tens of meters, intermediate-range spotting can reach up to a few kilometers, while long-range spotting can reach distances of tens of kilometers ahead of the main fire [119]. Spotting distances of up to 25 km from the primary fire were recorded in 1983 in Australia [108] reaching a maximum recorded distance of 33 km in the 2009 Black Saturday bushfires in Victoria (Australia) [84]. Massive spotting activity increases the ROS and thus the area of intervention, requiring more fire suppression resources.…”

“…Spotting-dominated cases increase the threatened area and potential losses and damages. [108]. Multiple ignitions from spotting can overwhelm firefighting resources [49] and increase the risk of entrapment for both firefighters and residents (learningcenter.firewise.org/Firefighter-Safety/1-11.php).…”

Physical parametrisation of fire-spotting for operational fire spread models: response analysis with a model based on the Level Set Method

“…In an another study, Koo et al (2007) present a physics based multiphase transport model for wildfires (FIRETEC) to study the firebrand transport. In a recent study, Martin and Hillen (2016) also discuss the underlying physical processes for firebrands in detail and they derive a landing distribution based on these physical processes. Besides these statistical approaches, few numerical models based on Large Eddy Simulation (LES) (Himoto and 25 Tanaka, 2005;Thurston et al, 2017;Tohidi and Kaye, 2017) or Computational Fluid Dynamics (CFD) (Wadhwani et al, 2017), small world networks , cellular automata models (Perryman et al, 2013) also exist in the literature.…”