Jean-Baptiste Filippi

Discrete Event Front-tracking Simulation of a Physical Fire-spread Model

Simulation of moving interfaces such as a fire front usually requires resolution of a large-scale and detailed domain. Such computing involves the use of supercomputers to process the large amount of data and calculations. This limitation is mainly due to the fact that a large scale of space and time is usually split into nodes, cells, or matrices and the solving methods often require small time steps. In this paper we present a novel method that enables the simulation of large-scale/highresolution systems by focusing on the interface and its application to fire-spread simulation. Unlike the conventional explicit and implicit integration schemes, it is based on the discrete-event approach, which describes time advance in terms of increments of physical quantities rather than discrete time stepping. In addition, space is not split into discrete nodes or cells, but we use polygons with real coordinates. The system is described by the behavior of its interface and evolves by computing collision events of this interface in the simulation. As this simulation technique is suitable for a class of models that can explicitly provide the rate of spread, we developed a radiation-based propagation model of wild land fire. Simulations of a real large-scale fire performed by implementation of our method provide very interesting results in less than 30 s with a 3-m resolution with current personal computers.

Representation and evaluation of wildfire propagation simulations

This paper provides a formal mathematical representation of a wildfire simulation, reviews the most common scoring methods using this formalism, and proposes new methods that are explicitly designed to evaluate a forest fire simulation from ignition to extinction. These scoring or agreement methods are tested with synthetic cases in order to expose strengths and weaknesses, and with more complex fire simulations using real observations. An implementation of the methods is provided as well as an overview of the software package. The paper stresses the importance of scores that can evaluate the dynamics of a simulation, as opposed to methods relying on snapshots of the burned surfaces computed by the model. The two new methods, arrival time agreement and shape agreement, take into account the dynamics of the simulation between observation times. Although no scoring method is able to perfectly synthesise a simulation error in a single number, the analysis of the scores obtained on idealised and real simulations provides insights into the advantages of these methods for the evaluation of fire dynamics.

Wildland Fire Behaviour Case Studies and Fuel Models for Landscape-Scale Fire Modeling

This work presents the extension of a physical model for the spreading of surface fire at landscape scale. In previous work, the model was validated at laboratory scale for fire spreading across litters. The model was then modified to consider the structure of actual vegetation and was included in the wildland fire calculation system Forefire that allows converting the two-dimensional model of fire spread to three dimensions, taking into account spatial information. Two wildland fire behavior case studies were elaborated and used as a basis to test the simulator. Both fires were reconstructed, paying attention to the vegetation mapping, fire history, and meteorological data. The local calibration of the simulator required the development of appropriate fuel models for shrubland vegetation (maquis) for use with the model of fire spread. This study showed the capabilities of the simulator during the typical drought season characterizing the Mediterranean climate when most wildfires occur.

Enabling large scale and high definition simulation of natural systems with vector models and JDEVS

This paper describes a new methodology to enable large scale high resolution environmental simulation. Unlike the vast majority of environmental modeling techniques that split the space into cells, the use of a vector space is proposed here. A phenomena is described by its shape, decomposed in several points that can move using a displacement vector. The shape also has a dynamic structure, as each point can instantiate new point because of a change in the space properties or to obtain a better resolution model. Such vector models are generating less overhead because the phenomena is recomputed only if a part of it is entering into a different space entity with different attributes, using cellular space the model would have been recomputed for each neighboring identical cells. This technique uses the DSDEVS formalism to describe discrete event models with dynamic structure, and is implemented in the JDEVS toolkit also presented.

Turbulence and fire-spotting effects into wild-land fire simulators

Abstract This paper presents a mathematical approach to model the effects and the role of phenomena with random nature such as turbulence and fire-spotting into the existing wildfire simulators. The formulation proposes that the propagation of the fire-front is the sum of a drifting component (obtained from an existing wildfire simulator without turbulence and fire-spotting) and a random fluctuating component. The modelling of the random effects is embodied in a probability density function accounting for the fluctuations around the fire perimeter which is given by the drifting component. In past, this formulation has been applied to include these random effects into a wildfire simulator based on an Eulerian moving interface method, namely the Level Set Method (LSM), but in this paper the same formulation is adapted for a wildfire simulator based on a Lagrangian front tracking technique, namely the Discrete Event System Specification (DEVS). The main highlight of the present study is the comparison of the performance of a Lagrangian and an Eulerian moving interface method when applied to wild-land fire propagation. Simple idealised numerical experiments are used to investigate the potential applicability of the proposed formulation to DEVS and to compare its behaviour with respect to the LSM. The results show that DEVS based wildfire propagation model qualitatively improves its performance (e.g., reproducing flank and back fire, increase in fire spread due to pre-heating of the fuel by hot air and firebrands, fire propagation across no fuel zones, secondary fire generation, ...) when random effects are included according to the present formulation. The performance of DEVS and LSM based wildfire models is comparable and the only differences which arise among the two are due to the differences in the geometrical construction of the direction of propagation. Though the results presented here are devoid of any validation exercise and provide only a proof of concept, they show a strong inclination towards an intended operational use. The existing LSM or DEVS based operational simulators like WRF-SFIRE and ForeFire respectively can serve as an ideal basis for the same.