Numerical experiments using mesonh/forefire coupled Atmospheric-fire model

International audienceIn this study we attempt to couple the MesoNH atmospheric model in its large eddy simulation configuration with a fire contour model, ForeFire. Coupling is performed at each atmospheric time step, with the fire propagation model inputting the wind fields and outputting heat and vapour fluxes to the atmospheric model. ForeFire model is a Lagrangian front tracking model that runs at a typical front resolution of 1 meter. If the approach is similar to other successful attempts of fire-atmosphere coupled models, the use of MesoNH and ForeFire implied the development of an original coupling method. Fluxes outputted to the atmospheric models are integrated using polygon clipping method between the fire front position and the atmospheric mesh. Another originality of the approach is the fire rate of spread model that integrates wind effect by calculating the flame tilt. This reduced physical model is based on the radiating panel hypothesis. A set of idealized simulation are presented to illustrate the coupled effects between fire and the atmosphere. Preliminary results show that the coupled model is able to reproduce results that are comparable to other existing numerical experiments with a relatively small computational cost (one hour for a typical idealized case on a 200 GFlops capable computer). MesoNH serves as a research model for the meteorological systems in France and Europe, and is well integrated within the operational tool chain. Future validation scenarios will be performed on nested simulations of real large wildfires

Recent dynamics of forest fires in <i>Quercus suber</i> stands in Sardinia, Corsica and Catalonia

In this study, we analyzed the recent dynamics of forest fires in Quercus suber stands in Sardinia (Italy), Corsica (France), and Catalonia (Spain) for the period 2003-2015

ForeFire: open-source code for wildland fire spread models

International audienceFore fire code has been developed to bridge the gap between research and operational code, it is open source, designed for large scale fire simulation, can be easily extended with any new model formulations and can take typical landscape data as input. The code is composed of a simulation engine that has been numerically tested with numerous bindings for different computer languages to be integrated into other scientific environments ranging from SciPy/Numpy to Fortran parallel coupled numerical weather forecast models. This paper presents the general software architecture and concepts, illustrated by examples and use cases in different context

Multi-scale Simulation of a Very Large Fire Incident. Computation From the Combustion to the Atmospheric Meso-scale

International audienceValle male fire devastated more than 3000ha of Mediterranean maquis and pine forest in July 2009. Simulation of combustion processes as well as atmospherics dynamics represents a challenge for such scenarios because of the scale of the phenomenon. A coupled approach between Meso-NH (Non-Hydrostatic) LES (Large Eddy Simulation) meso/microscale scale atmospheric model and ForeFire area simulator is proposed for predicting fine-scale to large-scale phenomenon's involved in such wildfire, showing that using current supercomputers such simulation is possible in a reasonable time. To be representative of the phenomenon, typical resolution required for the simulation of a fire front combustion must be sub-meter (to represent an explicit flame thickness) while atmospheric simulation of a typical domain (several tens of square kilometres) may not be performed at a resolution of finer than 50 meters in a reasonable computational time. The two-way coupling in a Meso-NH/ForeFire simulation typically involve the surface wind to drive the fire, heat (combustion) and water vapour fluxes to be injected in the atmosphere at each atmospheric time step. The ForeFire code has been built so that several front velocity function could be easily defined and applied at different locations of the surface (e.g. a fire front velocity model could be different in forest with canopy than in grassland), likewise surface combustion models can be added and defined in the same way to force the atmospheric model. Meso-NH and ForeFire resolutions are independent and the computational time needed by the surface model is a typically a fraction of the atmospheric simulation. The most active part of the Valle male fire lasted 10 hours, while the computation of the 24 millions grid points took 9 hours on 900 computer cores

Simulation of a Large Wildfire in a Coupled Fire-Atmosphere Model

The Aullene fire devastated more than 3000 ha of Mediterranean maquis and pine forest in July 2009. The simulation of combustion processes, as well as atmospheric dynamics represents a challenge for such scenarios because of the various involved scales, from the scale of the individual flames to the larger regional scale. A coupled approach between the Meso-NH (Meso-scale Non-Hydrostatic) atmospheric model running in LES (Large Eddy Simulation) mode and the ForeFire fire spread model is proposed for predicting fine- to large-scale effects of this extreme wildfire, showing that such simulation is possible in a reasonable time using current supercomputers. The coupling involves the surface wind to drive the fire, while heat from combustion and water vapor fluxes are injected into the atmosphere at each atmospheric time step. To be representative of the phenomenon, a sub-meter resolution was used for the simulation of the fire front, while atmospheric simulations were performed with nested grids from 2400-m to 50-m resolution. Simulations were run with or without feedback from the fire to the atmospheric model, or without coupling from the atmosphere to the fire. In the two-way mode, the burnt area was reproduced with a good degree of realism at the local scale, where an acceleration in the valley wind and over sloping terrain pushed the fire line to locations in accordance with fire passing point observations. At the regional scale, the simulated fire plume compares well with the satellite image. The study explores the strong fire-atmosphere interactions leading to intense convective updrafts extending above the boundary layer, significant downdrafts behind the fire line in the upper plume, and horizontal wind speeds feeding strong inflow into the base of the convective updrafts. The fire-induced dynamics is induced by strong near-surface sensible heat fluxes reaching maximum values of 240 kW m &minus; 2 . The dynamical production of turbulent kinetic energy in the plume fire is larger in magnitude than the buoyancy contribution, partly due to the sheared initial environment, which promotes larger shear generation and to the shear induced by the updraft itself. The turbulence associated with the fire front is characterized by a quasi-isotropic behavior. The most active part of the Aullene fire lasted 10 h, while 9 h of computation time were required for the 24 million grid points on 900 computer cores

Investigation of vegetation fire plumes using paragliders tracks and micro-scale meteorological model

International audienceThis work presents an interesting and unique analysis of an open air fire plume extrapolated from a large amount of paragliders tracks flying over a sugarcane fire during a world cup super final event in february 2013 Columbia. Vertical speeds of over 20 m/s were observed into a narrow core just over the fire. Simulation of the same event shown the relatively good ability of micro-scale meteorological models to represent quantitatively the velocity fields and behavio

High-resolution numerical coupling of wildfire and lava flow simulation with a micro scale atmospheric model

International audienceA coupled approach between Meso-NH (Non-Hydrostatic) LES (Large Eddy Simulation) meso/microscale scale atmospheric model and ForeFire area simulator is proposed for predicting fine-scale properties of surface propagating systems. Originally developed for large wildland fire simulation (with or without atmospheric coupling) ForeFire has been extended for the simulation of lava flow with the same numerical methods. Similarities in both problems include the requirement to take into account high-resolution topography for the simulation of front dynamics and the requirement to use atmospheric sub-mesh models in order to quantify surface energy and species fluxes to the atmosphere. To be representative of the phenomenon, typical resolution required for the simulation of a fire front or a lava flow is sub-meter (to have an explicit flame depth or narrow flow width) while atmospheric simulation of a typical domain (several tens of square kilometres) may not be performed at a resolution of finer than 50 meters in a reasonable computational time. Front tracking is performed by means of Lagrangian markers that allow simulating interface dynamics at high spatial resolution, temporal scheme is event based with a Courant-Friedrichs-Lewy constant time step calculated for each marker iteration, allowing efficient simulation focused on active flow areas. The Lagrangian front dynamics is used to construct a "time of arrival" high-resolution field that is used to perform local budgets of the different surface fluxes models in a way similar to the level-set method. The two way coupling in a Meso-NH/ForeFire simulation typically involve the surface wind to drive the fire or cool the lava surface, and heat and water vapour fluxes to be injected in the atmosphere at each atmospheric time step. The ForeFire code has been built so that several front velocity function could be easily defined and applied at different locations of the surface (e.g. a fire front velocity model could be different in forest with canopy than in grassland), likewise surface fluxes models (combustion, eruption) can be added and defined in the same way, superposed as surface layers with each layer corresponding to an energy, mass or species flux that will be forced in the atmospheric model. Meso-NH and ForeFire resolutions are independent and the computational time needed by the surface model is a typically a fraction of the atmospheric simulation. Parallel strategy for the surface model mimics the one in the atmosphere model (with Lagrangian markers sent between parallel sub-domains), thus recovering the parallel efficiency of the atmospheric optimized parallel design. High-resolution simulation on a large wildfire experiment shows that coupled simulation does compare with the experiment with a better behaviour and more insight (atmospheric flow) than non-coupled simulations. Simulation of the 2007 eruption of Piton de la Fournaise (La Reunion Island, France), as well as the 2009 3000 Ha Aullène fire (Corsica Island, France) show that computations can be performed at large scale in good accordance with observation in a reasonable computational time

Forest fire impact on air quality: the Lançon-De-Provence 2005 case

International audienceForest fires release significant amounts of gases and aerosols into the atmosphere. Depending on meteorological conditions, fire emissions can efficiently spoil air quality and visibility far away from the source. The aim of this study is to evaluate the fire impact on air quality downwind of the burning region in the Mediterranean zone. Wildfire behaviour is simulated using a semi-physical model, ForeFire, based on an analytical resolution of the rate of spread. ForeFire provides the burnt area at high temporal and spatial resolutions; in the mesoscale non-hydrostatic meteorological model Meso-NH fire forcings, as heating and water vapor fluxes, are computed scaling them to the burnt area data given by ForeFire. A chemical scheme is coupled to Meso-NH to account for air quality evolution. Chemical emissions are scaled to the heating fluxes and based on emission factors for the Mediterranean vegetation. The model is used both in a 3D regional and 2D LES configurations. In 2005, an arson forest fire burned nearly 700 ha near Lançon-de-Provence, southeast France. ForeFire was successfully tested on this case study. Here, results from the coupled model, MesoNH-ForeFire, show the sensitivity of atmospheric dynamics and air quality situation to the coupling fire-atmosphere. Simulations put also on evidence how initial conditions and heat fluxes control fire emissions injection height. Finally, tracer distribution is simulated and its pattern shows that although the impact of the fire is visible several kilometres downwind of the burnt area, it remains confined within the planetary boundary layer. This behaviour is confirmed by comparing simulated aerosol particles concentrations with the air quality survey network available in southeastern France

Simulation of coupled fire/atmosphere interaction with the MesoNH-ForeFire models

International audienceFire behaviour is dependent of many physical processes and modelling interaction between all these processes requires a highly detailed and computationally intensive model. In this paper we propose an approach that couples a fire area simulator to a mesoscale weather numerical model in order to simulate local fire/atmosphere interaction. Five idealized simulation cases are analysed showing strong interaction between topography and the fire front induced wind, interactions that could not be simulated in non-coupled simulations. The same approach applied to a real case scenario also shows results that are qualitatively comparable to the observed case. All of these results were obtained in less than a day of calculation on a dual processor computer, leaving room for improvement in grid resolution that is currently limited to fifty meter

Wildfire and the atmosphere: modelling the chemical and dynamic interactions at the regional scale

International audienceForest fires release significant amounts of trace gases and aerosols into the atmosphere. Depending on meteorological conditions, fire emissions can efficiently reduce air quality and visibility, even far away from emission sources. In 2005, an arson forest fire burned nearly 700 ha near Lanc¸on-de-Provence, southeast France. This paper explores the impact of this Mediterranean fire on the atmospheric dynamics and chemistry downwind of the burning region. The fire smoke plume was observed by the MODIS-AQUA instrument several kilometres downwind of the burning area out of the Mediterranean coast. Signatures of the fire plume on air pollutants were measured at surface stations in southeastern France by the air quality network AtmoPACA. Ground-based measurements revealed unusually high concentrations of aerosols and a well marked depletion of ozone concentrations on the day of the fire. The Lanc¸on-de-Provence fire propagation was successfully simulated by the semi-physical fire spread model ForeFire. ForeFire provided the burnt area at high temporal and spatial resolutions. The burnt areas were scaled to compute the fire heat and water vapour fluxes in the three-dimensional meso-scale non-hydrostatic meteorological model MesoNH. The simulated fire plume kept confined in the boundary layer with high values of turbulent kinetic energy. The plume was advected several kilometres downwind of the ignition area by the Mistral winds in accordance with the MODIS and AtmoPACA observations. The vertical plume development was found to be more sensitive to the sensible heat flux than to the fire released moisture. The burnt area information is also used to compute emissions of a fire aerosol-like tracer and gaseous pollutants, using emission factors for Mediterranean vegetation. The coupled model simulated high concentrations of the fire aerosol-like tracer downwind of the burning zone at the right timing compared to ground-based measurements. A chemical reaction mechanism was coupled on-line to the MesoNH model to account for gaseous chemistry evolution in the fire plume. High levels of ozone precursors (NOx, CO) were simulated in the smoke plume which led to the depletion of ozone levels above and downwind of the burning zone. This depletion of ozone was indeed observed at ground-based stations but with a higher impact than simulated. The difference may be explained by the simplified design of the model with no anthropogenic sources and no interaction of the smoke aerosols with the photolysis rates. Ozone production was modelled tens of kilometres downwind of the ignition zone out of the coast