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

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## Abstract

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## 1. Introduction

## 2. Presentation of the Models and Coupling Methods

#### 2.1. Meso-NH Atmospheric Model

#### 2.2. Wildfire Propagation

#### 2.3. Fire Velocity (ROS) Model

#### 2.4. Coupling Atmospheric and Wildfire Models

## 3. Presentation of the Simulation

#### 3.1. Observations of the Fire Case

#### 3.2. Numerical Configuration

#### 3.3. Data Sources

^{®}for road and drainage networks. The Digital Elevation Model (DEM) is extracted from IGN BD ALTI

^{®}25-m resolution. IFN classes have been grouped according to the methodology developed in [43] and use the proposed characterization of the vegetation. Figure 4 presents the fuel distribution over the final burnt area, with four main classes, as well as small non-burnable area providing fuel breaks. Vegetation heterogeneity, orography or small unreported older fires influence the fire propagation at small scales. These heterogeneities are not accounted for in this work, and the chosen fuel types are taken as the best guesses.

## 4. Simulation Results

#### 4.1. Qualitative Results of the “Coupled” Simulation

#### 4.2. Dynamical Plume Structure

#### 4.3. Computational Time

## 5. Conclusions

## Supplementary Materials

## Author Contributions

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Sartene weather station records on 23 July 2009 (in hours UTC): temporal evolution of 10-m wind speed (in red, in $\mathrm{m}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-1}$), 2-m temperature (in blue, in deg C) and relative humidity (in black, in %).

**Figure 3.**Aullene’s fire, markers (blue) and heat fluxes above 30 $\mathrm{kW}\phantom{\rule{0.166667em}{0ex}}{\mathrm{m}}^{-2}$ at fire resolution (5 m) (

**A**) used to force the atmospheric surface fields (resolution 50 m) (

**B**).

**Figure 4.**Overview of the fuel distributions with the four main fuel classes over the final observed fire area over elevation in gray shades.

**Figure 5.**View of the “coupled” fire simulation (grey scale) 27 min, 1 h, 2 h and 3 h 30 after the beginning of the fire, with corresponding observed fire passing points (yellow marks), superimposed on the real burnt area including fire fighting actions (dashed red area). The horizontal extension at the base of the figure is 5 km.

**Figure 6.**Simulated smoke tracer on 23 July 2009 (

**a**) in the 50-m resolution domain compared to the plume’s photograph (at the top left) at 14:50 UTC and (

**b**) in the 600-m resolution domain highlighted in red (A) at 15:00 UTC compared to the MODIS image (B) of Corsica at 14:50 UTC.

**Figure 7.**Vertical cross-section of the wind speed (in $\mathrm{m}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-1}$, between blue and red) and streamlines initiated at the ground and colored according to the vorticity (in $\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-1}$, between green and pink) at 1500 UTC.

**Figure 8.**Horizontal cross-sections on 23 July 2009 at 1500 UTC: (

**a**) envelop of the fire front (in black) at the ground superimposed on the 10-m wind vectors (arrows) of the “coupled” simulation and on the orography (color, in m) with the axis of the vertical cross-sections; (

**b**,

**c**) 10-m wind speed (in $\mathrm{m}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-1}$) with wind vectors superimposed for the (

**b**) “uncoupled” and (

**c**) difference “coupled minus uncoupled” simulations; (

**d**) Vertical velocity at a 300-m height (in $\mathrm{m}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-1}$) for the difference “coupled minus uncoupled” simulations. Orography isocontours are superimposed in (

**b**).

**Figure 9.**Vertical cross-sections on 23 July 2009 at 1500 UTC: (

**a**,

**b**) horizontal wind (in $\mathrm{m}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-1}$) with wind vectors superimposed for (

**a**) the “uncoupled” simulation and (

**b**) the “coupled” one along the direction of propagation (axis (A) in Figure 8a); (

**c**,

**d**) vertical velocity difference between “coupled” and “uncoupled” simulations (in $\mathrm{m}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-1}$) with the wind vectors (arrows) (

**c**) across the fire front (axis (B)) and (

**d**) along the direction of propagation (axis (A)).

**Figure 10.**Horizontal cross-sections on 23 July 2009 at 1500 UTC: 2-m temperature (in deg Celsius) for the (

**a**) “uncoupled”; (

**b**) “coupled” and (

**c**) the difference “coupled minus uncoupled”; (

**d**) Sensible heat flux at a 20-m height for the difference “coupled minus uncoupled” (in $\mathrm{kW}\phantom{\rule{0.166667em}{0ex}}{\mathrm{m}}^{-2}$). Isolines of orography are superimposed in (

**a**).

**Figure 11.**Difference between “coupled” and “uncoupled” simulations on 23 July 2009 at 1500 UTC: Horizontal cross-sections of (

**a**) 10-m horizontal divergence (in ${\mathrm{s}}^{-1}$) with the fire tracer superimposed (in black); (

**b**) 10-m pressure (in Pa).

**Figure 12.**Vertical cross-sections along the direction of propagation (axis(A) in Figure 8a) on 23 July 2009 at 1500 UTC of Turbulent Kinetic Energy (TKE) (in ${\mathrm{m}}^{2}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-2}$) for the (

**a**) “uncoupled” and (

**b**) the difference “coupled minus uncoupled” (with a ratio of 10 between isocontours); (

**c**) dynamical production of TKE (in ${\mathrm{m}}^{2}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-3}$) and (

**d**) thermal production of TKE (in ${\mathrm{m}}^{2}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-3}$) for the difference “coupled minus uncoupled”.

**Figure 13.**Mean kinetic energy spectra for vertical wind on 23 July 2009 at 1500 UTC for the “Coupled” (continuous line) and “Uncoupled” (dashed line) simulations according to the wavelength (in m). The dashed line indicates the power law with an exponent of $-5/3$ (the Kolmogorov spectrum).

**Figure 14.**“Coupled” simulation on 23 July 2009 at 1500 UTC: vertical cross-sections along the direction of propagation (axis in Figure 8a) of (

**a**) zonal wind variance ${u}^{\prime 2}$, (

**b**) meridional wind variance ${v}^{\prime 2}$ and (

**c**) vertical wind variance ${w}^{\prime 2}$ (in ${\mathrm{m}}^{2}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-2}$).

**Figure 15.**“Fire-to-atm” simulation on 23 July 2009 at 1500 UTC: horizontal cross-sections of (

**a**) the fire front (in black) at the ground superimposed on the wind vectors (arrows) and on the orography (color, in m); (

**b**) the difference between “fire-to-atm” and “uncoupled” simulations of 10-m wind intensity with wind vectors superimposed (in $\mathrm{m}\phantom{\rule{0.166667em}{0ex}}{\mathrm{s}}^{-1}$).

Shrubs | Pine | Mixed | Maquis | |
---|---|---|---|---|

$\sigma $ (kg·m${}^{-2}$) | 0.6 | 2 | 1.5 | 0.8 |

E (m) | 0.5 | 3 | 2.5 | 2 |

m (%) | 8 | 15 | 10 | 8 |

$\Delta h$ (MJ·kg${}^{-1}$) | 18.6 | 16 | 17 | 18.6 |

Exec. Time | Ratio | Overhead | |
---|---|---|---|

(for 6000 s) | (/Real Time) | (%) | |

Uncoupled | 7550 | 1.26 | 0.00 |

Fire-to-atm | 8700 | 1.45 | 15.23 |

Coupled | 8240 | 1.37 | 9.14 |

Coupled | 4580 | 0.76 | 9.14 |

(depopulated) |

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## Share and Cite

**MDPI and ACS Style**

Filippi, J.-B.; Bosseur, F.; Mari, C.; Lac, C.
Simulation of a Large Wildfire in a Coupled Fire-Atmosphere Model. *Atmosphere* **2018**, *9*, 218.
https://doi.org/10.3390/atmos9060218

**AMA Style**

Filippi J-B, Bosseur F, Mari C, Lac C.
Simulation of a Large Wildfire in a Coupled Fire-Atmosphere Model. *Atmosphere*. 2018; 9(6):218.
https://doi.org/10.3390/atmos9060218

**Chicago/Turabian Style**

Filippi, Jean-Baptiste, Frédéric Bosseur, Céline Mari, and Christine Lac.
2018. "Simulation of a Large Wildfire in a Coupled Fire-Atmosphere Model" *Atmosphere* 9, no. 6: 218.
https://doi.org/10.3390/atmos9060218