PhD Defense of Aurélien COSTES : “Two-way atmosphere-fire coupling for wildfire propagation : modeling, uncertainty and sensitivity “
A wildfire is the result of multi-scale interactions between vegetation, terrain topography and meteorological conditions, which may be enhanced by climate change. Understanding the processes that drive its behavior at the scale of an event is therefore a major issue for ecology and for public safety.
In this thesis work, the Blaze fire model was developed and integrated with the mesoscale atmospheric model Meso-NH in order to reconstruct the detailed chronology of a fire and thus provide a framework to study the interactions between the fire and the micro-meteorology. The response of the coupled Meso-NH/Blaze system to different modelling choices and atmospheric scenarios was studied to quantify the uncertainties associated with the quantities of interest (e.g. the position of the fire front and the latent and sensible heat fluxes along the fire front) and to identify the most influential parameters among those involved in the parameterizations of the propagation speed and heat fluxes. The results showed a significant influence of the atmospheric turbulence on the propagation speed and the fire-induced wind.
In its standard version, the Meso-NH atmospheric model is based on the anelastic hypothesis. The validity of this assumption is questionable in the vicinity of the flaming regions, which are subject to significant heat release. The compressible version of Meso-NH, previously developed for the dry atmosphere, has been extended to the humid atmosphere. A comparison between the anelastic and compressible systems was performed, using the coupled Meso-NH/Blaze model, on the FireFlux I prescribed burning experiment. The results showed that compressible effects become important at very high spatial resolution (10 m) and induce very fine-scale structures such as gravity waves in the fire-induced convection.
François PIMONT – INRAE – Rapporteur
Albert SIMEONI – Worcester Polytechnic Institute University of Maryland – Rapporteur
Arnaud TROUVÉ – University of Maryland -Rapporteur
Jean-Baptiste FILIPPI – CNRS – Examinateur
Céline MARI – CNRS – Examinatrice
Christine LAC – Météo-France – Directrice
Mélanie ROCHOUX – CERFACS – Co-Directrice
Valéry MASSON – Météo-France – Co-Directeur (Invité)