| 04 Nov 2025
Wildfire-atmosphere interactions during the Santa Coloma de Queralt fire: the development of a fire-induced circulation
Abstract. High fireline intensities during extreme wildfire events can trigger pyro-convection, causing unpredictable fire spread behaviour, including faster-than-predicted fire spread and continued burning throughout the night. Earlier studies hypothesised that the main impact of pyro-convection on the fire behaviour is through the acceleration of the rear inflow. To assess this hypothesis, we used MicroHH to create a high-resolution (25 m) turbulence-resolving 3D large-eddy simulation (25.6 by 38.4 km2) of the Santa Coloma de Queralt fire. We validated the in-plume virtual potential temperature using sounding measurements, to our knowledge, a novel approach for validating large-eddy simulations of pyro-convection. In-depth analysis of the wind patterns revealed an increase in rear inflow due to pyro-convection, as well as a frontal inflow of comparable magnitude, as part of a fire-induced circulation ahead of the fire. The frontal inflow could counteract the accelerated rear inflow and is associated with fire-generated vortices and long-range spotting. Additionally, we found that the fire-induced circulation simultaneously deepens and lowers the boundary layer in the 4 km ahead, thereby disrupting the transition from the convective daytime to a stably stratified nighttime boundary layer. This disruption provides a plausible explanation for the sustained nighttime burning during the Santa Coloma de Queralt fire. Therefore, we argue that the primary impact of pyro-convection on wildfire behaviour depends on the balance between wind patterns at the rear and in front of the fire (revised hypothesis), rather than solely on the acceleration of the rear inflow (original hypothesis).
This manuscript presents a Large-Eddy Simulation (LES) study of the 2021 Santa Coloma de Queralt (SCQ) fire using MicroHH, with the novel inclusion of in-plume radiosonde data for validation. The objective is to examine how pyro-convection modifies near-fire wind patterns and boundary-layer structure, but also the evaluation of Micro-HH and using radio soundings.
The topic is scientifically significant, addressing the mechanisms behind sustained nighttime burning and extreme fire behaviour. The work demonstrates good numerical design and physical interpretation; in particular, the use of radiosonde profiles to validate the plume structure is original and valuable for the field, asn well as comparing it to NWP.
Scientific relevance can therfore be high. The study advances quantitative understanding of fire-induced circulations and provides evidence that frontal inflow, rather than rear-inflow enhancement alone, may governs plume–atmosphere coupling. The use of an LES code not originally developed for wildfire problems shows capability and will interest both fire and boundary-layer communities.
Major remarks:
Scope of “validation”. The paper repeatedly refers to validation, but it is not fully clear what is validated—MicroHH as a model, the fire setup, or the specific thermodynamic representation. Maybe just a "Comparison"or investigation. A clearer statement that this is a comparative test against a single radiosonde, not a formal model validation, would help.
Fire representation. The fire seems to be implemented as a dynamic heat-flux patch maybe with explicit combustion or spread, but it seems very vague or unclear in the current redaction, do you have any isochrones, fuel maps, orography, it appears not, as well as boundary condition, it is perfectly OK, but if it is a somehow idealized fire it should be clearly presented as such. Also this simplification should be justified earlier and clearly separated from coupled fire-atmosphere modelling claims. And if you have, it would be useful to provide basic the actual parameters of the assumed fuel type and flux intensity and to state whether topography was flat or taken from ERA5.
Boundary conditions. ERA5 forcing and the periodic lateral boundaries may influence inversion height and plume recirculation. A short sensitivity test or discussion (possibly moved from the Appendix) should quantify the expected impact.
Physical metrics. Beyond potential temperature, additional diagnostics (e.g., CAPE, wind profile, potential temperature) could strengthen the interpretation of the radiosonde comparison and the discussion of plume dynamics.
Figures. Some figures (e.g., Fig. 3–5) would benefit from clearer units and labels—particularly for “normalised flux”, velocities (m s⁻¹), and altitude scales.
Minor issues
– Define clearly “frontal inflow” and “rear inflow” on first use.
– Clarify whether “ERA5” or “ERA-5” is used consistently.
– Proofread for minor grammatical errors and duplicated references.
Overall the manuscript is scientifically sound and offers a significant contribution to the understanding of wildfire-atmosphere coupling. It would merit full review and likely publication after major revisions aimed at clarifying the methodological scope (validation vs. comparison), documenting the fire setup, and tightening figure presentation. Given these strengths and the importance of the dataset, I recommend accepting it for external review