Advancing the BRAMS wildfire–atmosphere modelling system: application to an extreme wildfire event

Abstract

Wildfire smoke significantly perturbs atmospheric composition and radiative balance, with implications for air quality, weather, and climate. Accurately simulating smoke–radiation–convection interactions remains a scientific challenge, particularly at meso- to local scales. This study presents developments in the BRAMS v6.0 modelling system, including the integration of crown fire spread into SFIRE and dynamic coupling of fire-emitted smoke fluxes. These enhancements enable physically consistent simulations of wildfire behaviour, smoke emissions, and their radiative impacts. Fire spread and heat release are used to compute Fire Radiative Power, which drives smoke emissions in real time. These emissions are fully integrated with aerosol–radiation interactions and atmospheric dynamics. The system was applied to the 15 October 2017 wildfire in central Portugal using high-resolution simulations. Model performance was evaluated by comparing a diagnostic Smoke Optical Depth (SOD), computed offline from BRAMS-simulated PM2.5 using a Mie-based framework, with MERRA-2 Aerosol Optical Depth (AOD). Statistical comparison shows that SOD and MERRA-2 AOD share a coherent spatiotemporal structure, with correspondence maximised during the active fire phase. Peak extinction reached ∼ 67 m−1 at 400 nm and absorption approached ∼ 5 m−1 at 550 nm in the near-source plume core, consistent with an OC-dominated scattering regime and localized BC-driven shortwave absorption. The resulting radiative heating contributed to the upward displacement of the CIN layer (≈ 100–200 m) and to the partial erosion of low-level inversions, producing transient stability modifications. Although the model occasionally produces very high near-source PM2.5 and optical-depth values confined to a small number of grid cells, additional diagnostics show that plume-integrated mass and optical properties remain physically consistent and are not dominated by boundary effects. These results demonstrate that the enhanced BRAMS system captures the coupled fire–atmosphere–radiation feedbacks of intense wildfires, improving the interpretation and prediction of smoke-induced thermodynamic and radiative perturbations.