Application of atmospheric modelling to understand wildfires environment in Southern Portugal

Abstract

Meteorological conditions are an important factor contributing to extreme fire environment. Southern Portugal has some susceptible regions to fire with at least 4 mega fires occurring in the last two decades. Aiming to investigate in detail the atmospheric environment of large fires, several numerical simulations were performed using the Meso-NH non-hydrostatic research model. Some simulations were configured using a simple domain with a horizontal resolution of 2.5 km, while others were performed using a grid nesting technique with an inner domain of 500 m resolution. The vertical grid was configured with 50 stretched levels following the terrain. Initial and boundary conditions were provided by the ECMWF analyses and updated every 6 h. The simulations have shown the important role played by regional orography in creating favourable fire weather conditions. For instance, the interaction of the airflow with orographic effects created conditions for the rapid spread of the fire fronts in some cases, namely downward motions on the leeward side of the mountains. These effects were associated with strong wind gusts and turbulent motion at surface. Moreover, the numerical simulations indicated air temperatures near the surface above 30⁰C, and relative humidity below 30% influencing the fine fuel availability in the mega-fire cases. The study highlighted the advantages of using atmospheric modelling to better understand the significant wildfires in Southern Portugal, especially in a region marked by its fire susceptibility and vulnerability. This study was funded by national funds through FCT-Foundation for Science and Technology, I.P. under the PyroC.pt project (Ref. PCIF/MPG/0175/2019).