Meteorological conditions during mega-fires and pyro-convection in Portugal in October 2017

Abstract

A wildfire has multiple variables that influence its development, such as topography, type and amount of fuels and meteorological factors. In this study, the goal is to better understand the meteorological conditions associated with the mega-fires occurred in Portugal on October 15, 2017. For that purpose, the MesoNH atmospheric model was used. The model can represent the atmospheric motions in different scales and was configured in different resolutions aiming to investigate the events in different temporal and spatial scales [1]. A large domain (4500 km × 3750 km) was designed for studying synoptic conditions with a horizontal resolution of 15 km. Small scale aspects were investigated using the MesoNH coupled with a fire propagation model (ForeFire) [2]. The numerical experiment was configured with three nested domains with horizontal resolution of 2000m, 400m, and 80m and 300 vs 300 grid points each one. The Quiaios wildfire was chosen as the case study. The results highlight the importance of the use of cloud resolving models with very-high spatial and temporal resolutions for representing the development of the pyro-convective phenomena. The coupled simulation showed the development of Pyro-Cumulus clouds in the fire plume. In the largescale context, the simulation well represented the evolution of the hurricane Ophelia during its life cycle and the moment that it approached to Portugal, indicating the important role played by the weather system inducing strong south-westerly winds over Portugal in the late afternoon of 15 October. Therefore, the passage of the hurricane Ophelia along the Portuguese coast brought strong winds that helped in the rapid spread of the fires, large burned areas, and pyro-clouds development.