Use of atmospheric modelling to assess fire danger in mainland Portugal during heatwave periods

Abstract

Intense heatwave periods increase the likelihood of extreme wildfires which can lead to negative impacts on many socio-economic sectors. Also, there is still a need to better understand how this phenomenon can impact specific regions in terms of fire danger. The present study aims to investigate three heatwave periods occurring in 2003, 2018 and 2019. All the periods were associated with significant wildfires, two of them linked to mega fires in southern Portugal. The MesoNH is a full-physics non-hydrostatic limited-area research model able to represent atmospheric motions in different scales and has been used to explore the structure and dynamics of the atmosphere during the events. The model was configured with 2.5 km grid spacing and performed for several days depending on the episode. All the experiments were designed with 50 vertical sigma levels unequally spaced, stretching gradually from 30 m (bottom) to 900 m (top). Initial and lateral boundary conditions were provided by European Centre for Medium-Range Weather Forecasts (ECMWF) analysis, with updates every 6 h. The Monchique wildfires in August 2003 and 2018 burned above 25,000 ha. In 2019, the Vila de Rei wildfire burned almost 10,000 ha. All these wildfires’ events occurred under a heatwave influence. The numerical experiment allowed identifying some areas with potential to be affected by wildfires, mainly the regions where orographic effects act to enhance the fire danger. The atmospheric conditions simulated helped to explain the intense fire activity for several days. The heatwave environment associated with extreme heat, very low humidity, and airflow interacting with the local topography favoured the behaviour and evolution of the fires. In this study, the findings show the benefits of the use of cloud-resolving models over large domains to assess the fire danger conditions and helped us to better understand the atmospheric dynamic influencing the development of wildfires. Furthermore, the results may help define firefighting strategies in specific areas, namely in Southern Portugal. 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).