Coupled Fire-Atmosphere modelling: Some Findings and current challenges based on Portuguese case studies

Abstract

High-resolution atmospheric models and their coupling with fire propagation models are powerful tools for better understanding the behaviour of rural fires and their effects on the atmosphere. Portugal is one of the European countries with most burned area and numerous ignitions. In 2017, Portugal was affected by several megafires with burned areas larger than 10 000 hectares, some of which led to the formation of convective clouds: pyro-cumulus (pyroCu) and pyro-cumulonimbus (pyroCb). These phenomena can significantly influence the evolution of fire fronts by altering surface winds and raising spread rates, creating extra difficulties for firefighting and increasing burned areas. These rural fires of 2017 were the starting point for studying the atmospheric environment that favours ignitions and fire spread and the effects of fires on the atmosphere, particularly the generation of pyroconvection. In this study, Pedrogão Grande (June 17) and the Quiaios (October 15) mega-fires are chosen as case studies for numerical simulations with the MesoNH atmospheric model coupled with the ForeFire fire propagation model. The simulations show the development of pyroCu and pyroCb clouds produced by intense convective updrafts due the heat fluxes generated generated during combustion. The simulations have improved our understanding of the evolution of the fire environment and the role played by downbursts originating from pyroCb clouds and provided insights about numerical modelling of pyroconvective clouds using Meso-NH/ForeFire simulations. Finally, we use the results obtained in this work to illustrate the current state-of-the art of coupled fire-atmosphere modelling, its limitations and challenges.