Effect of Spatiotemporally Varying Fuel Moisture Content on Turbulence Statistics During Fire Propagation

Abstract

Prescribed burns are valuable tools utilized for land management. They serve the purpose of reducing the risk of wildfires by lowering the build-up of dry fuels, improving forest health, and controlling the growth of plants and insects. One of the crucial components that affects the execution of prescribed burns and controls the fire behaviour and smoke dispersal thereafter is the fuel moisture content, which needs to be considered when planning prescribed burns. The fuel moisture content variation is dependent on the meteorological variables, fuel properties, and the local turbulent fire dynamics, and so varies spatially and temporally over the land area before and during the fire advancement. In previous studies, the fuel moisture content was treated based on average properties, independent of the effect of local turbulence. In this study, the spatiotemporally varying fuel moisture content is obtained by a physics-based model that considers the coupled energy and moisture balance dynamics inside the fuel layers. This moisture model is implemented into the Wildland-urban Interface Fire Dynamics Simulator (WFDS) by means of a two-way coupling. Along with the local fuel properties, the model uses the instantaneous solar radiation and relative humidity, together with the instantaneous turbulent wind velocity and ambient air temperature at the boundary of each fuel sub-surface (grid) in the simulation domain. The coupled model is employed to study the effect of the dynamic variations of the fuel moisture on the turbulent evolution of the fire plume during a line fire propagation over a flat grassland. The findings of the study will provide insights into the effect of the fuel moisture content on the plume dynamics and smoke dispersal during prescribed burns and will assist in planning these burns.