Presentation description

Wildfires in the United States burned nearly 12,000 square miles in 2022, more than the area of Massachusetts. Computational wildfire models are an important tool for improving our understanding of fire behavior. Horizontal winds are one of the most critical drivers of fire spread; as a result, there is a need to assess and improve the accuracy of wildfire models in simulations with ambient winds. QES-Fire dynamically couples a simplified physics model of wildfire spread to a diagnostic, mass-conserving, fast-response wind model. QES-Fire calculates fire-induced wind fields using a plume model parameterized by fire heat release. Total wind is calculated by superimposing fire-induced winds onto ambient winds at every grid point. As a result, QES-Fire does not account for the tilting of fire-induced updrafts in ambient horizontal winds. To address this, we compare the simulation results of a fire with ambient crosswinds in QES-Fire to those obtained from a model which solves the full equations of motion, including momentum and energy processes, the System for Atmospheric Modeling (SAM). SAM is coupled to an identical fire spread and heat release model as in QES-Fire. To create a consistent heat source, the fuel heat release calculation in SAM is modified to allow for an infinite burn time. After the model reaches a steady state, a time-average of wind velocity fields is used for comparisons with QES-Fire to reduce the significance of turbulence in the plume. As QES-Fire does not account for loss of plume buoyancy due to atmospheric stability, comparisons between the two models are only made in lower sections of the atmosphere. Analysis of the plume wind fields includes comparisons between plume displacements and cross sections at multiple horizontal wind speeds. Discussion of the results introduces possible methods for parameterizing the effects of horizontal crosswinds on buoyant plumes.