Capturing Plume Rise and Dispersion with WRF-Fire: an RxCADRE Case Study

The effects of wildfire smoke can cover a broad range of spatiotemporal scales and have a significant impact on regional air quality and human health. The buoyant phase of the smoke plume, which determines its final rise height, has a strong influence on pollutant concentrations downwind, and provides key input into global and regional chemical transport models. Lack of data for model evaluation is widely acknowledged to be the primary limiting factor in plume-rise model development and improvement. As detailed observations of turbulence, entrainment, and 3-D smoke concentrations are notoriously scarce, numerical models provide a valuable alternative to field studies with their ability to generate “synthetic data” for a wide range of conditions. In particular, large eddy simulations (LES) have proved useful in capturing turbulent boundary-layer processes, thereby presenting a viable approach to studying fire plume growth and dispersion. However, the ability of numerical models to simulate fire plume dynamics must still be evaluated with real-world observations.

Weather Research and Forecasting Model (WRF-Fire) allows two-way coupling of LES with a semi-empirical fire growth model. Several studies have examined the ability of WRF-Fire to capture the ground-spread behaviour of a fire line. Yet to the authors’ knowledge, no attempts have been made to assess the simulated fire plume dynamics. The recent Prescribed Fire Combustion and Atmospheric Dynamics Experiment (RxCADRE) provides detailed fuel, meteorological, and emissions data from a real prescribed burn. This presents a unique opportunity to perform a ground-truth comparison with WRF-Fire simulated plume rise and dynamics. In the current study, observations from RxCADRE are used to initialize the domain, as well as assess the accuracy of plume dispersion predictions.

Results highlight the strengths and limitations of using WRF-Fire for studying plume rise, and provide useful guidelines for modeling smoke dispersion with LES.