A comparison of two coupled smoke modeling systems used for prediction of smoke dispersion and emissions from low-intensity wildland fires

Low-intensity wildland fires provide a unique challenge for researchers who use numerical models to predict smoke dispersion and emissions. Attributes such as topography, vegetation type, and micrometeorology affect the local dispersion of smoke. Current smoke dispersion modeling systems typically are comprised of an atmospheric model that is coupled to a smoke dispersion model. High-resolution output from these coupled systems may provide adequate detail to depict smoke dispersion from low-intensity fire scenarios, such as smoke lingering underneath the forest canopy of a low-intensity prescribed burn.

As part of a Joint Fire Science Program project that focuses on the development and validation of modeling tools for predicting smoke from low-intensity fires, we used a smoke dispersion model that is a modified version of a popular dispersion model. FLEXPART is an open-source dispersion model that was originally coupled to global climate models, but recent versions have allowed for coupling to regional climate models such as the Weather Research and Forecasting (WRF) model. Researchers at the Pacific Northwest National Laboratory (PNNL) made extensive modifications to FLEXPART source code in order to consider regional climate model coordinate systems, as well as additional options for turbulence and convection. Thus, the PNNL Integrated Lagrangian Transport (PILT) model is the version utilized here.

Observations were collected during a low-intensity prescribed burn at an experimental site in the New Jersey Pine Barrens. Smoke dispersion model runs were completed using the coupled system, PILT-WRF. Also considered was the Advanced Regional Prediction System (ARPS). A recently developed PILT-ARPS coupled system is now capable of including forest canopy and fire information that can affect local meteorological conditions and subsequent modeled dispersion. Information about fuel moisture, loading, consumption, and emissions was provided from observations and the use of the Fire Emission Production Simulator (FEPS). A comparison of smoke dispersion results is provided using PILT-WRF and also PILT-ARPS with and without introduced canopy and fire information. The fine-scale smoke dispersion and emission results from the coupled PILT-WRF and PILT-ARPS systems used in this study provide the initial foundation toward improved predictions of smoke transport and emissions from low-intensity fires, which will assist in the planning of future prescribed burns.