Sensitivity Experiments of the Local Wildland Fire with WRF-Fire Module

Abstract

In this paper, it is discussed the performance of the Weather Research and Forecasting (WRF) model coupled with a wildland fire-behavior module (WRF-Fire model) by the observational data collected in an experiment with a low-intensity prescribed fire (LIPF) conducted in the New Jersey Pine Barrens (NJPB) on March 6, 2012. The sensitivity experiments of the WRF-Fire model are carried out to investigate the interactions between the wildland fire and the atmospheric planetary boundary layer. The two-way WRF-Fire model conofigured with fire and large eddy simulation (LES) mode is used to explore the fire characteristics of perimeter shape, intensity, spread direction and external factors of wind speed, and to discuss how these external parameters affect the fire, and the interactions between the atmosphere and fire. Results show that the sensitive experiments can provide the meteorological elements close to observations, such as the temperatures, winds and turbulent kinetic energy near the surface in the vicinity of the fire. The simulations also can reproduce the fire spread shape and speed, fire intensity, and heat flux released from fire. From the view of energy, the heat flux feed back to the atmospheric model and heat the air near the surface, which will induce strong thermal and dynamic instability causing strong horizontal convergence and updraft, and form the fire-induced convective boundary layer. The updraft will be tilted downstream of the fire area based on the height of the ambient winds. Due to the effect of the this updrafts, the particles and heat from the fuel combustion can be transported to the downwind and lateral regions of the fire area. Meanwhile, there is a downdraft flow with higher momentum nearby the fire line transporting fresh oxygen to the near surface, which will increase winds behind the fire line, accelerate the rate of spread (ROS) and make the fire spread to a larger area. Ultimately, a fire-induced climate is established.