Fire-Modified Meteorology in a Coupled Fire–Atmosphere Model

Abstract

The coupled fire-atmosphere model consisting of the Weather and Forecasting (WRF) Model coupled with the fire-spread model (SFIRE) module has been used to simulate a bushfire at D'Estrees Bay on Kangaroo Island, South Australia, in December 2007. Initial conditions for the simulations were provided by two global analyses: the GFS operational analysis and ERA-Interim. For each NWP initialization, the simulations were run with and without feedback from the fire to the atmospheric model. The focus of this study was examining how the energy fluxes from the simulated fire modified the local meteorological environment. With feedback enabled, the propagation speed of the sea-breeze frontal line was faster and vertical motion in the frontal zone was enhanced. For one of the initial conditions with feedback on, a vortex developed adjacent to the head fire and remained present for over 5 h of simulation time. The vortex was not present without fire-atmosphere feedback. The results show that the energy fluxes released by a fire can effect significant changes on the surrounding mesoscale atmosphere. This has implications for the appropriate use of weather parameters extracted from NWP and used in prediction for fire operations. These meteorological modifications also have implications for anticipating likely fire behavior.

Some Requirements for Simulating Wildland Fire Behavior Using Insight from Coupled Weather—Wildland Fire Models

“…Numerous studies (e.g., [15,17,[56][57][58][59]63,64] and others) have applied coupled weather-fire models to simulate large wildland fire events. The standard approach, taken from NWP, is to begin with a regional model domain with the approximate grid spacing of a larger-scale forecast or analysis product, either of which may provide initial and boundary conditions (10-12 km).…”

“…Excessive dissipation at fine scales smooths out these fine gradients and distorts the development of larger-scale motions. Weaknesses in the ability to meet these criteria explain the unnaturally weak vortices produced by [15] (in contrast to [16], where WRF is configured in LES mode or [9]), despite ample heat fluxes along a shear zone-prime conditions for fire whirl formation.…”

“…Previous work has already demonstrated the unfolding of a wildfire including timing of important transitions and distinctive shape, and emergence of transient fire phenomena including wind shifts [12], fire whirls [13][14][15][16], and horizontal roll vortices [17]. These advances were attributed to resolving the intricate, time-varying airflow in mountainous terrain at spatial resolutions of about one hundred meters and including fire-atmosphere feedbacks exemplified by plume dominated fires.…”

WRF and SFIRE simulations of the Layman fuel reduction burn

“…The model configuration is described in Peace (2014) and Peace et al (2015). A brief summary is included here for completeness.…”

“…This study is the third in a series of three using WRF and SFIRE to examine Australian case studies of events where unusual fire activity occurred. The first two studies are detailed in Peace (2014) and Peace et al (2015).…”