Graham Mills

Variability and drivers of extreme fire weather in fire-prone areas of south-eastern Australia

Most of the life and property losses due to bushfires in south-eastern Australia occur under extreme fire weather conditions – strong winds, high temperatures, low relative humidity (RH) and extended drought. However, what constitutes extreme, and the values of the weather ingredients and their variability, differs regionally. Using a gridded dataset to identify the highest 10 fire weather days from 1972 to 2012, as defined by McArthur’s Forest Fire Danger Index (FFDI), for 24 sites across Victoria and nearby, we analyse the extent and variability of these highest 10 FFDI days, and of the contributing temperature, RH, wind speed, wind direction and drought indices. We document the occurrence of these events by time of day, month of occurrence and inter-annual variability. We find there is considerable variability among regions in the highest FFDI days and also the contributing weather and drought parameters, with some regional groupings apparent. Many major fire events occurred on these highest 10 fire weather days; however there are also days in which extreme fire weather occurred yet no known major fires are recorded. The results from this study will be an additional valuable resource to fire agencies in fire risk planning by basing fire management decisions on site-specific extreme fire weather conditions.

Fire-Modified Meteorology in a Coupled Fire–Atmosphere Model

AbstractThe 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 fluxe...

A bias corrected WRF mesoscale fire weather dataset for Victoria, Australia 1972-2012

Climatology data of fire weather across the landscape can provide science-based evidence for informing strategic decisions to ameliorate the impacts (at times extreme) of bushfires on community socio-economic wellbeing and to sustain ecosystem health and functions. A longterm climatology requires spatial and temporal data that are consistent to represent the landscape in sufficient detail to be useful for fire weather studies and management purposes. To address this inhomogeneity problem for analyses of a variety of fire weather interests and to provide a dataset for management decision-support, a homogeneous 41-year (1972-2012), hourly interval, 4 km gridded climate dataset for Victoria has been generated using a combination of mesoscale modelling, global reanalysis data, surface observations, and historic observed rainfall analyses. Hourly near-surface forecast fields were combined with Drought Factor (DF) fields calculated from the Australian Water Availability Project (AWAP) rainfall analyses to generate fields of hourly fire danger indices for each hour of the 41-year period. A quantile mapping (QM) bias correction technique utilizing available observations during 19962012 was used to ameliorate any model biases in wind speed, temperature and relative humidity. Extensive evaluation was undertaken including both quantitative and case study qualitative assessments. The final dataset includes 4-km surface hourly temperature, relative humidity, wind speed, wind direction, Forest Fire Danger Index (FFDI), and daily DF and Keetch-Byram Drought Index (KBDI), and a 32-level full three-dimensional volume atmosphere.

Chapter 23 Managing Smoke from Wildfires and Prescribed Burning in Southern Australia

In Australia the responsibility for management of forests and other public lands rests largely with state governments, and multiple government agencies may be involved in fire management. Whether resulting from wildfire, fuel reduction, or silvicultural operations, biomass burning often stimulates community concerns about hazards from fine particulates and chemical compounds contained in smoke. Management practices and community perceptions of smoke from biomass burning differ from region to region according to social and environmental factors. Recognition of the need for a response to concerns has led to the development of a smoke management research program within the Bushfire Cooperative Research Centre, in conjunction with fire and land management agencies and the Australian Bureau of Meteorology (the Bureau). This program aims to assist land management planning by predicting where smoke from scheduled burns would be transported, thus providing the opportunity to avoid burning in situations where there is potential for adverse community impact. The primary tool provided is a dispersion model forecast using input from the Bureau’s operational mesoscale numerical weather prediction (NWP) models. Decision tools are applied in a similar manner for prescribed burning and wildfires and have been used by agencies to provide community advice and to avoid smoke hazards during aircraft operations. We investigated strategies used by land management agencies to minimize community impact of smoke from prescribed burns, and studied the way in which the dispersion model forecasts are integrated into their decision support systems.

Coupled Fire–Atmosphere Simulations of the Rocky River Fire Using WRF-SFIRE

AbstractThe coupled atmosphere–fire spread model “WRF-SFIRE” has been used to simulate a fire where extreme fire behavior was observed. Tall flames and a dense convective smoke column were features of the fire as it burned rapidly up the Rocky River gully on Kangaroo Island, South Australia. WRF-SFIRE simulations of the event show a number of interesting dynamical processes resulting from fire–atmosphere feedback, including the following: fire spread was sensitive to small changes in mean wind direction; fire perimeter was affected by wind convergence resulting from interactions between the fire, atmosphere, and local topography; and the fire plume mixed high-momentum air from above a strong subsidence inversion. At 1-min intervals, output from the simulations showed fire spread exhibiting fast and slow pulses. These pulses occurred coincident with the passage of mesoscale convective (Rayleigh–Benard) cells in the planetary boundary layer. Simulations show that feedback between the fire and atmosphere may...