Forecasting smoke from a forty-day fire
Peat fires often smoulder for weeks, months or even years on end while all-the-time releasing plumes of hazardous smoke into the air. While they may not present the same immediate threat to lives and property as surface bushfires, peat fire do pose a very real health risk to surrounding communities. To help authorities better manage this risk, a team of researchers have adapted their Air Quality Forecasting System (AQFx) to this unique type of fire, with promising results.
A forty-day fire
On the 17th of March 2018, major grassland fires close to Cobden in south-west Victoria ignited several peat bogs. Three of the peat fires smouldered for the next 40 days, in some places at depths of over 1 metre. While the fire burned it generated large amounts of toxic smoke that typically remained at or close to the ground, severely impacting air quality in the area. Surrounding communities were exposed to significant concentrations of fine particles (PM2.5) and active interventions (such as relocation of schools) were required in order to protect vulnerable members of the population.
Forty days may seem a long time for a single fire to burn, but not by peat fire standards since peat fires are notoriously hard to put out. Peat soils are essentially partially decayed biomass and make up the world’s largest reserves of terrestrial organic carbon. Because of this dense accumulation of fuel, once ignited, peat fires burn for very long periods of time even in the face of extensive rains or fire-fighting attempts. The only ways to extinguish peat fires are either to dig them out, which can be no small task as they are often kilometres wide and metres deep, or to saturate the area, which often draws on huge amounts of water to re-establish groundwater levels and rehydrate the area.
A growing problem
In recent years there has been an increase in the occurrence of peat fires. This has resulted from wetlands and peat bogs drying out due to our warming climate and increased use of groundwater. Once dry, peat areas are highly vulnerable to ignition and can burn at increased depths.
Consequently, harmful smoke pollution events such as those experienced in Cobden, and more recently in Port Macquarie, NSW, in July 2019, and in Gippsland, VIC, in February 2020 are likely to become more frequent.
To help authorities better manage the potential impact of smoke from peat fires on surrounding communities, scientists from CSIRO’s Climate Science Centre have been working with the Department of Environment, Land, Water and Planning (DELWP), the Environmental Protection Authority (EPA) of Victoria, Emergency Management Victoria (EMV) and Country Fire Authority (CFA) to assess the performance of the AQFx in forecasting smouldering peat fires.
AQFx: The BOM-CSIRO Air Quality Forecasting System
AQFx was developed in response to an identified need for fire land-use managers to be able to factor in the health risk of smoke exposure when planning and implementing prescribed burning programs. CSIRO worked with Victoria’s DELWP, the Bureau of Meteorology (BOM), and the university sector to develop AQFx, which provides six-day ensemble fire weather forecasts, 24–60 hour detailed air pollution forecasts, and next-day prescribed burn smoke forecasts for Victoria (and more recently), for NSW.
AQFx is run operationally by BOM and uses a fire spread model to calculate smoke emissions from ongoing fires and planned burns (wind-blown dust and urban sources of pollution are also included in AQFx). The transport of smoke by the wind is forecast using the meteorology from BoM’s ACCESS weather forecasting system.
Although originally designed to provide guidance to fire land-use managers on how to minimise population exposure to smoke generated by fuel reduction burns, the applications of AQFx are growing. AQFx is now also being used to forecast smoke exposure from bushfires, with this information being made available to the emergency management centres and the state environment protection authorities. And with the emergence of smoke from peat fires as a growing threat to communities across Australia, the AQFx team have now turned their attention to this unique application.
A new application for AQFx
During the 2018 Cobden peat fires, air quality monitoring sites were set up by the Victorian EPA to enable emergency response agencies to inform the community about air quality in the area. The peat fires and the associated air quality monitoring provided a unique opportunity to review the capabilities of the Air Quality Forecasting System (AQFx) to track this unique type of smoke.
To forecast the smoke impacts from the peat fires, the research team modified the biomass burning emission module in AQFx to account for the different combustion process of a sub-surface peat fire as opposed to a planned burn (with flaming followed by smouldering of above-ground fuel). AQFx was also reconfigured to account for the finer spatial scales of smoke transport (10 -20 km).
A bottom-up approach was used to reconstruct the emission fields from the peat fires. The emissions of key air quality indicators, PM2.5 and carbon monoxide (CO), from the peat fires were estimated using information on the thermal activity of the peat fires by infrared line scan imagery, estimates of fuel load determined by the peat bulk density and depth of the peat, estimates of the fuel burning efficiency and patchiness, and emission rates of PM2.5 and CO derived from the literature.
AQFx PM2.5 forecasts were then compared with PM2.5 observations from the 10 incident monitoring sites set up by EPA Victoria in response to the peat fires. The AQFx model performance was evaluated against hourly and daily observations of PM2.5.
Encouragingly, AQFx was found to correctly identify most pollution events when 24-hour averaged PM2.5 concentrations exceeded the NEPM air quality standard of 25 μg/m3. Time series plots of hourly observed and modelled PM2.5 for the nearest model cell to the monitoring site showed that the high PM events were generally captured well. However, calm conditions, meso-scale meteorological transition events, and the close proximity of monitoring sites to the peat fires were the main challenges in regard to accurate forecasting.
Through this assessment the team also identified recommendations and a description of key opportunities for improvements in plume and smoke model systems for slow moving smouldering fires. These will be used to inform future investments and activities in research, training and model development.