Carbon dioxide and particulate emissions from the 2013 Tasmanian firestorm: implications for Australian carbon accounting

Abstract

Background: Uncontrolled wildfires in Australian temperate Eucalyptus forests produce significant smoke emissions, particularly carbon dioxide (CO₂) and particulates. Emissions from fires in these ecosystems, however, have received less research attention than the fires in North American conifer forests or frequently burned Australian tropical savannas. Here, we use the 2013 Forcett-Dunalley fire that caused the first recorded pyrocumulonimbus event in Tasmania, to understand CO₂ and particulate matter (PM_2.5) emissions from a severe Eucalyptus forest fire. We investigate the spatial patterns of the two emissions using a fine scale mapping of vegetation and fire severity (50 m resolution), and utilising available emission factors suitable for Australian vegetation types. We compare the results with coarse-scale (28 km resolution) emissions estimates from Global Fire Emissions Database (GFED) to determine the reliability of the global model in emissions estimation.

Results: The fine scale inventory yielded total CO₂ emission of 1.125 ± 0.232 Tg and PM_2.5 emission of 0.022 ± 0.006 Tg, representing a loss of 56 t CO₂ ha^-1 and 1 t PM_2.5 ha^-1. The CO₂ emissions were comparable to GFED estimates, but GFED PM_2.5 estimates were lower by a factor of three. This study highlights the reliability of GFED for CO₂ but not PM_2.5 for estimating emissions from Eucalyptus forest fires. Our fine scale and GFED estimates showed that the Forcett-Dunalley fire produced 30% of 2013 fire carbon emissions in Tasmania, and 26-36% of mean annual fire emissions for the State, representing a significant single source of emissions.

Conclusions: Our analyses highlight the need for improved PM_2.5 emission factors specific to Australian vegetation, and better characterisation of fuel loads, particularly coarse fuel loads, to quantify wildfire particulate and greenhouse gas emissions more accurately. Current Australian carbon accountancy approach of excluding large wildfires from final GHG accounts likely exaggerates Tasmania's claim to carbon neutrality; we therefore recommend that planned and unplanned emissions are included in the final national and state greenhouse gas accounting to international conventions. Advancing these issues is important given the trajectory of more frequent large fires driven by anthropogenic climate change.

Keywords: Carbon; Emission; Eucalyptus; FullCAM; GFED; Particulate; PyroCb; Smoke; Wildfire.