The Destructive Sir Ivan Fire in New South Wales, Australia; Simulations Using a Coupled Fire—Atmosphere Model

Abstract

The destructive Sir Ivan Dougherty fire burned 55,000 hectares around 250 km northwest of Sydney in New South Wales on 12 February 2017. Record hot temperatures were recorded in the area during the lead-in days and the fire conditions at the time were described as the ‘worst ever seen in NSW’. The observed weather conditions were hot, dry and very windy ahead of a synoptic frontal wind change during the afternoon. ‘Extreme’ to ‘catastrophic’ fire weather was predicted, and the potential for extreme fire behaviour was identified several days in advance. The Australian coupled fire–atmosphere model ACCESS-Fire has been run to explore the characteristics of the Sir Ivan fire. Several features resulting from fire–atmosphere interaction are produced in the simulations. Simulated heat flux along the fire perimeter shows increased intensity on the northern fire flank in response to gradual backing winds ahead of the main frontal wind change. Temporal and spatial variability in fire activity, seen as pulses in fire intensity and fireline wind speed, develop in response to boundary layer rolls in the wind fields. Deep moist convection consistent with the observed pyrocumulonimbus (pyroCb) cloud is simulated over the fire at around the time of the frontal wind change, and matches guidance from the ‘PyroCb Firepower Threshold’ tool, which showed transient favourable conditions. After the wind change, short-lived near-surface and elevated vortices suggest organised rotating features on the northern flank of the fire. The coupled model captures processes that cannot be produced in uncoupled fire predictions and that are not captured in current operational meteorological forecast products provided to Australian fire agencies. This paper links the features from coupled simulations to available observations and suggests pathways to embed the learnings in operational practice.

Triggering Pyro-Convection in a High-Resolution Coupled Fire–Atmosphere Simulation

“…In the Waroona fire (January 2016), the coupled model produced a pyroCb cloud above the fire front, which extended to nearly a 15 km altitude [43]. In the Sir Ivan fire (February 2017), the simulations were able to generate deep moist convection extending up to a 12 km altitude [9]. Furthermore, the authors highlighted the sensitivity of deep moist convection to fuel load, and then to heat flux [9].…”

“…In the Sir Ivan fire (February 2017), the simulations were able to generate deep moist convection extending up to a 12 km altitude [9]. Furthermore, the authors highlighted the sensitivity of deep moist convection to fuel load, and then to heat flux [9]. Concerning the fuel moisture content, it has a small influence on the formation of pyro-clouds, with atmospheric moisture availability being the main factor favoring the development of these clouds [44].…”

“…These conditions are known to favor the development of pyro-cumulonimbus (pyroCb) clouds. PyroCb clouds are one of the main hazards associated with mega fires and directly affect the fire front propagation [7][8][9]. Such an environment represents significant challenges to firefighters and communities, especially when wildfires occur near an urban interface.…”

Fuel Drivers of Fire Behaviour in Coastal Mallee Shrublands

“…Physical fire models have been used to study the influence of fuel on fire spread [83][84][85]. Physical fire models continue to improve through the inclusion of additional data describing physical processes and become cheaper and faster to run [86][87][88][89]. However, field experiments and direct or indirect measurement of fuels will continue to play a key role in validation, whether for an empirical or physical model.…”