Extreme fire behaviour

“Extreme” implies a level of fire behaviour characteristics that ordinarily precludes methods of direct control action. Such fires behave erratically, sometimes dangerously.

US National wildfire coordinating group glossary

Extreme fire behaviour may include:
– High rate of spread
– Prolific crowning
– Massive spotting
– Fire whirls
– Strong convection column

US national wildfire coordinating group glossary

Plume dynamics & the atmosphere

Plume dynamics refer to the flow of air related to a wildfire’s updraft and the way that the updraft changes over time.

Plume dynamics matter to extreme fire behaviour since they can accelerate surface winds and can transport the wind, temperature and moisture conditions above the ground down to the ground, where the wildfire is.

The aboveground environmental conditions may or may not differ from surface conditions, and their downward transport can result in unexpected changes in fire behaviour.

The structure and evolution of a wildfire’s plume is largely determined by the vertical structure of the atmosphere, which consequently exerts significant influence on fire behaviour.

Synoptic & sub-synoptic dynamics

Plume dynamics are largely affected by the vertical structure of the atmosphere, which in turn is determined by synoptic and sub-synoptic dynamics.

Processes related to synoptic dynamics control the transport of dry and/or high-momentum air downward to the lower middle troposphere. Related to the broader understanding of Rossby wave structures, these processes can be used for identifying/defining “fire fronts”; i.e., regions of the atmosphere that mark sharp transitions in fire behaviour.

Synoptic-scale processes can interact with processes taking place in the boundary or surface mixing layer. For instance, the development of the planetary boundary layer can bring the dry and high-momentum air of the middle atmosphere down to the ground, where a wildfire exists.

Our contribution

✔︎ FLAME will contribute to gaining a better understanding of the role that the synoptic and sub-synoptic dynamics of critical fire weather patterns play in the occurrence of extreme fire behaviour.

✔︎ High-resolution numerical simulations will be performed for selected wildfires that exhibited extreme fire behaviour.

✔︎ Numerical simulations will be analysed, focusing particularly on studying and characterising the dynamical processes related to the horizontal and vertical transport of dry, warm and high-momentum from the upper troposphere to the middle troposphere, and down to the ground.

✔︎ Traditional concepts and measures of synoptic and sub-synoptic dynamics, such as baroclinicity, low-level jets and potential vorticity advection, will be employed for deriving/revising conceptual models related to extreme fire behaviour (e.g., fire fronts) and its short-term prediction.