Published works

Vorticity-driven Lateral Spread, or VLS, is a form of dynamic bushfire propagation that involves rapid fire spread across steep, lee-facing slopes in a direction roughly perpendicular to the prevailing winds.

It is often accompanied by dense spotting downwind of the affected slope. These spot fires interact and coalesce, resulting in active flaming over large areas – a phenomenon known as ‘deep flaming’.

As such, VLS is a potent and dangerous pattern of bushfire propagation, which can quickly turn a small fire into a catastrophic large-scale event. The rapid rates of spread associated with VLS are a threat to firefighter safety and the deep flaming associated with VLS increases the likelihood of extreme bushfire development, including fire-generated thunderstorms, which are known in the scientific literature as pyrocumulonimbus.

This document describes an operational mapping overlay for identifying regions prone to VLS. This is prefaced with some discussion on VLS and dynamic fire behaviour more generally. The mapping overlay essentially filters wind and terrain information to identify parts of the landscape that satisfy the necessary conditions for VLS occurrence. They are intended to provide fire managers and fire behaviour analysts with an additional layer of information that can help them anticipate VLS occurrence and subsequent development of extreme bushfires. The use of the mapping overlay is demonstrated using a number of example cases studies.