Yanchep bushfire analysis

The Yanchep bushfire occurred in 11-15 December 2019 and was one of several noteworthy bushfires in Western Australia during the summer period. This bushfire coincided with some of the worst fire behaviour in NSW and Victoria and all were influenced by related climate processes.   The Yanchep bushfire burned over ~12,300 ha spanning a diverse range of vegetation types (coastal dunes and heath, limestone heath, woodlands) and fire management histories. 

Despite rapidly expanding literature on fire severity classification, drivers of fire behaviour, and other important operational considerations key knowledge gaps remain in Western Australia.  The Yanchep bushfire represents an excellent opportunity to develop fire knowledge for the Western Australia fire community and contribute to growing local fire science capacity.  This project sought to classify fire severity using two complementary approaches, map vegetation at a finer scale than previously available, determine baseline biomass and fuel loads across key vegetation types, and assess the roles of fire weather, vegetation, and prior management in determining fire severity.

We were able to classify fire severity successfully (with 78% accuracy) using both field-based training data as well as a battery of remote sensing metrics.  Vegetation mapping using soil types and field validation yielded a higher quality map than previously available.  Fuel load estimates provide an important range of values across vegetation types and fire histories.  Lastly, examining bushfire severity in relation to prior fire, fire weather, and vegetation type showed clear interactions of previous fire in the prior 2-3 years,with beach-associated vegetation burning at lower severity, and limestone heath burning at higher severity. 

Collectively, these characteristics provide key insights for end-users in WA and more broadly, enabling fire severity mapping, informing fire operations, providing finer grained vegetation maps and fuel loads, and enabling an understanding of how prescribed burning in coastal plain vegetation types can influence bushfire spread and suppression.  

Future applications of this work will hopefully include:

1. Fire severity mapping across the Swan Coastal Plain and then the entirety of the southwestern conservation estate managed by DBCA and eventually all land tenures. 
2. Scaling up this proof of concept work to update vegetation maps and associated fuel load estimates in the Perth region.  Such products are urgently needed by end-user organisations such as DFES, DBCA, and local government. 
3. The basic reconstruction analyses presented in this report can be readily extended to incorporate broader data sets and more nuanced analyses to reveal the interplay of vegetation type, fire history, and fuels-fuel moisture dynamics. 
4. Ecological feedbacks to fuel loads and bushfire hazard. Many areas experienced short interval fires and continued efforts can reveal the impact on vegetation regrowth and flow through effects on fuel loads and overall bushfire hazard (i.e. changed composition and structure effects on future bushfire hazard).