Reaction intensity partitioning: a new perspective of the National Fire Danger Rating System Energy Release Component

Francis M Fujioka,Menas C Kafatos,Shyh-Chin Chen,Seung Hee Kim,David R Weise

doi:10.1071/wf20025

Francis M Fujioka, Menas C Kafatos + Show 3 more

Open Access

https://doi.org/10.1071/wf20025

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Abstract

The Rothermel fire spread model provides the scientific basis for the US National Fire Danger Rating System (NFDRS) and several other important fire management applications. This study proposes a new perspective of the model that partitions the reaction intensity function and Energy Release Component (ERC) equations as an alternative that simplifies calculations while providing more insight into the temporal variability of the energy release component of fire danger. We compare the theoretical maximum reaction intensities and corresponding ERCs across 1978, 1988 and 2016 NFDRS fuel models as they are currently computed and as they would be computed under the proposed scheme. The advantages and disadvantages of the new approach are discussed. More study is required to determine its operational implications.

Highlights

50 years after it first appeared, the Rothermel fire spread model (Rothermel 1972) is still widely used in wildland fire danger and fire behaviour analysis and prediction in the US and elsewhere
In the US, the initial purpose of the model was to serve as the basis for the National Fire Danger Rating System (NFDRS; Deeming et al 1972, 1977; Bradshaw et al 1984; Cohen and Deeming 1985; Burgan 1988), which continues to the present
There is a substantial difference between fire danger and fire behaviour applications, which the US National Wildfire Coordinating Group describes as follows (NWCG 2002): ‘The principal difference is that fire danger is a broad-scale assessment while fire behavior is site-specific

Summary

Introduction

50 years after it first appeared, the Rothermel fire spread model (Rothermel 1972) is still widely used in wildland fire danger and fire behaviour analysis and prediction in the US and elsewhere. Rothermel’s approach was to determine a characteristic s from a weighting of the individual ss in the fuel bed, i.e. surface area weighting He used this s to calculate the optimum reaction velocity (Eqn 2), and subsequently to calculate reaction intensity and rate of spread Eqn 6, on the other hand, retains each s as uniquely representing the size class, the reaction intensity of each fuel component It represents the overall reaction intensity as the sum of partitioned single fuel fires – the term reaction intensity partitioning (RIP) – each burning according to its individual fuel characteristics, except that b, the packing ratio, is a function of all of the fuel loadings and bed depth.

Discussion and conclusions

Conflicts of interest