Comment on “Classification and mapping of European fuels using a hierarchical, multipurpose fuel classification system” by Aragoneses et al. (2023)

Abstract. Classifying and mapping vegetation as fuel is essential for various fire research and management applications. Aragoneses et al. (2023) proposed a hierarchical fuel classification system for Europe and allocated standard fuel models to the resulting fuel types, producing a continental fuel map. We examine the methods involved and their outcomes. The reasoning behind their system is misguided, as the proposed set of fuel types does not reflect fuel-complex characteristics and the inherent fire behaviour. In their categorization of shrublands and grasslands, fuel depth is a key variable; however, the bioclimatic modelling approach used to map it is unreliable, as it is based on local empirical relationships. The adopted 1-km mapping resolution is one to two orders of magnitude lower than the needs of spatially-explicit fire behaviour simulation, and implied up-scaling procedures adding uncertainty due to loss of thematic detail. Finally, a simplistic aridity-based rule was applied to assign fuel models to fuel types, limiting the options available. This, in combination with fuel-depth overestimation and untenable fuel model choices, contributed to a substantial fire-hazard overestimation across the large portion of Europe occupied by low-flammability cover types.