Plant hydraulic modelling of leaf and canopy fuel moisture content reveals increasing vulnerability of a Mediterranean forest to wildfires under extreme drought.

Fuel moisture content is a crucial driver of forest fires in many regions worldwide. Yet, the dynamics of fuel moisture content in forest canopies as well as their physiological and environmental determinants, remain poorly understood, especially under extreme drought We embedded a fuel moisture content module in the trait-based, plant hydraulic SurEau-Ecos model to provide innovative process-based predictions of leaf (LFMC) and canopy fuel moisture content (CFMC) based on leaf water potential (ψ Leaf ). SurEau-Ecos-FMC relies on pressure-volume (p-v) curves to simulate live fuel moisture content (LFMC) and vulnerability curves to cavitation to simulate foliage mortality. SurEau-Ecos-FMC accurately reproduced ψ Leaf and LFMC dynamics as well as the occurrence of foliage mortality in a Mediterranean Quercus ilex forest. Several traits related to water use (leaf area index, available soil water and transpiration regulation), vulnerability to cavitation and p-v curves (full turgor osmotic potential) had the greatest influence on LFMC and CFMC dynamics. As the climate gets drier, our results showed that drought-induced foliage mortality is expected to increase, thereby significantly decreasing CFMC. Our results represent an important advance in our capacity to understand and predict the sensitivity of forests to wildfires.