François Pimont

• French National Institute for Agriculture, Food, and Environment (INRAE)

Wind and slope are commonly accepted to be major environmental factors affecting the manner in which wildfires propagate. Fire-line width has been observed as having a significant effect on fire behaviour in some experimental fires. Most wildfire behaviour models and fire behaviour prediction systems take wind and slope effects into account when de...

Abstract Scientists and managers critically need ways to assess how fuel treatments alter fire behavior, yet few tools currently exist for this purpose. We present a spatially-explicit-fuel-modeling system, FuelManager, which models fuels, vegetation growth, fire behavior (using a physics-based model, FIRETEC), and fire effects. FuelManager's flexi...

Estimating leaf and plant area density with Terrestrial Laser Scanners (TLS) continues to be more and more popular, as tridimensional point clouds appear as an appealing measurement technique for heterogeneous environments. Some approaches implement a discretization of the point cloud in a grid (referred to as "voxel-based") to account for this veg...

Live fuel moisture content (LFMC) influences fire activity at landscape scale and fire behaviour in laboratory experiments. However, field evidence linking LFMC to fire behaviour are very limited, despite numerous field experiments. In this study, we reanalyse a shrubland fire dataset with a special focus on LFMC to investigate this counterintuitiv...

Modeling wildfire activity is crucial for informing science‐based risk management and understanding the spatiotemporal dynamics of fire‐prone ecosystems worldwide. Models help disentangle the relative influences of different factors, understand wildfire predictability, and provide insights into specific events. Here, we develop Firelihood, a two‐co...

Large-scale mapping of fuel load and fuel vertical distribution is essential for assessing fire danger, setting strategic goals and actions, and determining long-term resource needs. The Airborne LiDAR system can fulfil such goal by accurately capturing the three-dimensional arrangement of vegetation at regional and national scales. We developed a...

Key Message Understanding the impact of extreme drought on the canopy fuel moisture content ( CFMC ) is crucial to anticipate the effects of climate change on wildfires. Our study demonstrates that foliage mortality, caused by leaf embolism, can substantially diminish CFMC during drought on Pinus halepensis Mill. and Quercus ilex L. It emphasizes t...

Species mixture is promoted as a crucial management option to adapt forests to climate change. However, there is little consensus on how tree diversity affects tree water stress, and the underlying mechanisms remain elusive. By using a greenhouse experiment and a soil-plant-atmosphere hydraulic model, we explored whether and why mixing the isohydri...

Large-scale mapping of fuel load and structure is of great importance for assessing fire danger, setting strategic goals and actions, and determining long-term resource needs. The Airborne LiDAR system (ALS) can fulfill such goal, because it accurately captures the three-dimensional arrangement of vegetation at regional and national scales. We deve...

Plant hydraulics is crucial for assessing the plants' capacity to extract and transport water from the soil up to their aerial organs. Along with their capacity to exchange water between plant compartments and regulate evaporation, hydraulic properties determine plant water relations, water status and susceptibility to pathogen attacks. Consequentl...

Forest ecosystems are increasingly threatened by anthropogenic pressures, especially by the increase in drought frequency and intensity. Tree species mixtures could improve resilience to diverse global anthropogenic pressures. However, there is still little consensus on how tree diversity affects water stress. Although some studies suggest that mix...

Plain Language Summary Pyroregions represent the typical range of area burned, fire frequency, intensity, and seasonality that prevail in a region over long periods of time. Pyroregions are thus of great interest given their potential utility to determine regional fire patterns and foresee future alterations in response to global warming. Previous...

Vapor Pressure Deficit (VPD, atmospheric drought) and soil water potential (Ψsoil, soil drought) have both been reported to affect terrestrial plant water stress, plant functions (growth, stomatal conductance, transpiration) and vulnerability to ecosystem disturbances (mortality or vulnerability to wildfires). Which of atmospheric drought or soil d...

Wildfires are a global crisis, but current fire models fail to capture vegetation response to changing climate. With drought and elevated temperature increasing the importance of vegetation dynamics to fire behavior, and the advent of next generation models capable of capturing increasingly complex physical processes, we provide a renewed focus on...

Background Identifying if and how climatic and non-climatic factors drive local changes in fire regimes is, as in many other human-dominated landscapes, challenging in south-eastern France where both heterogeneous spatial patterns and complex fire trends are observed. Aim We sought to identify the factors driving the spatial-temporal patterns of f...

Fuel moisture content (FMC) is a crucial driver of forest fires in many regions world‐wide. Yet, the dynamics of FMC in forest canopies as well as their physiological and environmental determinants remain poorly understood, especially under extreme drought. We embedded a FMC module in the trait‐based, plant‐hydraulic SurEau‐Ecos model to provide in...

Background An increase in fire weather is expected in a warming climate, but its translation to fire activity (fire numbers and sizes) remains largely unknown. Additionally, disentangling the extent to which geographic and seasonal extensions as well as intensification contribute to future fire activity remain largely unknown. Aims We aimed to ass...

Unoccupied aerial vehicle laser scanning (UAV-LS) has been increasingly used for forest structure assessment in recent years due to the potential to directly estimate individual tree attributes and availability of commercial solutions. However, standardised procedures for campaign planning are still largely missing. This study investigated scanner...

Wildland fire is expected to increase in response to global warming, yet little is known about future changes to fire regimes in Europe. Here, we developed a pyrogeography based on statistical fire models to better understand how global warming reshapes fire regimes across the continent. We identified five large-scale pyroregions with different lev...

Plant area density (PAD in m²·m⁻³) defines the total one-sided total plant surface area within a given volume. It is a key variable in characterizing exchange processes between the atmosphere and land surface. Terrestrial laser scanning (TLS) provides unprecedented detail of the 3D structure of forest canopies. Yet, signal occlusion and uneven samp...

A widespread increase in tree mortality has been observed around the globe, and this trend is likely to continue because of ongoing climate-induced increases in drought frequency and intensity. This raises the need to identify regions and ecosystems that are likely to experience the most frequent and significant damage. We present SurEau-Ecos, a tr...

Wildland fires are among the most complicated environmental phenomena to model. Fire behavior models are commonly used to predict the direction and rate of spread of wildland fires based on fire history, fuel, and environmental conditions; however, more sophisticated computational fluid dynamic models are now being developed. This quantitative anal...

Under the influence of climate change, wildfire regimes are expected to intensify and expand to new areas, increasing threats to natural and socioeconomic assets. We explore the environmental and economic implications for the forest sector of climate-induced changes in wildfire regimes. To retain genericity while considering local determinants, we...

A widespread increase in tree mortality has been observed around the globe, and this trend is likely to continue because of ongoing climate-induced increases in drought frequency and intensity. This raises the need to identify regions and ecosystems that are likely to experience the most frequent and significant damages. We present SurEau-Ecos, a t...

O período entre 2018 e 2022 mostrou-nos que o problema dos incêndios à escala global não está a diminuir, antes pelo contrário. Parece que as consequências das alterações climáticas já estão a afectar a ocorrência de incêndios florestais em várias partes do Mundo, de uma forma que só esperaríamos que acontecesse vários anos mais tarde. Em muitos pa...

O período entre 2018 e 2022 mostrou-nos que o problema dos incêndios à escala global não está a diminuir, antes pelo contrário. Parece que as consequências das alterações climáticas já estão a afectar a ocorrência de incêndios florestais em várias partes do Mundo, de uma forma que só esperaríamos que acontecesse vários anos mais tarde. Em muitos pa...

O período entre 2018 e 2022 mostrou-nos que o problema dos incêndios à escala global não está a diminuir, antes pelo contrário. Parece que as consequências das alterações climáticas já estão a afectar a ocorrência de incêndios florestais em várias partes do Mundo, de uma forma que só esperaríamos que acontecesse vários anos mais tarde. Em muitos pa...

Key message A new process-based model, SurEau , is described. It predicts the risk of xylem hydraulic failure under drought. Context The increase in drought intensity due to climate change will accentuate the risk of tree mortality. But very few process-based models are currently able to predict this mortality risk. Aims We describe the operating...

Accurate spatiotemporal modeling of conditions leading to moderate and large wildfires provides better understanding of mechanisms driving fire-prone ecosystems and improves risk management. We study daily summer wildfire data for the French Mediterranean basin during 1995--2018. We jointly model occurrence intensity and wildfire sizes by combining...

The need for fine scale description of vegetation structure is increasing as Leaf Area Density (LAD, m²/m³) becomes a critical parameter to understand ecosystem functioning and energy and mass fluxes in heterogeneous ecosystems. Terrestrial Laser Scanning (TLS) has shown great potential for retrieving the foliage area at stand, plant or voxel scale...

The distribution of fuels is recognised as a key driver of wildland fire behaviour. However, our understanding of how fuel density heterogeneity affects fire behaviour is limited because of the challenges associated with experiments that isolate fuel heterogeneity from other factors. Advances in fire behaviour modelling and computational resources...

Turbulent flows over forest canopies have been successfully modeled using Large-Eddy Simulations (LES). Simulated winds result from the balance between a simplified pressure gradient forcing (e.g., a constant pressure-gradient or a canonical Ekman balance) and the dissipation of momentum, due to vegetation drag. Little attention has been paid to th...

Wildfire activity is expected to increase across the Mediterranean Basin because of climate change. However, the effects of future climate change on the combinations of atmospheric conditions that promote wildfire activity remain largely unknown. Using a fire-weather based classification of wildfires, we show that future climate scenarios point to...

Terrestrial Laser Scanning (TLS) has been used during the past decade to capture the complexity of 3D forest canopy structures, especially Leaf or Plant Area Density (LAD/PAD). TLS data, i.e. point cloud, can be divided into voxels to estimate the three-dimensional distribution of LAD/PAD. However, the combination effects of vegetation occlusion an...

Water content in living vegetation (or live fuel moisture content, LFMC), is increasingly recognized as a key factor linked to vegetation mortality and wildfire ignition and spread. Most often, empirical indices are used as surrogates for direct LFMC measurements. In this paper, we explore the functional and ecophysiological drivers of LFMC during...

Global warming is expected to increase droughts and heatwaves, and consequently fire danger in southern Europe in the forthcoming decades. However, an assessment of the uncertainties associated with this general trend at regional scales, relevant to decision-making, is still missing. This study aims at assessing potential climate change impacts on...

Modelling wildfire activity is crucial for informing science-based risk management and understanding fire-prone ecosystem functioning worldwide. Models also help to disentangle the relative roles of different factors, to understand wildfire predictability or to provide insights into specific events. Here, we develop a two-component Bayesian hierarc...

We describe the operating principle of the detailed version of the soil-plant-atmosphere model SurEau that allows, among other things, to predict the risk of hydraulic failure under extreme drought. It is based on the formalization of key physiological processes of plant response to water stress. The hydraulic functioning of the plant is at the cor...

Anthropogenic climate change is widely thought to have enhanced fire danger across parts of the world, including Mediterranean regions through increased evaporative demand and diminished precipitation during the fire season. Previous efforts have detected increases in fire danger across parts of southern Europe but a formal attribution of the role...

Une recrudescence des incendies extrêmes est observée sur tous les continents. Trois principaux facteurs aggravants sont discutés. La croissance démographique et l’étalement urbain augmentent l’exposition des biens et des personnes, et multiplient les mises à feu accidentelles. Les changements d’usage des sols favorisent le développement de la biom...

Key message Wildfire danger and burnt areas should increase over the century in southern Europe, owing to climate warming. Fire-prone area expansion to the north and to Mediterranean mountains is a concern, while climate-induced burnt area increase might be limited by fuel availability in the most arid areas. Further studies are needed to both asse...

Wildfire activity is expected to increase across the Mediterranean Basin because of climate change. However, the effects of future climate changes on the combinations of atmospheric conditions that promote large wildfires remain largely unknown. Using a fire-weather based classification of wildfires, we show that future climate scenarios point to a...

Wildfire is the main disturbance in forested ecosystems of southern Europe and is due to complex interactions between climate-weather, fuels and people. Warmer and drier conditions projected in this region are expected to profoundly affect wildfires, which will impact ecosystems and humans. We review the scientific literature addressing the assessm...

Inter-individual variability of tree drought responses within a stand has received little attention. Here we explore whether the spatial variations in soil/subsoil properties assessed through electrical resistivity tomography (ERT) could explain variations in drought response traits among trees.  We used ERT to compute the percent variation in res...

The spatial distribution of Leaf Area Density (LAD) in a tree canopy has fundamental functions in ecosystems. It can be measured through a variety of methods, including voxel-based methods applied to LiDAR point clouds. A theoretical study recently compared the numerical errors of these methods and showed that the bias-corrected Maximum Likelihood...

Dans les 32 départements les plus méridionaux de la France, le code forestier impose le débroussaillement des lieux habités, de leurs abords, et des réseaux qui les desservent, ainsi que diverses autres mesures de prévention des incendies de forêts. L'Obligation légale de débroussaillement, ou OLD, stipulée dans l'article L.134-6 du Code forestier,...

The amount and spatial distribution of foliage in a tree canopy have fundamental functions in ecosystems as they affect energy and mass fluxes through photosynthesis and transpiration. They are usually described by the Leaf Area Index (LAI) and the Leaf Area Density (LAD), which can be measured through a variety of methods, including voxel-based me...

In this presentation, we show that Live Fuel Moisture Content has a significant impact on both fire occurrence, size and spread rate in Southern France, when LFMC is lower than 100% of the dry mass. Our findings are consistent with levels used by operational services to rate fire danger (67, 54 and 43%). Our results suggest that more fire experimen...

According to climate projections, global warming is associated with increasing temperatures and dry spells in some parts of the world, especially the Mediterranean area. However, it is quite challenging for the scientific community to assess the intensity of these changes, because (i) the trend relies on the greenhouse gases (GHG) emission scenario...

Identifying the links between fire danger metrics and fire activity is critical in various operational and research fields. A common methodology consists in analysing the relationship between cumulative burnt areas and fire danger metrics. Building on this approach, it has been proposed that fuel moisture content (FMC) drives fire activity in some...

According to climate projections, global warming is associated with increasing temperatures and dry spells in some parts of the world, especially the Mediterranean area. This climate change has already triggered increases in wildfire danger and fire season length in Southern Europe and is expected to amplify in the forthcoming decades. However, it...

Live Fuel Moisture Content (LFMC)-the ratio of water mass to the dry mass of live fuel-is a critical factor of fire behavior and hazard. This parameter is largely controlled by weather conditions and is affected by climate changes. There is therefore an increasing need, to understand its variability, to improve its predictability and its impact on...

Fire experiments generally aim to relate fire behavior to fuel and weather conditions. One of the main factors influencing the fire rate of spread is the wind speed, but its measurement in fire experiments is challenging due to the combination of wind-flow turbulence and the remote location of the sensors relative to the fire front. Differences ari...

Live fuel moisture content (LFMC) influences fire activity at landscape scale and fire behavior in laboratory experiments. However, field evidences linking LFMC to fire behavior are very limited despite numerous field experiments. In the present study, we reanalyze a shrubland fire dataset with a special focus on LFMC to explain this counterintuiti...

Turbulent flows over and within forest canopies have recently been modeled with success using Large Eddy Simulations (LES). Validation exercises against experimental data suggest that models can be applied with a high degree of confidence for many applications, mechanical and physiological plant/atmosphere interaction analysis, seed or pollen dispe...

Reliable measurements of the 3D distribution of Leaf Area Density (LAD) in forest canopy are crucial for describing and modelling microclimatic and eco-physiological processes involved in forest ecosystems functioning. To overcome the obvious limitations of direct measurements, several indirect methods have been developed, including methods based o...

The original version of this article has been corrected to reflect Open Access. Additionally, this correction stands to correct what was a broken hyperlink in the key message section of the article as well as an error related to the replacement of Supplementary File 13595_2018_729_MOESM2_ESM.xlsx.

Monitoring live fuel moisture content (LFMC) in Mediterranean area is of great importance for fire risk assessment. LFMC has extensively been estimated based on optical remote sensing data. But the latter can be affected by atmospheric effects. As a complementary data source, microwave data can be used as they are relatively insensitive to atmosphe...

Key message: We model the dynamics of fuel characteristics in shrub strata dominated byQuercus cocciferaL. with data gathered in available literature. The model expresses the variability of this important fire-prone fuel type thanks to yield classes, and it can be used to investigate management scenarios. The approach could easily be applied to oth...

Key messageWe describe a modeling system that enables detailed, 3D fire simulations in forest fuels. Using data from three sites, we analyze thinning fuel treatments on fire behavior and fire effects and compare outputs with a more commonly used model.ContextThinning is considered useful in altering fire behavior, reducing fire severity, and restor...

The original article shows unit errors in Table 2: The torching index (TI) and crowning index (CI).

Keywords: Microwave remote sensing, Optical remote sensing, Root zone soil moisture, Vegetation optical depth, Live fuel moisture content, Fire risk, LFMC, VOD, VARI, NDVI, SAVI. ABSTRACT: Live fuel moisture content (LFMC) is an important factor in fire risk management in the Mediterranean region. Drawing upon a large network of stations (the Rése...

Fire experiments generally aim to relate fire behavior to fuel and weather conditions. One of the main factors influencing the fire rate of spread is the wind speed, but its measurement in fire experiments is challenging due to the combination of wind-flow turbulence and the remote location of the sensors relative to the fire front. Differences ari...

According to climate projections, global warming is associated with increasing temperatures and dry spells in some parts of the world, especially the Mediterranean area. This climate change has already triggered increases in wildfire danger and fire season length in Southern Europe and is expected to amplify in the forthcoming decades. However, it...

Previous studies have suggested that bark beetles and fires can be interacting disturbances, whereby bark beetle– caused tree mortality can alter the risk and severity of subsequent wildland fires. However, there remains considerable uncertainty around the type and magnitude of the interaction between fires following bark beetle attacks, especially...

9 Terrestrial LiDAR becomes more and more popular to estimate leaf and plant area density. 10 Voxel-based approaches account for this vegetation heterogeneity and significant work has 11 been done in this recent research field, but no general theoretical analysis is available. 12 Although estimators have been proposed and several causes of biases h...

Landscape heterogeneity shapes species distributions, interactions, and fluctuations. Historically, in dry forest ecosystems, low canopy cover and heterogeneous fuel patterns often moderated disturbances like fire. Over the last century, however, increases in canopy cover and more homogeneous patterns have contributed to altered fire regimes with h...

Interview de F. Pimont par Guillaume Aubertin de Var Matin le 6/9/2017 pour un article intitulé « Et si l’on plantait plus de vignes et d’oliviers pour limiter la propagation des incendies », pour publication le 9/9/2017

Canopy leaf biomass distribution is a factor of fire behaviour, which affects rate of spread, intensity and crown fire potential. At plot scale, the inventory-based approach combines a stem inventory, allometric equation for leaf mass and its vertical cumulative distribution to estimate leaf load and bulk density profile. This approach is still ver...

Scientists and managers need ways to assess how fuel treatments alter fire behavior, yet few tools currently exist for this purpose. FIRETEC and WFDS recently emerged as promising models in this context since they explicitly account for 3D fuel structure, but there is a need for a tool to facilitate the development of heterogeneous landscape-scale...

After publication of the research paper [1] an error during the data analysis process was recognized. [...]

Past fire recurrence impacts the vegetation structure, and it is consequently hypothesized to alter its future fire behaviour. We examined the fire behaviour in shrubland-forest mosaics of southeastern France, which were organized along a range of fire frequency (0 to 3-4 fires along the past 50 years) and had different time intervals between fires...

Highlights: We propose a method to estimate 3D leaf bulk density distribution, based on the calibration of density indices derived from T-LiDAR over small spherical volumes in which vegetation was sampled. The LiDAR-based bulk density distribution compared well to the inventory-based profiles in the upper part of the canopy.

Leaf biomass distribution is a key factor for modeling energy and carbon fluxes in forest canopies and for assessing fire behavior. We propose a new method to estimate 3D leaf bulk density distribution, based on a calibration of indices derived from T-LiDAR. We applied the method to four contrasted plots in a mature Quercus pubescens forest. Leaf b...

Modeling the behavior of crown fires is challenging due to the complex set of coupled processes that drive the characteristics of a spreading wildfire and the large range of spatial and temporal scales over which these processes occur. Detailed physics-based modeling approaches such as FIRETEC and the Wildland Urban Interface Fire Dynamics Simulato...

Ce numéro d’Innovations Agronomiques rassemble les présentations du colloque « Adaptation des forêts méditerranéennes aux changements climatiques » qui s'est tenu en Avignon le 20 novembre 2015