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11. Increased likelihood of heat-induced large wildfires in the Mediterranean Basin

Author

Ruffault, J, Curt, T, Moron, V, Trigo, RM, Mouillot, F, Koutsias, N, Pimont, F, Martin-StPaul, NK, Barbero, R, Dupuy, J-L, Russo, A, Belhadj-Kheder, C, Institut méditerranéen de biodiversité et d'écologie marine et continentale (IMBE), Avignon Université (AU)-Aix Marseille Université (AMU)-Institut de recherche pour le développement [IRD] : UMR237-Centre National de la Recherche Scientifique (CNRS), Aix Marseille Université (AMU), Risques, Ecosystèmes, Vulnérabilité, Environnement, Résilience (RECOVER), Aix Marseille Université (AMU)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Universidade de Lisboa = University of Lisbon (ULISBOA), Centre d’Ecologie Fonctionnelle et Evolutive (CEFE), Université Paul-Valéry - Montpellier 3 (UPVM)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), University of Patras, Ecologie des Forêts Méditerranéennes (URFM), Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Université de la Manouba [Tunisie] (UMA), FCT (Fundação para a Ciência e a Tecnologia, Portugal) under project IMPECAF (PTDC/CTA-CLI/28902/2017), ANR-11-IDEX-0001,Amidex,INITIATIVE D'EXCELLENCE AIX MARSEILLE UNIVERSITE(2011), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Collège de France (CdF (institution))-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Universidade de Lisboa (ULISBOA), Université Paul-Valéry - Montpellier 3 (UPVM)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), and University of Patras [Patras]

Subjects
Heat induced, Ecology, 010504 meteorology & atmospheric sciences, Fire ecology, [SDE.MCG]Environmental Sciences/Global Changes, lcsh:R, Natural hazards, lcsh:Medicine, Climate change, 15. Life on land, 010501 environmental sciences, Future climate, 01 natural sciences, Mediterranean Basin, Article, Fire weather, 13. Climate action, Climatology, Environmental science, lcsh:Q, lcsh:Science, Climate-change impacts, 0105 earth and related environmental sciences
Abstract

International audience; 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 an increase in the frequency of two heat-induced fire-weather types that have been related to the largest wildfires in recent years. Heat-induced fire-weather types are characterized by compound dry and warm conditions occurring during summer heatwaves, either under moderate (heatwave type) or intense (hot drought type) drought. The frequency of heat-induced fire-weather is projected to increase by 14% by the end of the century (2071-2100) under the RCP4.5 scenario, and by 30% under the RCP8.5, suggesting that the frequency and extent of large wildfires will increase throughout the Mediterranean Basin. Wildfire is a complex phenomenon that occurs when three conditions are met: available fuel, an ignition source (due to lightning or human activities) and weather conditions conducive to fires (fire weather) 1. Climate and weather are important drivers of wildfire activity across a range of timescales 2-5 , and, consequently, current and potential future climate-induced changes in wildfire activity might threaten ecosystems and human well-being 6. In most Euro-Mediterranean countries, wildfire activity has been declining owing to management and suppression measures undertaken since the 1980s 7. However, some recent extreme wildfire events, including those that occurred in 2016 in France 8 , 2017 in Spain and Portugal 9 and 2018 in Greece 10 have highlighted the limits of wildfire suppression capabilities under exceptional fire-weather conditions. Furthermore, studies show that wildfire activity is expected to increase across the Mediterranean Basin due to climate change 11,12. However, how the combinations of climate and weather conditions that promote the largest wildfires will respond to climate change remain largely unknown. Climate and weather are both drivers of wildfire activity. Soil moisture deficit over days to months increases fuel aridity and flammability 6,13 while a number of synoptic weather conditions associated to different combinations of short-term and instantaneous meteorological fields (precipitation, temperature, relative humidity and wind speed) influence wildfire behaviour 5,14. Most of the largest wildfires occur when these conditions are met 8. For instance, the combination of extreme drought with extreme wind or heatwaves have both been identified as crucial factors in the occurrence of crown wildfires in Mediterranean forests and shrublands 15-17. In this study, we focus on the frequency of current and future weather and climate conditions associated with wildfires in four countries (France, Portugal, Greece, Tunisia) of the Mediterranean basin covering most of its diverse biogeographic and climatic conditions (Supplementary Figs. S1-S3). Building on the insights gained open

Published
2020

12. Impact des condition locales de sol et sou-sol sur le variabilité inter-individuelle de réponse à la sécheresse : apport de la tomographie de résistivité électrique

Author

Carrière, S. D., Ruffault, J., Pimont, F., Doussan, C., Simioni, G, CHALIKAKIS, Konstantinos, Limousin, J.-M, Scotti, I, Courdier, F, Cakpo, C.-B, Davi, H, Martin St-Paul, N. K., Environnement Méditerranéen et Modélisation des Agro-Hydrosystèmes (EMMAH), Avignon Université (AU)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Avignon Université (AU), Service National d'Observation sur le KARST (SNO Karst), Institut national des sciences de l'Univers (INSU - CNRS), Risques, Ecosystèmes, Vulnérabilité, Environnement, Résilience (RECOVER), Aix Marseille Université (AMU)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Institut National de la Recherche Agronomique (INRA), Unité de Recherches Forestières Méditerranéennes (URFM), Centre d’Ecologie Fonctionnelle et Evolutive (CEFE), Université Paul-Valéry - Montpellier 3 (UPVM)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Unité de recherche Plantes et Systèmes de Culture Horticoles (PSH), Université Paul-Valéry - Montpellier 3 (UM3)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-École pratique des hautes études (EPHE)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud])-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut de Recherche pour le Développement (IRD [France-Sud])-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE)-Université de Montpellier (UM)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Université Paul-Valéry - Montpellier 3 (UM3), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Aix Marseille Université (AMU), Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut National de la Recherche Agronomique (INRA)-Université Paul-Valéry - Montpellier 3 (UPVM)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), and Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut de Recherche pour le Développement (IRD [France-Sud])

Subjects
leaf traits, [SDV.EE]Life Sciences [q-bio]/Ecology, environment, Mediterranean forests, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], hydrogeophysics, tree water status, ERT, drought response, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, [SDE.BE]Environmental Sciences/Biodiversity and Ecology, [SDV.SA.SDS]Life Sciences [q-bio]/Agricultural sciences/Soil study, [SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology
Abstract

International audience; 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 resistivity (PVR) between dry and wet conditions as an indicator of spatial variability in total available water content. PVR was computed in two different depth ranges (0-2 and 2-5 m) for eleven Quercus ilex stools in a Mediterranean forest stand. PVR values were compared to biological traits, including tree water status (predawn water potential (Ψ)), leaf traits (δ 13 C, leaf mass area (LMA)), and canopy defoliation measured after intense drought.We found significant correlations between PVR and biological variables. For Ψ , the nature and strength of the correlations vary according to the level of drought intensity. The correlation between Ψ and PVR was positive during well-watered conditions in the upper layer (0-2 m) and during water-limited conditions in the deeper layer (2-5 m). During most severe droughts, however, the Ψ was negatively correlated with PVR in the upper layer. Trees with lower PVR in the upper layer were also associated with water use efficiency (higher δ 13 C), higher LMA, and a lower level of defoliation after extreme drought.Overall, our results indicate that local differences in soil/subsoil properties affect tree response to drought and suggest that less favorable soil/subsoil conditions (lower PVR) can lead to lower water stress during the driest period and to lower defoliation after extreme drought. Plausible explanations for this better acclimation include higher stomatal regulation and improved deep soil and subsoil water exploration by trees located in more adverse conditions. We encourage the development of ERT in ecological studies to further explore the interrelated relationships between soil/subsoil, climate, and tree functioning.

Published
2020

13. Modelling live fuel moisture content at leaf and canopy scale under extreme drought using a lumped plant hydraulic model

Author

Martin-StPaul, N, primary, Ruffault, J, additional, Blackmann, C, additional, Cochard, H, additional, De Cáceres, M, additional, Delzon, S, additional, Dupuy, JL, additional, Fargeon, H, additional, Lamarque, L, additional, Moreno, M, additional, Parsell, R, additional, Pimont, F, additional, Ourcival, JM, additional, Torres-Ruiz, J, additional, and Limousin, JM, additional

Published
2020
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16. Impact of local soil and subsoil conditions on inter-individual variations in tree responses to drought: insights from Electrical Resistivity Tomography

Author

Carrière, S.D., primary, Ruffault, J., additional, Pimont, F., additional, Doussan, C., additional, Simioni, G., additional, Chalikakis, K., additional, Limousin, J.-M., additional, Scotti, I., additional, Courdier, F., additional, Cakpo, C.-B., additional, Davi, H., additional, and Martin-StPaul, N.K., additional

Published
2020
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20. Les effets du changement climatique sur l'agriculture et la forêt en Provence-Alpes-Côte d'Azur

Author

Barbier, J.M., Baury, C., Bertuzzi, P., Bondeau, Alberte, Couderc, V., Courbet, F., Curt, T., Dalstein-Richier, L., Davi, H., Delmotte, S., Dobremez, L., Dupuy, J.L., Fader, M., Farnet Da Silva, Anne Marie, Ferreira, O., Fouant, T., Garcia de Cortazar Atauri, I., Garde, L., Gauquelin, Thierry, Hossard, L., Gouache, D., Gros, R, Guibal, F., Hammond, R., Jezequel, S., Ladier, J., Lefevre, F., Legave, J.M., Mouret, J.C., Napoleone, C., Pimont, F., Prévosto, B., Rigolot, Eric, Rossello, P., Sicard, P., Vennetier, M., Vial, B., Vieux, S., Institut méditerranéen de biodiversité et d'écologie marine et continentale (IMBE), Avignon Université (AU)-Aix Marseille Université (AMU)-Institut de recherche pour le développement [IRD] : UMR237-Centre National de la Recherche Scientifique (CNRS), Innovation et Développement dans l'Agriculture et l'Alimentation (UMR Innovation), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Risques, Ecosystèmes, Vulnérabilité, Environnement, Résilience (RECOVER), Aix Marseille Université (AMU)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Développement des territoires montagnards (UR DTGR), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Rossello, P., Centre National de la Recherche Scientifique (CNRS)-Institut de recherche pour le développement [IRD] : UMR237-Aix Marseille Université (AMU)-Avignon Université (AU), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Aix Marseille Université (AMU), and Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut National de la Recherche Agronomique (INRA)-Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)

Subjects
climatic change, CHANGEMENT CLIMATIQUE, [SDE]Environmental Sciences, FORET MEDITERRANEENNE, agriculture, mediterranean forest
Abstract

Ce cahier diffuse des connaissances scientifiques (non exhaustives) sur les effets du changement climatique sur l'agriculture et la forêt en Provence-Alpes-Côte d'Azur. Les cultures (vergers, céréales, riz, maraîchage...) et les forêts (feuillus, conifères) bénéficient des bienfaits du climat méditerranéen qui offre des conditions favorables au développement des plantes sous certaines conditions, mais souffrent aussi des événements extrêmes qui le ponctuent à intervalles irréguliers. Le climat méditerranéen qui sévit en région PACA pourrait se résumer par Toulourenc (« tout ou rien » en provençal), du nom du cours d'eau à caractère torrentiel qui coule dans la vallée étroite située au pied du versant nord du mont Ventoux. Avec le changement climatique actuel, les aspects négatifs de notre climat sont appelés à se renforcer et font déjà peser sur les terroirs agricoles et les forêts emblématiques de la région de nouvelles contraintes auxquelles il est nécessaire de faire face pour éviter des conséquences trop néfastes. Mais la pérennité et le développement des systèmes agricoles et forestiers ne dépendent pas seulement de l'évolution du climat. L'urbanisation, l'occupation des sols, les pollutions locales (sol, air, eau), les incendies, mais aussi les pratiques culturales et la gestion forestière, jouent un rôle fondamental. Il convient donc de privilégier une approche transversale. Cette publication souligne les conséquences du changement climatique sur l'agriculture et la forêt en prenant soin d'identifier les enjeux environnementaux, économiques et sociaux, les risques à l'échelle régionale et locale, mais aussi les solutions susceptibles de réduire les impacts (atténuation, adaptation) et les éventuelles opportunités à saisir. Comme dans le précédent cahier, la contribution des chercheurs et experts, exerçant leur métier en région PACA et dans les territoires limitrophes4, sous forme d'articles et de zooms, apporte des éléments de compréhension afin de mieux cerner les problématiques liées au changement climatique.

Published
2016

22. Simulation numérique du couplage surface/canopée lors de la propagation d'un feu de cime en forêt boréale

Author

Morvan, Dominique, Accary, Gilbert, MÉRADJI, Sofiane, FOUGERE, D., Pimont, F., Dupuy, J.L., Service irevues, irevues, and Association Française de Mécanique

Subjects
Feu de forêt, Combustion, [PHYS.MECA]Physics [physics]/Mechanics [physics], [PHYS.MECA] Physics [physics]/Mechanics [physics], modélisation
Abstract

Colloque avec actes et comité de lecture. Internationale.; International audience; Cette étude concerne la modélisation numérique de l'ignition et de la propagation d'un feu de cime dans une forêt de type boréale. La formulation mathématique est basée sur une approche multi-phasique, construite à partir des équations de conservation (masse, quantité de mouvement, énergie) gouvernant l'évolution du système couplé formé par la végétation et l'atmosphère ambiant. Le modèle a préalablement été testé à petite échelle, sur des feux de litière homogène et à plus grande échelle, sur des feux de prairie et en garrigue Méditerranéenne. Les résultats ont été comparés avec des données expérimentales de la littérature, et les prédictions des modèles empiriques opérationnels développés en Australie (MkV) et aux Etats Unis (BEHAVE). Le modèle a été étendu à un profil de végétation composé d'une couche arbustive et d'une canopée. Les résultats mettent en évidence le rôle joué par le combustible de surface sur la dynamique générale du feu de cime. Les résultats numériques ont été confrontés aux données collectées à l'occasion de campagnes expérimentales internationales réalisées au Canada.

Published
2007

28. Versitility of FIRETEC, a physics-based wildfire model

Author

Linn, R., primary, Winterkamp, J., additional, Canfield, J., additional, Sauer, J., additional, Colman, J., additional, Reisner, J., additional, Edminster, C., additional, Pimont, F., additional, Dupey, J., additional, and Cunningham, P., additional

Published
2006
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29. The effects of climate change on agriculture and forest in Provence-Alpes-Côte d'Azur Region

Author

Barbier, J. M., Baury, C., Bertuzzi, P., Alberte Bondeau, Couderc, V., Courbet, F., Curt, T., Dalstein-Richier, L., Davi, H., Delmotte, S., Dobremez, L., Dupuy, J. L., Fader, M., Anne Marie Farnet da Silva, Ferreira, O., Fouant, T., Iñaki Garcia de Cortazar-Atauri, Garde, L., Thierry Gauquelin, Hossard, L., Gouache, D., Gros, R., Guibal, F., Hammond, R., Jezequel, S., Ladier, J., Lefevre, F., Legave, J. M., Mouret, J. C., Napoleone, C., Pimont, F., Prévosto, B., Rigolot, E., Rossello, P., Sicard, P., Vennetier, M., Vial, B., and Vieux, S.

31. Isohydricity and hydraulic isolation explain reduced hydraulic failure risk in an experimental tree species mixture.

Author

Moreno M, Simioni G, Cochard H, Doussan C, Guillemot J, Decarsin R, Fernandez-Conradi P, Dupuy JL, Trueba S, Pimont F, Ruffault J, Jean F, Marloie O, and Martin-StPaul NK

Subjects
Plant Roots physiology, Plant Leaves physiology, Plant Transpiration physiology, Models, Biological, Species Specificity, Dehydration, Quercus physiology, Pinus physiology, Water metabolism, Trees physiology, Droughts, Plant Stomata physiology, Soil chemistry
Abstract

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 isohydric Aleppo pine (Pinus halepensis, drought avoidant) and the anisohydric holm oak (Quercus ilex, drought tolerant) affects tree water stress during extreme drought. Our experiment showed that the intimate mixture strongly alleviated Q. ilex water stress while it marginally impacted P. halepensis water stress. Three mechanistic explanations for this pattern are supported by our modeling analysis. First, the difference in stomatal regulation between species allowed Q. ilex trees to benefit from additional soil water in mixture, thereby maintaining higher water potentials and sustaining gas exchange. By contrast, P. halepensis exhibited earlier water stress and stomatal regulation. Second, P. halepensis trees showed stable water potential during drought, although soil water potential strongly decreased, even when grown in a mixture. Model simulations suggested that hydraulic isolation of the root from the soil associated with decreased leaf cuticular conductance was a plausible explanation for this pattern. Third, the higher predawn water potentials for a given soil water potential observed for Q. ilex in mixture can-according to model simulations-be explained by increased soil-to-root conductance, resulting from higher fine root length. This study brings insights into the mechanisms involved in improved drought resistance of mixed species forests., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Published
2024
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32. Plant hydraulics at the heart of plant, crops and ecosystem functions in the face of climate change.

Author

Torres-Ruiz JM, Cochard H, Delzon S, Boivin T, Burlett R, Cailleret M, Corso D, Delmas CEL, De Caceres M, Diaz-Espejo A, Fernández-Conradi P, Guillemot J, Lamarque LJ, Limousin JM, Mantova M, Mencuccini M, Morin X, Pimont F, De Dios VR, Ruffault J, Trueba S, and Martin-StPaul NK

Subjects
Water physiology, Soil, Crops, Agricultural, Droughts, Ecosystem, Climate Change
Abstract

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. Consequently, any variation in the hydraulic characteristics of plants is likely to significantly impact various mechanisms and processes related to plant growth, survival and production, as well as the risk of biotic attacks and forest fire behaviour. However, the integration of hydraulic traits into disciplines such as plant pathology, entomology, fire ecology or agriculture can be significantly improved. This review examines how plant hydraulics can provide new insights into our understanding of these processes, including modelling processes of vegetation dynamics, illuminating numerous perspectives for assessing the consequences of climate change on forest and agronomic systems, and addressing unanswered questions across multiple areas of knowledge., (© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation.)

Published
2024
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33. Integrating plant physiology into simulation of fire behavior and effects.

Author

Dickman LT, Jonko AK, Linn RR, Altintas I, Atchley AL, Bär A, Collins AD, Dupuy JL, Gallagher MR, Hiers JK, Hoffman CM, Hood SM, Hurteau MD, Jolly WM, Josephson A, Loudermilk EL, Ma W, Michaletz ST, Nolan RH, O'Brien JJ, Parsons RA, Partelli-Feltrin R, Pimont F, Resco de Dios V, Restaino J, Robbins ZJ, Sartor KA, Schultz-Fellenz E, Serbin SP, Sevanto S, Shuman JK, Sieg CH, Skowronski NS, Weise DR, Wright M, Xu C, Yebra M, and Younes N

Subjects
Plants, Plant Physiological Phenomena, Water, Carbon, Ecosystem, Fires, Wildfires
Abstract

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 representation of woody vegetation in fire models. Currently, the most advanced representations of fire behavior and biophysical fire effects are found in distinct classes of fine-scale models and do not capture variation in live fuel (i.e. living plant) properties. We demonstrate that plant water and carbon dynamics, which influence combustion and heat transfer into the plant and often dictate plant survival, provide the mechanistic linkage between fire behavior and effects. Our conceptual framework linking remotely sensed estimates of plant water and carbon to fine-scale models of fire behavior and effects could be a critical first step toward improving the fidelity of the coarse scale models that are now relied upon for global fire forecasting. This process-based approach will be essential to capturing the influence of physiological responses to drought and warming on live fuel conditions, strengthening the science needed to guide fire managers in an uncertain future., (© 2023 The Authors New Phytologist © 2023 New Phytologist Foundation.)

Published
2023
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34. Plant hydraulic modelling of leaf and canopy fuel moisture content reveals increasing vulnerability of a Mediterranean forest to wildfires under extreme drought.

Author

Ruffault J, Limousin JM, Pimont F, Dupuy JL, De Càceres M, Cochard H, Mouillot F, Blackman CJ, Torres-Ruiz JM, Parsons RA, Moreno M, Delzon S, Jansen S, Olioso A, Choat B, and Martin-StPaul N

Subjects
Forests, Trees physiology, Plant Leaves physiology, Water physiology, Droughts, Wildfires
Abstract

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 innovative process-based predictions of leaf live fuel moisture content (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 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., (© 2022 The Authors. New Phytologist © 2022 New Phytologist Foundation. This article has been contributed to by US Government employees and their work is in the public domain in the USA.)

Published
2023
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35. Prediction of regional wildfire activity in the probabilistic Bayesian framework of Firelihood.

Author

Pimont F, Fargeon H, Opitz T, Ruffault J, Barbero R, Martin-StPaul N, Rigolot E, RiviÉre M, and Dupuy JL

Subjects
Bayes Theorem, Ecosystem, Forests, Fires, Wildfires
Abstract

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-component, Bayesian, hierarchically structured, probabilistic model of daily fire activity, which is modeled as the outcome of a marked point process: individual fires are the points (occurrence component), and fire sizes are the marks (size component). The space-time Poisson model for occurrence is adjusted to gridded fire counts using the integrated nested Laplace approximation (INLA) combined with the stochastic partial differential equation (SPDE) approach. The size model is based on piecewise-estimated Pareto and generalized Pareto distributions, adjusted with INLA. The Fire Weather Index (FWI) and forest area are the main explanatory variables. Temporal and spatial residuals are included to improve the consistency of the relationship between weather and fire occurrence. The posterior distribution of the Bayesian model provided 1,000 replications of fire activity that were compared with observations at various temporal and spatial scales in Mediterranean France. The number of fires larger than 1 ha across the region was coarsely reproduced at the daily scale, and was more accurately predicted on a weekly basis or longer. The regional weekly total number of larger fires (10-100 ha) was predicted as well, but the accuracy degraded with size, as the model uncertainty increased with event rareness. Local predictions of fire numbers or burned areas also required a longer aggregation period to maintain model accuracy. The estimation of fires larger than 1 ha was also consistent with observations during the extreme fire season of the 2003 unprecedented heat wave, but the model systematically underrepresented large fires and burned areas, which suggests that the FWI does not consistently rate the actual danger of large fire occurrence during heat waves. Firelihood enabled a novel analysis of the stochasticity underlying fire hazard, and offers a variety of applications, including fire hazard predictions for management and projections in the context of climate change., (© 2021 by the Ecological Society of America.)

Published
2021
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36. Increased likelihood of heat-induced large wildfires in the Mediterranean Basin.

Author

Ruffault J, Curt T, Moron V, Trigo RM, Mouillot F, Koutsias N, Pimont F, Martin-StPaul N, Barbero R, Dupuy JL, Russo A, and Belhadj-Khedher C

Abstract

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 an increase in the frequency of two heat-induced fire-weather types that have been related to the largest wildfires in recent years. Heat-induced fire-weather types are characterized by compound dry and warm conditions occurring during summer heatwaves, either under moderate (heatwave type) or intense (hot drought type) drought. The frequency of heat-induced fire-weather is projected to increase by 14% by the end of the century (2071-2100) under the RCP4.5 scenario, and by 30% under the RCP8.5, suggesting that the frequency and extent of large wildfires will increase throughout the Mediterranean Basin.

Published
2020
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37. [Effects of fire recurrence on fire behaviour in cork oak woodlands (Quercus suber L.) and Mediterranean shrublands over the last fifty years].

Author

Schaffhauser A, Pimont F, Curt T, Cassagne N, Dupuy JL, and Tatoni T

Subjects
Ecosystem, France, Time Factors, Fires, Forests, Quercus
Abstract

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. The mosaic was dominated by Quercus suber L. and Erica-Cistus shrubland communities. We described the vegetation structure through measurements of tree height, base of tree crown or shrub layer, mean diameter, cover, plant water content and bulk density. We used the physical model Firetec to simulate the fire behaviour. Fire intensity, fire spread, plant water content and biomass loss varied significantly according to fire recurrence and vegetation structure, mainly linked to the time since the last fire, then the number of fires. These results confirm that past fire recurrence affects future fire behaviour, with multi-layered vegetation (particularly high shrublands) producing more intense fires, contrary to submature Quercus woodlands that have not burnt since 1959 and that are unlikely to reburn. Further simulations, with more vegetation scenes according to shrub and canopy covers, will complete this study in order to discuss the fire propagation risk in heterogeneous vegetation, particularly in the Mediterranean area, with a view to a local management of these ecosystems., (Copyright © 2015 Académie des sciences. Published by Elsevier SAS. All rights reserved.)

Published
2015
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