Extreme wildfire events are linked to global-change-type  droughts in the northern Mediterranean

Ruffault, Julien; Curt, Thomas; Martin‐StPaul, Nicolas; Moron, Vincent; Trigo, Ricardo M.

doi:10.5194/nhess-18-847-2018

Cited by 131 publications

(83 citation statements)

References 45 publications

(56 reference statements)

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“…One of the metric of water content or moisture content of plant is defined as the ratio of water mass to the dry mass. In the context of wildfire studies it is referred to as Live Fuel Moisture Content (LFMC), a variable that is is increasingly recognized as a critical factor in wildfire behavior (Rossa et al 2016;Pimont et al 2019a), hazard and activity (Dennison and Moritz 2009;Yebra et al 2013;Ruffault, Curt, et al 2018;Pimont et al 2019b). Furthermore, being strongly determined by drought conditions, LFMC is one of the factors that might be responsible for observed and projected increase in wildfire hazard because of the increase in the frequency of drought event due to climate change.…”

Section: Introductionmentioning

confidence: 99%

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

Martin‐StPaul¹,

Ruffault²,

Blackmann³

et al. 2020

Preprint

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Ø 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. Ø In this paper, we explore the functional and ecophysiological drivers of LFMC during drought at the leaf and canopy scale using the SurEau-Ecos model, and a three years dataset of leaf and canopy scale measurements on a mature Quercus ilex forest, including an extreme drought. The model is based on forest hydrology and plant hydraulics and allows to simulate temporal variations of water potential and content at a daily time step. At leaf level, it simulates the relationship between water potential and water content by separating the apoplasm and the symplasm. Symplasm water content is modeled using the pressure volume curve theory, and apoplasm water content is modelled using the xylem vulnerability to cavitation. Fuel moisture content was upscaled to the canopy level by accounting for foliage mortality estimated from drought induced cavitation. Ø The model was parameterized either with site-measured traits or using a calibration procedure, and compared with water potential and LFMC measured at leaf level, and NDVI variation measured at canopy level and taken as a surrogate for foliage mortality. Ø At leaf level, LFMC prediction using measured hydraulic traits could be improved by considering year-to-year osmotic adjustments. At canopy level, foliage mortality due to drought induced cavitation was a key driver of LFMC decline during the most extreme drought. Ø A sensitivity analysis showed that parameters driving soil water balance (leaf area index, soil water capacity, and regulation of transpiration) and parameters determining pressure volume curves are key traits driving LFMC dynamics at leaf level. At the canopy level, parameters that drives hydraulic failure were the most sensitive and included, both soil water balance parameters and hydraulic traits (the leaf vulnerability to cavitation) were the main drivers of LFMC decline during extreme drought. Ø We also showed that under normal historic weather conditions, most variation of LFMC are linked to reversible symplasm dehydration, however under future, hotter and dryer conditions, most variations are due to the decline canopy of LFMC driven by foliage mortality.

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Section: Introductionmentioning

confidence: 99%

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

Martin‐StPaul¹,

Ruffault²,

Blackmann³

et al. 2020

Preprint

View full text Add to dashboard Cite

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“…For instance, high severity wildfires after drought has been shown to impede Calluna regeneration and facilitate dominance of pioneer bryophytes in British blanket bogs (Maltby et al, 1990;Legg et al, 1992). Altered fire regimes associated with climatic and environmental change (Kasischke and Turetsky, 2006;Albertson et al, 2010;Bowman et al, 2011;Moritz et al, 2012;Pausas and Keeley, 2014;Ruffault et al, 2018), including higher severity wildfires because of projected drier summers (Dai, 2013;Cook et al, 2014), may therefore impact on post-fire trajectories and rates of plant community change (Wang and Kemball, 2005;Kettridge et al, 2015). In the UK, extreme wildfire activity and severity following the prolonged summer drought of 2018 has brought the need to better understand the effects of high severity fires on Calluna-dominated habitats into sharp focus (Anon, 2018).…”

Section: Introductionmentioning

confidence: 99%

Increased fire severity alters initial vegetation regeneration across Calluna-dominated ecosystems

Grau‐Andrés

Davies

Waldron

et al. 2019

Journal of Environmental Management

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Calluna vulgaris-dominated habitats are valued for ecosystem services such as carbon storage and for their conservation importance. Climate and environmental change are altering their fire regimes. In particular, more frequent summer droughts will result in higher severity wildfires. This could alter the plant community composition of Calluna habitats and thereby influence ecosystem function. To study the effect of fire severity on community composition we used rain-out shelters to simulate drought prior to experimental burns at two Callunadominated sites, a raised bog and a heathland. We analysed species abundance in plots surveyed ca. 16 months after fire in relation to burn severity (indicated by fire-induced soil heating). We found that fire severity was an important control on community composition at both sites. Higher fire severity increased the abundance of ericoids, graminoids and acrocarpous mosses, and decreased the abundance of pleurocarpous mosses compared to lower severity fires. At the raised bog, the keystone species Sphagnum capillifolium and Eriophorum vaginatum showed no difference in regeneration with fire severity. Species and plant functional type beta-diversity increased following fire, and was similar in higher compared to lower severity burns. Our results further our understanding of the response of Calluna-dominated habitats to projected changes in fire regimes, and can assist land managers using prescribed fires in selecting burning conditions to achieve management objectives. CAVU = Calluna vulgaris, CECO = Cephalozia connivens, CL.sp = Cladonia spp., DEFL = Deschampsia flexuosa, DISC = Dicranum scoparium, Duff = Duff, ERCI = Erica cinerea, ERVA = Eriophorum vaginatum, HYJU = Hypnum jutlandicum, HYSP = Hylocomium splendens, Litter = Litter, LOBI = Lophocolea bidentata, ODSP = Odontoschisma sphagni, PLSH = Pleurozium schreberi, PLUN = Plagiothecium undulatum, POER = Potentilla erecta, POJU = Polytrichum juniperinum, RHSQ = Rhytidiadelphus squarrosus, SPCA = Sphagnum capillifolium, VAVI = Vaccinium vitis-idaea.

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“…Hence, the final BA depends upon the balance between environmental and socioeconomic drivers that favor fire enlargement (remote terrain, strong wind, connectivity, and management of fuels and landscapes by humans; see Fernandes et al, 2016) and the efficacy of suppression tactics (Lahaye et al, 2014). For many geophysical variables and/or hazards such as rainfall, snowfall, or river discharge, protective measures are designed to withstand an event with a given small exceedance probability, i.e., an event that is generally much rarer than those already observed (Sharma et al, 2012). As a consequence, a robust evaluation of the return period of these extreme events is of the utmost importance to risk mitigation (Read and Vogel, 2015;Volpi et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Has fire policy decreased the return period of the largest wildfire events in France? A Bayesian assessment based on extreme value theory

Evin¹,

Curt

Eckert³

2018

Nat. Hazards Earth Syst. Sci.

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Very large wildfires have high human, economic, and ecological impacts so that robust evaluation of their return period is crucial. Preventing such events is a major objective of the new fire policy set up in France in 1994, which is oriented towards fast and massive fire suppression. Whereas this policy is probably efficient for reducing the mean burned area (BA), its effect on the largest fires is still unknown. In this study, we make use of statistical extreme value theory (EVT) to compute return periods of very large BAs in southern France, for two distinct periods (1973 to 1994 and 1995 to 2016) and for three pyroclimatic regions characterized by specific fire activities. Bayesian inference and related predictive simulations are used to fairly evaluate related uncertainties. Results demonstrate that the BA corresponding to a return period of 5 years has actually significantly decreased, but that this is not the case for large return periods (e.g., 50 years). For example, in the most fire-prone region, which includes Corsica and Provence, the median 5year return level decreased from 5000 to 2400 ha, while the median 50-year return level decreased only from 17 800 to 12 500 ha. This finding is coherent with the recent occurrence of conflagrations of large and intense fires clearly far beyond the suppression capacity of firemen. These fires may belong to a new generation of fires promoted by long-term fuel accumulation, urbanization into the wildland, and ongoing climate change. These findings may help adapt the operational system of fire prevention and suppression to ongoing changes. Also, the proposed methodology may be useful for other case studies worldwide.Published by Copernicus Publications on behalf of the European Geosciences Union.

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Extreme wildfire events are linked to global-change-type droughts in the northern Mediterranean

Cited by 131 publications

References 45 publications

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

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

Increased fire severity alters initial vegetation regeneration across Calluna-dominated ecosystems

Has fire policy decreased the return period of the largest wildfire events in France? A Bayesian assessment based on extreme value theory

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