Fire Size Research Articles

Experimental study on thermal stratification characteristics in tunnel fires under the effect of canyon cross wind

In order to investigate the thermal stratification characteristics induced by pool fire and canyon cross wind, a set of tests were carried out in a 1:20 model tunnel. Experimental parameters were the canyon wind speed, longitudinal fire location and fire size. Results show that the dimensionless smoke layer thickness h∗ (the ratio of smoke layer thickness to hydraulic diameter) downstream the fire generally increases with increasing canyon wind speed until reaching the maximum value, and h∗ of a smaller-scale fire is slightly greater than that of a larger-scale fire at most canyon wind speeds. However, h∗ value upstream the fire is almost between 0.2 and 0.3 (h∗ = 0 is not considered). The smoke stratification downstream the fire gradually worsens with increasing canyon wind speed and decreasing distance between the fire source and the upstream portal Df in the cases of 0.194 ≤ Df∗ < 1 (Df∗ represents the ratio of Df to the tunnel length), while the smoke stratification upstream the fire is always obvious unless there is no smoke. As Df increases, the critical Froude number for judging the smoke stratification status decreases first for 0 ≤ Df∗ < 0.028 and then increases for 0.028 ≤ Df∗ < 0.306, and tends to be a constant value for 0.306 ≤ Df∗ < 1.

Performance of steel moment-resisting frames in post-earthquake horizontally traveling fire

PurposeThe study investigates the performance of a three-story unprotected steel moment-resisting frame (SMRF) designed for high seismic demand in the fire-only (FO) and post-earthquake uniform and traveling fires (PEF). The primary objective is to investigate the effects of seismic residual deformation on the structure's performance in horizontally traveling fires. The traveling fire methodology, unlike conventional fire models, considers a spatially varying temperature environment.Design/methodology/approachMulti-step finite element simulations were carried out on undamaged and damaged frames to provide insight into the effects of the earthquake-initiated fires on the local and global behavior of SMRF. The earthquake simulations were conducted using nonlinear time history analysis, whereas the structure in the fire was investigated by sequential thermal-structural analysis procedure in ABAQUS. The frame was subjected to a suite of seven ground motions. In total, four horizontal traveling fire sizes were considered along with the Eurocode (EC) parametric fire for a comparison. The deformation history, axial force and moment variation in the critical beams and columns of affected compartments in the fire heating and cooling regimes were examined. The global structural performance in terms of inter-story drifts in FO and PEF scenarios was investigated.FindingsIt was observed that the larger traveling fires (25 and 48%) are more detrimental to the case study frame than the uniform EC parametric fire. Besides, no appreciable difference was observed in time and modes of failure of the structure in FO and PEF scenarios within the study's parameters.Originality/valueThe present study considers improved traveling fire methodology as an alternate design fire for the first time for the PEF performance of SMRF. The analysis results add to the much needed database on structures' performance in a wide range of fire scenarios.

Experimental study on temperature profile in long-narrow compartment fire with multiple lateral openings

The openings of a compartment under fire condition are very important to exhaust the hot smoke. However, the related impacts on the indoor environment are still not clear so far to guide future designs. Experiments were then conducted using a model long-narrow compartment with multiple lateral openings. The temperature inside the compartment and the temperature profile underneath the ceiling were investigated and compared with the predict ions of those previous models. Experimental results show that the lateral opening conditions mainly affect the temperature near the fire source, and this effect does not follow a single pattern with the change of the number of lateral openings. Keeping the openings near the fire source closed and symmetrically opening the openings away from the fire source can expand the fire hazard, while asymmetrically opening the openings on the side of the fire source can effectively reduce the temperature caused by the fire. The classic models for predicting the maximum temperature rise based on the confined space with open ends underestimate the experimental data in this work. An empirical model considering various fire sizes was developed to predict the temperature decay profile underneath the ceiling. The critical dimensionless distance and the attenuation index of the attenuation zone are both related to the convective heat release rate, showing power and linear functions, respectively. These findings and results can provide reference for the fire risk assessment of a long-narrow compartment with multiple lateral openings.

Forest Management of Pinus pinaster Ait. in Unbalanced Forest Structures Arising from Disturbances—A Framework Proposal of Decision Support Systems (DSS)

Forests assume a great socioeconomic and environmental importance, requiring good management decisions to value and care for these natural resources. In Portugal, forest land use accounts for 34.5% of the continental area. The softwood species with the highest representation is maritime pine (Pinus pinaster Ait.). Traditionally, the species is managed as pure and even-aged stands for timber production, with a rotation age of 45 to 50 years. Depending on the initial stand density, the stands are thinned 2 to 4 times during the rotation period. Disturbances associated with forest fires have a negative impact on the age structure of stands over time, as they result in a narrow range of stand ages. This age homogenization over large forest areas increases with the recurrence and size of forest fires, bringing new challenges to forest management, namely the difficulty in ensuring the long-term sustainability of the wood supply. The problem aggravates with the increasing demand pressure on pine wood. This article aims to suggest a framework of DSS for Pinus pinaster that can effectively support the management of forest areas under these circumstances, i.e., narrow age ranges and high demand of harvested timber volume. A communal woodland area in the Northern region of Portugal affected by forest fires was selected as a study case. The Modispinaster model was used as the basis of the DSS, to simulate growth scenarios and interventions along the optional rotation period. Two clear-cut ages were considered: 25 and 40 years. The results obtained were the input data for an integer linear programming (ILP) model to obtain the plan that maximizes the volume of timber harvested in the study area, during the planning horizon. The ILP model has constraints bounding the area of clearings, and sustainability, operational and forestry restrictions. The computational results are a powerful tool for guidance in the decision-making of scheduling and forecasting the execution of interventions determining the set of stands that are exploited according to the different scenarios and the period in which the clear-cut is made throughout the planning horizon. Considering all constraints, the solution allows a balanced extraction of a total of 685 m3·ha−1, over the 50-year horizon, as well as the representation of all age classes at the end of the planning period.

Forest connectivity percolation thresholds for fire spread under different weather conditions

How fuel influences fire spread at different spatial scales has been broadly studied but it is still under research. Although prior research has generally explored fuel effects at the stand scale, there is increasing recognition that forest structure and composition at the landscape scale can regulate fire size when weather conditions allow fire to have enough initial capacity to spread. Simulation models have usually been adopted to test forest landscape structure’s effect on fire activity, but we still lack empirical evidence of these effects on a broad scale and using multiple fires. In this study, we use the graph theory and the percolation theory to test the relationship between forest functional connectivity and fire size in a Mediterranean region (Catalonia, NE Spain, ~32000 km2) and under different weather conditions. Using a total sample of 554 fires that occurred between 1987 and 2019, we relate fire size with forest connectivity inside the fire perimeter, which we describe with different interpretations of forest-land cover maps and at different fire dispersal distances (10-, 100- and 2000- meters spotting capacity). Previously, fires were classified according to the weather and drought conditions in which they occurred (windy, arid or regular days, and dry or non-dry conditions) with the hypothesis that the capacity of fire to “read” the forest landscape differs according to weather variables. We found that a forest percolation threshold existed for most types of fires: forest connectivity had a positive influence on fire size until a threshold at which the landscape becomes continuous and other processes to control fire cease to have effect. This percolation threshold is about 0.40 for fires occurring under arid conditions. Under regular weather conditions, the threshold is non-existent and forest connectivity always exerts a positive effect on fire size. Notably, forest connectivity has no influence on fire size on windy- and dry-weather days. All these results are of paramount relevance for forest and landscape management aimed at reducing wildfire risk, since for fires driven by extreme weather conditions (more prone to happen in the future), landscape offers less opportunities to stop them. Researchers and managers need to identify the probability of experiencing each of the different weather types in a climate change context to boost the management of forests and landscapes in a cost-effective way.

Rainfall-Linked Megafires as Innate Fire Regime Elements in Arid Australian Spinifex (Triodia spp.) Grasslands

Large, high-severity wildfires, or “megafires,” occur periodically in arid Australian spinifex (Triodia spp.) grasslands after high rainfall periods that trigger fuel accumulation. Proponents of the patch-burn mosaic (PBM) hypothesis suggest that these fires are unprecedented in the modern era and were formerly constrained by Aboriginal patch burning that kept landscape fuel levels low. This assumption deserves scrutiny, as evidence from fire-prone systems globally indicates that weather factors are the primary determinant behind megafire incidence, and that fuel management does not mitigate such fires during periods of climatic extreme. We reviewed explorer’s diaries, anthropologist’s reports, and remotely sensed data from the Australian Western Desert for evidence of large rainfall-linked fires during the pre-contact period when traditional Aboriginal patch burning was still being practiced. We used only observations that contained empiric estimates of fire sizes. Concurrently, we employed remote rainfall data and the Oceanic Niño Index to relate fire size to likely seasonal conditions at the time the observations were made. Numerous records were found of small fires during periods of average and below-average rainfall conditions, but no evidence of large-scale fires during these times. By contrast, there was strong evidence of large-scale wildfires during a high-rainfall period in the early 1870s, some of which are estimated to have burnt areas up to 700,000 ha. Our literature review also identified several Western Desert Aboriginal mythologies that refer to large-scale conflagrations. As oral traditions sometimes corroborate historic events, these myths may add further evidence that large fires are an inherent feature of spinifex grassland fire regimes. Overall, the results suggest that, contrary to predictions of the PBM hypothesis, traditional Aboriginal burning did not modulate spinifex fire size during periods of extreme-high arid zone rainfall. The mechanism behind this is that plant assemblages in seral spinifex vegetation comprise highly flammable non-spinifex tussock grasses that rapidly accumulate high fuel loads under favorable precipitation conditions. Our finding that fuel management does not prevent megafires under extreme conditions in arid Australia has parallels with the primacy of climatic factors as drivers of megafires in the forests of temperate Australia.

Putting fire on the map of Brazilian savanna ecoregions

The Brazilian savanna (Cerrado) is considered the most floristically diverse savanna in the world, home to more than seven thousand species. The region is a mosaic of savannas, grasslands and forests whose unique biophysical and landscape attributes are on the basis of a recent ecoregional map, paving the way to improved region-based strategies for land management actions. However, as a fire-prone ecosystem, Cerrado owes much of its distribution and ecological properties to the fire regime and contributes to an important parcel of South America burned area. Accordingly, any attempt to use ecoregion geography as a guide for management strategies should take fire into account, as an essential variable. The main aim of this study is to complement the ecoregional map of the Cerrado with information related to the fire component. Using remotely sensed information, we identify patterns and trends of fire frequency, intensity, seasonality, extent and scar size, and combine this information for each ecoregion, relying on a simple classification that summarizes the main fire characteristics over the last two decades. Results show a marked north-south fire activity gradient, with increased contributions from MATOPIBA, the latest agricultural frontier. Five ecoregions alone account for two thirds of yearly burned area. More intense fires are found in the Arc of Deforestation and eastern ecoregions, while ecoregions in MATOPIBA display decreasing fire intensity. An innovative analysis of fire scars stratified by size class shows that infrequent large fires are responsible for the majority of burned area. These large fires display positive trends over many ecoregions, whereas smaller fires, albeit more frequent, have been decreasing in number. The final fire classification scheme shows well defined spatially-aggregated groups, where trends are found to be the key factor to evaluate fire within their regional contexts. Results presented here provide new insights to improve fire management strategies under a changing climate.

Numerical Simulation of Converter Station Fire: A Study focus on the Fire Hazard of Valve Tower

The fire hazard of a valve tower in converter station fires were investigated by using the Fire Dynamics Simulator (FDS). The 2 m2, 5 m2 and 10 m2 transformer oil pool fires with the calculated heat release rate (HRR) of 2.02, 6.23 and 13.78 MW were considered in the simulations, and the smoke propagation process, smoke temperature and visibility were mainly concerned. The results showed that the whole valve tower was immersed in the fire smoke at about 600 s in 2 m2 fire condition, and the maximum temperature rise inside the valve hall was about 20ºC. In the 5 m2 fire condition, the smoke layer height descended to the bottom of the valve tower at about 300 s, and the visibility around the valve modules was lower than 5 m at about 450 s. The maximum smoke temperature inside the valve hall was over 60ºC, and the temperature of smoke around the valve modules ranged from 43 to 52ºC. In the 10 m2 fire condition, the valve tower was immersed in the fire smoke at about 210 s, and the visibility around the valve modules was lower than 5 m at about 300 s. The smoke temperature beneath the ceiling of the valve hall was over 100ºC, and the temperature at the height of valve towers ranged from 65 to 80ºC. It was observed that the larger the fire size was, the higher the fire hazard of the valve tower would be found. In the 5 m2 and 10 m2 pool fire conditions, the thermal damage to the valve tower was non-negligible. The normal operation of the electrical components in the valve tower might be affected, and the failure of electrical components might be occurred.

Simulation Study on the Influence of Fire Partition on Curtain Wall Temperature in Super High-Rise Buildings in China

The poor fire resistance characteristic of super high-rise curtain wall makes the curtain wall design one of the main approaches to improve its capacity for prevention and control over fire and smoke spread. The propagation of smoke leads to the increase in the temperature of the curtain wall on the upper and lower floors of the fire floor and consequently leads to glass fracture and other serious consequences. Current codes have control over fire resistance performance and size of fire partition materials but do not include requirements on the position of curtain walls on floors. By changing the position of fire partition in curtain walls, the paper carries out three comparative simulation experiments on two forms of fire partition: spandrel and fire prevention cornice. Besides, PyroSim is used to calculate the comparative simulation of fire and smoke spread and obtain the data on temperature variation nephogram and monitoring points in the center line of glass curtain walls during different fire scenarios, so as to discuss the influence of different positions of spandrels and fire canopy on fire hazard and smoke. This study finds out the following: fire canopy can better prevent the longitudinal spread of fire smoke than spandrels. The fire canopy above spandrels can reduce the flue-gas temperature. The higher the spandrels above floors, the faster the temperature of the central lines of glass curtain walls above fire floors reduced. However, the higher the spandrels above floors, the more uneven the distributions of high-temperature regions and low-temperature regions, thus leading to the increase in horizontal temperature differences of glass panels. This research conclusion can be taken as a reference for fire protection design of super high-rise glass curtain wall.

Investigation into the Lithium-Ion Battery Fire Resistance Testing Procedure for Commercial Use

Lithium-ion batteries (LIBs) have many advantages (e.g., high voltage and long-life cycle) in comparison to other energy storage technologies (e.g., lead acid), resulting in their applicability in a wide variety of structures. Simultaneously, the thermal stability of LIBs is relatively poor and can be damaged by exposure to fire. This paper presents an investigation into a fire resistance safety test for LIBs and the use of thermal sensors to evaluate exposure conditions and estimate the temperatures to which cells are subjected. Temperature distribution data and statistical analysis show significant differences of over 200 ∘C, indicating the stochastic nature of the heating curve despite following the testing procedure requirements. We concluded that the current testing procedure is inadequate for the reliable testing of LIBs, leaving an alarming loophole in the fire safety evaluation. The observed instability is mostly related to wind speed and direction, and fire source size.

Cover-based allometric estimate of aboveground biomass of a non-native, invasive annual grass (Bromus tectorum L.) in the Great Basin, USA

Cheatgrass (Bromus tectorum L.) presence in the Great Basin is associated with an increase in fire frequency and size, likely due to increased spatial continuity of fine fuel biomass. Measurements of the extent and cover of cheatgrass are steadily improving, but the strength of the relationship between cover and aboveground biomass (AGB) is unclear. An allometric equation that can reliably convert cover to AGB of cheatgrass would allow for improved incorporation of regional estimates of cover into models of fire activity, carbon storage, and net primary productivity, all of which rely on biomass. We measured cover and AGB of cheatgrass at 60 locations in the north-central Great Basin and used these measurements to model the relationship. We found a strong, linear relationship between the percent cover and AGB, which was improved after square root transformation of both cover and AGB, and after incorporating the number of days after peak NDVI that the biomass and cover were measured. These results show that AGB of cheatgrass can be reliably estimated from cover. It is likely that allometric equations based on cover will be effective for other grass species, but care must be taken to account for phenology (e.g., peak NDVI) in the estimation.

Modeling the duration and size of wildfires using joint mixture models

AbstractFire duration and fire size are key outcomes for quantifying the survivorship of extended attack fires, here considered to be fires with duration greater than 2 days and size greater than 4 ha. Past studies suggest that these key outcomes are correlated. As well, fire behavior, linked to hidden effects, tends to yield that fires arise from different subpopulations. Indeed, it is not unusual for fire behavior to be identified as arising from normal or extreme subpopulations, for example. Here, we embed these two concepts into a new framework for jointly modeling fire duration and fire size. We develop a bivariate finite mixture framework that can be used to model duration and size with four subpopulations of the outcomes whereby duration and size are either normal or extreme. We utilize a shared random effect model as well as a bivariate Gaussian mixture model for such mixture modeling. We also incorporate the effect of explanatory variables associated with each fire event, on the posterior probability of the component that the fire belongs to, through a Dirichlet model. In an analysis of fire outcomes from British Columbia, Canada, we find that the majority of the fires are of normal or extreme magnitude in both outcomes, with strong evidence indicating correlation between duration and size. The effect of fire center, month, and several environmental covariates are identified as key predictors and we are able to determine through these approaches how these covariates differentially affect the four subpopulations.

Contrasting the role of human- and lightning-caused wildfires on future fire regimes on a Central Oregon landscape

Climate change is expected to increase fire activity in many regions of the globe, but the relative role of human vs. lightning-caused ignitions on future fire regimes is unclear. We developed statistical models that account for the spatiotemporal ignition patterns by cause in the eastern slopes of the Cascades in Oregon, USA. Projected changes in energy release component from a suite of climate models were used with our model to quantify changes in frequency and extent of human and lightning-caused fires and record-breaking events based on sizes of individual fires between contemporary (2006 −2015) and mid-century conditions (2031–2060). No significant change was projected for the number of human-caused fire ignitions, but we projected a 14% reduction in lightning-caused ignitions under future conditions. Mean fire sizes were 31% and 22% larger under future conditions (2031–2060) for human and lightning-caused ignitions, respectively. All but one climate model projected increased frequency of record-breaking events relative to the contemporary period, with the largest future fires being about twice the size of those of the contemporary period. This work contributes to understanding the role of lightning- and human-caused fires on future fire regimes and can help inform successful adaptation strategies in this landscape.

Analysis of the Fickle Fires in Global Regions

Forest fires occur in a wide range with distinctive fire elements, including fire size, expansion, speed and duration. To investigate when and where fire occurs in recent years and how the four factors differ in various regions, we here to analyse the chronological and terrestrial distribution of these fires, seeing the tendency to change four main fire elements. We focus on fourteen regions, including BONA (Boreal North America), TENA (Temperate North America), CEAM (Central America), NHSA (Northern Hemisphere South America), SHSA (Southern Hemisphere South America), EURO (Europe), MIDE (Middle East), NHAF (Northern Hemisphere Africa), SHAF (Southern Hemisphere Africa), CEAS (Central Asia), SEAS (Southeast Asia), EQAS (Equatorial Asia), AUST (Australia and New Zealand), BOAS (Boreal Asia. We finally conclude that the high level of precipitation, decrease in vegetation coverage and human intervention account for the decreasing fires in NHAF, SHAF, CEAS, NHSA. We also confirm that the increasing fires in BONA, TENA and MIDE are because of the rising temperature globally or more specifically, in these areas.

Study on the longitudinal ceiling temperature distribution induced by double pool fires in a tunnel

This paper investigated ceiling temperature profile induced by double pool fires in a tunnel. A series of small-scale experiments and fire dynamics numerical simulations have been carried out with different fire sizes and fire spacing. The results showed that the longitudinal ceiling temperature distribution falls into exponential decays, and the experimental data is higher than Delichatsios's model. Based on this, a new correction is proposed by introducing fire size and fire spacing to predict the longitudinal ceiling temperature decay. The proposed model can provide well prediction to present work and previous related data.

Area burned adjustments to historical wildland fires in Canada

Prior to delineation of fire perimeters from airborne and satellite imagery, fire management agencies in Canada employed conventional methods to map area burned based on sketch mapping, digitization from a global positioning system unit, and point buffering from geographic coordinates. These techniques usually provide a less precise representation of a wildland fire’s size and shape than those derived from image data. The aim of this study is to assess the discrepancy in fire size from these techniques that contribute to uncertainty in area burned. We paired independently generated fire perimeters derived from Landsat satellite imagery with conventional perimeters (n = 2792; mean area difference per fire = 40.1%), and developed a set of prediction models to estimate a Landsat area burned from conventional perimeters by considering the mapping source, method, agency, and time period. A two-fold cross validation predicting the logarithm of area burned from the models, indicated an R 2 = 0.95 (MAE = 0.10 ha; RMSE = 0.19 ha). From this, we created an adjusted area burned time series from 1950 to 2018 using the model-predicted estimates from conventional perimeters (75% of agency-reported area) in combination with unchanged estimates from agency perimeters derived from airborne and satellite imagery (13% of fires). The predicted estimates reduced the size of individual fires over 2000 ha on average in some years, contributing to an annual average reduction of approximately 11% of the area burned reported in the national agency fire database. By retrospectively applying a robust statistical adjustment to the fire size data, the historical overestimation in annual area burned—up to 1.4 Mha in a single year—could be substantially minimized.

What shapes fire size and spread in African savannahs?

AbstractFires play an important role in savannah ecosystems, shaping among other things vegetation structure and altering species composition. As direct and indirect anthropogenic pressures on these ecosystems increase, fire dynamics in savannahs are expected to change in the coming decades, with potential impacts on ecosystem functioning. Although the ecological impacts of fires are relatively well‐known, the factors that shape fire dynamics in these ecosystems have received less research attention. Using Pendjari National Park (Benin) as a case study, we assessed the importance of different biotic and abiotic factors in shaping fire size and spread in the region. Our results show that fires spread faster (1) in the middle of the dry season compared to the early or late dry season, (2) in areas that are far away from natural and anthropogenic firebreaks, and (3) in areas that are covered with highly flammable vegetation. By contrast, most vegetation types had little influence on fire size, which seems to depend instead on rainfall. Our approach and results highlight new avenues for satellite data to improve our understanding of fire dynamics in large, remote savannah ecosystems and to improve our ability to predict how fires spread, a key variable for wildlife management in the face of rapidly changing environmental conditions.

Research on Mountain Fire Detection method of UAV based on Mathematical Modeling method

For the first question, we establish two main models for SSA drones and repeater drones respectively. For repeater drones, we establish a grid search model, aiming at terrain, repeater range limits and other restrictions, by gradually removing the grid points, work out the optimal position and quantity of the repeater drones. For SSA drones, we also use the grid search model, considering the flight parameters of SAA drones, to find the position of the charging station (EOC) and fully meet the charging needs of SSA drones. Considering the impact of the size of fire, we divide the size of the fire into three levels, which correspond to different SSA drones demand quantities, and referred to the VRPTW algorithm to solve the TSP problem with different node requirements. Finally, we use genetic algorithm to optimize.

Human-climate interactions shape fire regimes in the Cerrado of São Paulo state, Brazil

The Cerrado is the most diverse tropical savanna in the world. As a fire-prone ecosystem, natural fire in the Cerrado shapes plant communities and drives evolutionary processes. Human activities and landscape management can alter natural fire regimes and reshape Cerrado dynamics, making biodiversity conservation a challenge, particularly in densely populated areas. We reconstructed the historical fire regime of three protected areas (PA) and their buffer zones in São Paulo state to understand how current fire exclusion policies are affecting fire regimes and to measure how human-climate-fire relationships can change in areas under different land management. We used Landsat satellite imagery, from 1984 to 2017, with 30 m of spatial resolution and 16 days of temporal resolution. In total, we mapped 49,471 ha of burned area, and we detected variations in fire frequency and fire size among sites. PA dominated by open savanna in Itirapina concentrated 93 % of all observed fires, while PA dominated by forest-like formations in Assis represented only 2% of the fires. Annual rainfall showed a very weak relationship (R2 = 0.04) with annual total burned area, while the rainfall split between dry and wet seasons showed a tendency to have a fuel moisture effect which determined the vegetation available to burn in the dry season (R² = 0.09). Fire regimes in PA were similar to those observed in buffer zones suggesting that fire-exclusion policies do not effectively prevent fires in PA that are surrounded by an anthropic matrix where fire is often used. When we included human factors in addition to rainfall, our models explained 44 % of variation of burned areas. We conclude that fire regimes in São Paulo Cerrado have been modified by humans and that fire exclusion is not a suitable policy for protected areas in this fire-prone ecosystem.

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

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 1ha 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 (10-100ha) 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 1ha 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.