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Three main research topics are reported in this dissertation. This research project focused on estimating the burden of injury on large federal wildland fires and describing the injury characteristics and risk factors for severity of injury in a sample of injured federal wildland firefighters. Chapter 2 "Peak incident management level affects rates of injury on large federal wildland fires" reports estimates of rates of injury for large federal wildland fires and assesses the effect of peak incident management level (PIML) as a predictor of rate of injury. After adjusting for seasonal factors and fire characteristics, PIML was a predictor of both rate of injury and odds of any injury occurrence, but the effect was opposite. Fires with higher PIML demonstrated lower incidence rate ratios, but the odds of injury were increased. Chapter 3 "Wildland fire job assignment and burden of injury" describes the injury characteristics and severity associated with the firefighter's job assignment in fire-related injuries reported to the United States Department of Interior. Job assignment was significantly associated with cause and nature of injury, but not with the severity of injury as defined by days off work or job transfer. Chapter 4 "Cause, characteristics and severity of injuries in wildland firefighters" examines the relationship between the cause of injury and type of injury and the severity of injury. Injuries caused by slips, trips or falls were most frequently reported. Injuries caused by bites or stings and plants were less likely to be severe relative to injuries caused by slips, trips or falls. Together, these studies provide evidence that injuries may significantly impact the wildland fire community, but that better information is needed to fully evaluate risk factors and develop evidence-based interventions.

Wildland fire is a natural part of the earth’s phenomenological pattern and like most natural phenomena has presented a challenge to human activity and engineering science. Wildfire presents Fire Safety Engineering with the task of developing fundamental research and designing analysis tools to address fire on a scale where interactions with atmospheric and terrestrial conditions dominate fire behavior. The research work presented in this thesis addresses a fundamental research issue involving transport processes in porous wildland fuel beds. This research project had the specific goal of developing an understanding of how transport processes affected the combustion of wildland fuels that were in the form of a porous bed. No detailed study could be found in the literature that specifically addressed how the fuel structure affected the combustion process in these types of fuels. To this end, a series of experiments were designed and carried out that approached the understanding of this problem using commonly available fire testing equipment, specifically the cone calorimeter and the FM Global Fire Propagation Apparatus. The goal of this research study and the basis for the novel and relevant contribution to the field of engineering was to conduct an experimental test series, analyze the data and examine the scalability of the results, to determine the effect of transport processes on the Heat Release Rate (HRR) of porous wildland fuels. The project concluded that flow dominates HRR in fires involving the wildland fuels tested. A dimensionless analysis of the fuel sample baskets showed consistency with well established mass transfer, fluid flow and chemical kinetic relationships. The dimensionless analysis also indicates that the experimental results should be scalable to similar configurations in larger fuel beds. One conclusion of this study was that wildland fire modeling efforts should invest in understanding flow conditions in fuel beds because this behavior dominates over the chemical kinetics of combustion for predicting HRR which is an important parameter in fire modeling.

Wildland fires are a type of vegetation fire that burn in a rural or wild landscape and affect many countries worldwide. They are an important mechanism in ecosystem maintenance, although in certain cases wildland fires can adversely affect both people and the environment. A wildland fire can interact with the surrounding topography, vegetation and weather in a complex manner, which makes microscale prediction of wildland fire behaviour difficult in many situations. This thesis focused on the application of the Weather Research and Forecast (WRF) numerical weather prediction (NWP) and WRF-Fire coupled atmosphere-fire models to investigating aspects of atmospheric interactions with wildland fire. The research covered a wide range of atmospheric scales, from a seasonal mesoscale analysis of fire weather conditions across New Zealand to a microscale analysis of complex atmosphere-fire interactions over idealised terrain. The first study investigated the suitability of WRF modelling of fire weather conditions for the 2009/10 wildland fire season in New Zealand. The WRF model horizontal grid spacing was 8 km and the model output was directly compared with near-surface fire weather conditions meaured and derived at 23 weather stations located throughout New Zealand. The analysis considered the air temperature, relative humidity, wind conditions, rainfall and the New Zealand Fire Weather Index (FWI) and Continuous Haines Index (CHI) on observed high-end fire weather days. WRF typically underpredicted the air temperatures and relative humidities, whereas it typically overpredicted the wind speeds, CHI and the number of high-end fire weather days. WRF was assessed to be unsuitable for accurately modelling particular aspects of fire weather, such as the wind speed and direction, in mountainous terrain and near complex coastlines. Further research is needed to investigate how varying the horizontal resolution in WRF affects the assessed accuracy of modelled fire weather conditions. The second study investigated the behaviour of the Haines Index (HI), CHI and FWI, and their associated atmospheric properties for the 2009/10 wildland fire season in New Zealand. The analysis demonstrated that there was a large degree of spatial variability in fire weather conditions throughout New Zealand, particularly in or near mountainous terrain. The fire weather severity was highest in the eastern South Island and appeared to be closely associated with mesoscale atmospheric processes over mountainous terrain, although the relationship between these atmospheric processes and fire weather condi- tions requires further investigation. The HI and CHI were both limited in their utility at measuring aloft fire weather conditions in high altitude regions. Finally, the fire weather conditions associated with the 36 largest wildland fires of the fire season were evaluated, although no statistical relationships were found between the wildland fire size and either the CHI or FWI. The third study investigated the fire weather conditions across the South Island associated with an extreme foehn event on 6 February 2011. Mountain waves developed in the northwesterly synoptic flow over the Southern Alps and were found to directly influence the fire weather conditions near the surface and aloft in the lee of the mountains. A hydraulic jump along the foothills of the Canterbury Plains resulted in a downslope windstorm with wind speeds exceeding 80 km/h. Further south, large amplitude mountain lee waves directly influenced the near-surface wind speeds and atmospheric stability aloft. The foehn winds were associated with peak air temperatures over 35˚C in the eastern South Island, which are significantly higher than the climatological average. The FWI indicated widespread extreme near-surface fire weather conditions in the lee of the mountains. The subsequent passge of a cold front on 7 February brought a marked reduction in fire weather severity across the South Island. The fourth study investigated atypical wildland fire behaviour on steep leeward slopes through a series of idealised WRF-Fire simulations. The analysis considered both the leeward flow characteristics over a triangular ridge line and the fire spread from an ignition point at the base of the leeward slope. The fire spread was modelled for two different fuel types and with two-way atmosphere-fire coupling both enabled and disabled. The modelled fire spread in the heavy fuel type with coupling enabled closely resembled the fire channelling wildland fire behaviour phenomenon. The initial fire spread was initially dominated by upslope fire spread to the mountain ridge line at an average rate of around 2.0 km/h. This was followed by a phase of intermittent rapid lateral fire spread close to the ridge line at a maximum rate of around 3.6 km/h. The intermittent rapid lateral fire spread was driven by strongly circulating horizontal near-surface winds that were associated with updraft-downdraft interfaces. These updraft-downdraft interfaces formed due to an interaction between the strong pyro-convection and terrain-modified winds. The presented research collectively demonstrated the versatility and effectiveness of NWP and coupled atmosphere-fire modelling for studying various aspects of atmospheric interactions with wildland fire. The research further highlighted the effects of atmospheric processes over complex terrain on fire weather conditions and wildland fire behaviour. Although three of the studies in the thesis had a regional focus on New Zealand, the research outcomes should benefit end users in fire management worldwide.

With over 10,000 acres burned in wildland fires in 2014 in Mississippi, accurate fire hazard prediction is of great importance. Soil moisture, fuel moisture, and fire hazard are inextricably linked. Remote estimation of soil moisture in the Southeastern United States for fire hazard modeling is hampered by the use of models engineered for other physiographic regions and the prevalence of deep, fast-draining sands underneath heavy vegetation. United States Geologic Service hydrographs were investigated and compared to nearby soil moisture and precipitation readings in an attempt to identify the links between stream gauge readings and watershed soil moisture. Stream gauge peaks corresponded within a three day window of soil moisture peaks 73.3% of the time, with 43.8% of peaks occurring simultaneously, thus verifying the indicative nature of local hydrographs. With further study, this easily accessed proxy variable could enhance currently used soil moisture models and drought indices.

Current field models for wildfire prediction are mostly based on dry or low-moisture fuel combustion research. To better study live fuel combustion behavior and develop the current semi-empirical bush combustion model, a laminar flow flat-flame burner was used to provide a convection heating source to ignite individual live fuel samples. In this research project, four Utah species were studied: Gambel oak (Quercus gambelii), canyon maple (Acer grandidentatum), big sagebrush (Artemisia tridentata) and Utah juniper (Juniperus osteosperma). Leaf geometrical parameters and time-dependent combustion behavior were recorded. Qualitative results included various combustion phenomena like bursting, brand formation and bending. Quantitative results included determination of best correlations for (a) leaf geometrical properties (individual leaf dry mass (mdry), thickness (Δx), leaf width (W) and leaf length (L)) and (b) combustion characteristics (e.g., time to ignition (tig), time of flame duration (tfd), time to maximum flame height (tfh), time to burnout (tbrn), and maximum flame height (hf,max)). A semi-empirical bush model was expanded to describe the combustion behavior of the three Utah species (Gambel oak, canyon maple and Utah juniper). Leaf placement and bush structure were determined from the statistical model. A new flame area simulation was explored in the semi-empirical bush model in order to improve the bush burning predictions.

Historical land use and changes in climate have altered fire behavior and severity in fire-prone ecosystems of western North America. A variety of fuels treatments are used to abate fire hazard, restore ecosystem processes, and increase forest resilience. Mechanical fuels treatments are increasingly used to alter forest structure and fuel continuity due to impediments to the use of prescribed fire. An increasingly common fuels treatment is mechanical mastication. Mastication does not remove fuels, but instead rearranges live and dead vertical woody fuels into a compacted layer on the forest floor. While mastication reduces potential fire intensity, these compacted fuels are flammable and capable of causing tree mortality and other negative ecological consequences when they burn in prescribed fires or wildfires. A current knowledge gap is quantitative information about the rate at which masticated fuels decompose and the rate at which vegetation reestablishes within sites previously masticated. Using 25 sites across northern California and southern Oregon, this thesis examines how masticated fuels change over time. Results from this study demonstrate that the majority of mass lost from masticated fuel beds occurred in the 1 and 10-hour woody fuel classes. Because surface fire behavior is driven by these fine fuels, these findings are valuable to the planning and retreatment of masticated fuels treatments and the corresponding fire suppression efforts in masticated sites. In combination with masticated wood surface fuels, shrubs and small trees play an important role in fire behavior, acting as ladder fuels that exacerbate surface fire behavior and threaten to ignite residual trees. A lack of understanding of how woody vegetation recovers following masticated fuel treatments gives rise to questions and challenges regarding treatment longevity. In this study, species with the ability to resprout tended to recover more quickly than obligate seeding species. Residual conifer saplings or trees that establish in masticated fuelbeds also recovered rapidly, reducing the efficacy of fuels treatments. Future implementation of masticated fuels treatments should consider both woody fuel decomposition and the corresponding recovery of shrubs and small trees to maximize treatment longevity. / Master of Science

Any rere any milions d'hectàrees són destruïdes pels incendis forestals, no només a Europa sinó arreu del món, tan sols cal recordar els dramàtics episodis viscuts a Califòrnia i Austràlia recentment. A banda de l'evident impacte mediambiental que això provoca -emissió de gasos d'efecte hivernacle, pèrdua de biodiversitat, acceleració de l'erosió del sòl, etc.- els incendis són també un problema social de primer ordre, que posa en perill a les persones i els seus béns. Davant d'aquesta situació, en les darreres dècades s'ha impulsat fortament la recerca en l'àmbit dels incendis forestals. Tanmateix, l'estudi dels incendis forestals és certament complex per les condicions i l'entorn on aquests es desenvolupen, a banda també del gran nombre de fenòmens -físics, químics i socials- que interaccionen al llarg de diferents escales espacials i temporals, per a donar lloc a l'inici i propagació del foc. És per això que bona part de la recerca sobre el comportament dels incendis forestals ha tingut lloc bàsicament al laboratori, tot i que qüestions com ara com traslladar aquests resultats experimentals als incendis reals, o bé fins a quin punt aquest tipus d'experimentació és útil o què és el que realment es pot extrapolar i què no, no han tingut encara cap resposta clara.L'objectiu d'aquesta tesi ha estat doncs el de contribuir a l'estudi del canvi d'escala en l'experimentació en incendis forestals pel què fa al comportament del foc, mitjançant les tècniques de l'anàlisi dimensional i de semblança. En primer lloc s'ha realitzat una extensa revisió bibliogràfica centrada bàsicament en aquells treballs que havien aplicat d'alguna manera o altra l'anàlisi dimensional i de semblança a l'estudi dels incendis i en particular dels incendis forestals. S'ha vist que no es possible realitzar un escalatge complet d'aquest fenomen i que el més utilitzat ha estat l'escalatge de Froude. A més s'ha detectat que mai abans s'ha aplicat aquest tipus d'anàlisi als models que s'utilitzen normalment avui dia en l'experimentació de laboratori. A continuació s'ha fet doncs una anàlisi exhaustiva de totes les variables que determinen el comportament d'un incendi forestal en els diferents escenaris experimentals (de laboratori i de camp). A partir d'aquestes variables s'ha realitzat una anàlisi dimensional per a estudiar la propagació d'un front de flames -tan bàsic com en condicions de vent i pendent- així com una anàlisi de semblança que ha permès obtenir les lleis d'escala per a les diferents variables que caracteritzen la propagació d'un incendi forestal. S'ha dissenyat i executat un programa experimental al laboratori amb l'objectiu de validar si es complien les lleis d'escala trobades i de determinar-ne el rang de validesa i les possibles causes en cas que no es complissin.Els resultats obtinguts han mostrat que per a fronts de flama bàsics propagant-se sense vent ni pendent, totes les variables analitzades segueixen les lleis d'escala derivades de l'estudi teòric, en el rang de longituds de front de flama abraçat que va dels 25 cm als 3 m. Nogensmenys cal remarcar que paràmetres com la humitat i el tipus de combustible o les característiques de la instal·lació experimental utilitzada poden alterar enormement els resultats si no es controlen adequadament. En el cas dels fronts de flama propagant pendent amunt, els resultats han mostrat que les lleis d'escala de la geometria de flama es compleixen per a tot el rang de pendents estudiat que va de 0 fins a 30°, mentre que en el cas de la llei d'escala de la velocitat de propagació deixa de complir-se per a pendents de 30°. Finalment, en el cas dels fronts de flama propagant en condicions de vent, els resultats han mostrat que per a velocitats del vent superiors a aproximadament 2,5 m/s les lleis d'escala tant de la velocitat de propagació com de la geometria de flama deixen de complir-se.Al final d'aquest treball s'apunten les causes que poden conduir a l'incompliment de les lleis d'escala així com als factors que poden restar validesa als experiments efectuats a escala de laboratori, quan es vol extrapolar els resultats a escales més grans o fins i tot a incendis reals. / Year after year millions of hectares are destroyed by wildland fires, not only in Europe but all over the world; just remember the dramatic episodes recently occurred in California or Australia. Besides the evident environmental impact caused by these fires -emission of greenhouse gases, biodiversity loss, soil erosion, etc- wildland fires represent also a social problem of primary order that threatens human life and their assets.Because of this situation, during the last decades research on wildland fires has been greatly boosted. Nevertheless, the study of forest fires is really complex due to the conditions and the environment in which they develop and to the number of phenomena -physical, chemical and social- that interact all along the different spatial and temporal scales that give rise to the start and development of a fire. That is partly the reason because the study of wildland fire behaviour has mainly been developed in laboratories, but questions like how these experimental results can be translated to real fires?, or is really this kind of experimentation useful?, or what can be extrapolated? These questions have not yet received a clear answer.The goal of this work was to improve the knowledge on the effect of changing the scale in the experimental study of forest fire behaviour, by means of dimensional and similarity analysis. First an extended bibliographic review has been done, centred on those works that had applied in one or another way the dimensional and similarity analysis to the study of fires and more specifically to forest fires. It was observed that it is not possible to undergo a complete scaling of a forest fire and that the most used partial scaling technique was the Froude scaling. Moreover it was detected that this kind of analysis was never before applied to the laboratory models used currently to obtain experimental data on wildland fires. Thus, an exhaustive analysis of all the variables affecting forest fire behaviour has been carried out for the diverse experimental scenario (in the lab and field). From these variables, a complete dimensional analysis has been developed in order to study the spread of a flames front -both in basic conditions and with slop or wind- and a subsequent similarity analysis has provided the scaling laws governing all the variables under study. A complete experimental program has been designed and developed in the laboratory with the aim of validating the scaling laws previously found and to establish the possible causes of any failure of the laws. The results obtained show that in the case of a basic flame front, spreading under no wind and no slope conditions, all the variables analysed followed the scaling laws obtained during the theoretical study for flames front lengths ranging from 25 cm to 3 m. For the tests under slop conditions, the results indicate that the scaling laws corresponding to the flame geometry are verified for all the slopes tested which range from 0 to 30°, while in the case of the rate of spread scaling law is no longer verified for the 30° slope. Finally, in the case of flame fronts spreading under wind conditions, the results show that for wind speed values greater than 2,5 m/s neither of the scaling laws corresponding to the flame geometry and the rate of spread, are verified. It has also been observed that parameters such as moisture content, the type of fuel or the specific design of the experimental device used can have a big influence on the results obtained if they are not adequately controlled.At the end of this work, the main causes leading to the failure of the scaling laws are pointed out together with the factors that can make the laboratory experiments less reliable when trying to extrapolate the results to larger scales or even to real fires.

After decades of suppression, fire is returning to forests of western United States. Understanding responses of wildlife species to fire is essential to native species conservation because contemporary fires may not have the same effects on forest structure and landscape patterns as historical fires. I used radio-telemetry to investigate effects of fire severity and heterogeneity on habitat selection of Mexican fox squirrels, Sciurus nayaritensis chiricahuae. Vegetation within home ranges was characterized by more open understory and larger trees than random locations. Squirrels used areas burned at low severity more than unburned areas and those burned at higher severities. Squirrels used areas of moderate burn heterogeneity more than areas of low or high heterogeneity. Return of low-severity fire can help restore habitat for Mexican fox squirrels and other native species in forests with a historical regime of low-severity fire and contribute to understanding of the role of fire in forest ecosystems.

The North American Monsoon System (NAMS) is a dominant factor in climate in the southwestern United States and northwestern Mexico. Despite the influence of the NAMS and the intense research efforts it receives, its predictability, its variability, and the details of its influence on the environment are not well understood. This dissertation is comprised of three papers, which collectively address these three aspects of this complex climate phenomenon through an examination of various data and analyses at multiple spatial and temporal scales, while focusing on impacts in southern Arizona. In the first paper, a modified definition of the NAMS is established to delineate dates for monsoon onset, bursts, breaks, and retreat. The results are applied to an atmospheric compositing study in the second paper and to an applied study of monsoon-wildland fire relationships in the third paper. In the second paper, geopotential height patterns that affect moisture advection are identified. Onset, retreat, and break timing and duration are impacted by shifts in the latitude of the mid-level anticyclone and by lower-level gradients and contour orientation. Analyses in the third paper reveal the some of the complex effects of monsoon onset, variations in break timing and duration, and monsoon retreat on fire occurrence. This research contributes to the current knowledge of the NAMS in general and to the specific regional impacts of the monsoon. The results can (1) improve meteorological forecasts through the recognition of synoptic and sub-synoptic patterns related to the NAMS and (2) help fire managers by expanding the current understanding of the regional controls of wildland fire.