The wildland–urban interface dynamics in the southeastern U.S. from 1990 to 2000

Resolving environmental impacts caused by the wildland–urban interface (WUI) expansion such as wildlife habitat fragmentation, or increased fire risk entails an accurate delineating of WUI boundary and its dynamics prediction. This study identified WUIs throughout the 11 states of southeastern U.S. in 1990 and 2000 and observed their change during this period utilizing census surveyed housing density and remotely sensed land-cover data. In 1990 and 2000, states of North Carolina and Virginia had the highest, while the state of Arkansas had the lowest proportion of WUI coverage. From 1990 to 2000, states of South Carolina, Florida and Mississippi have seen a radical WUI expansion, while North Carolina has experienced no noticeable WUI transformation. Total WUI area increased from 241,983 km² in 1990 to 285,415 km² in 2000. Wildland–urban interface patch number decreased from 1362 to 1282 and mean WUI patch size enlarged from 178 km² to 233 km². Total WUI area in each single year and new added WUI from 1990 to 2000 have high sensitivity to threshold adjustment of low housing density, vegetation density, while subtle sensitivity to threshold modification of high housing density. Vegetation density is a more significant factor than housing density in determining WUI coverage in both 1990 and 2000 and WUI dynamics from 1990 to 2000 in each state. Urban aggregation index is a significant factor related with WUI coverage in each state as well.     

Modeling wildfire potential in residential parcels: A case study of the north-central Colorado Front Range

This study evaluated if present-day wildfire potential (i.e. potential fireline intensity and percentage crown fire) differs for residential parcels developed at different time periods in the north–central Colorado Front Range. To answer this question, a model of wildfire potential was built based on 2001 fuels and vegetation and compared the output to actual fire severity of the 2002 Hayman and 2004 Picnic Rock fires (measured by satellite imagery). Except for low-load fuel types such as grass, the modeled wildfire potential corresponded well to observed fire severity. Wildfire potential was then evaluated within 7 classes: developed (1880–1944, 1945–1959, 1960–1974, 1975–1989, 1990–2005) and undeveloped (either zoned or not zoned for development). The results suggest that there is one class characterized by relatively low wildfire potential (developed 1880–1944) and three classes characterized by relatively high wildfire potential (developed 1960–1974 and the two undeveloped parcel classes). These results hold both for 99th percentile (extreme) and 50th percentile (average) fuel conditions. The results suggest that under current zoning regulations, future structures are likely to be built on parcels that, on average, have somewhat higher potential fireline intensity and higher percentage of crown fire compared to currently developed parcels. However, the location of future development may be influenced by forest changes, such as the visual degradation and perceived fire hazard of trees killed by the continuing mountain pine beetle outbreak. Overall, this study introduces an improved method for quantifying wildfire potential in the rapidly developing wildland–urban interface that could be applied to other areas.     

Development of rapidly deployable instrumentation packages for data acquisition in wildland–urban interface (WUI) fires

In an effort to quantify structure ignition mechanisms during wildland–urban interface (WUI) fires, rapidly deployable instrumentation packages were developed. For a structure under a WUI fire attack, the packages are designed to: (1) provide temporally resolved images of structure ignition mechanisms and (2) provide quantitative data on total heat flux, wind speed, wind direction, ambient temperature, and relative humidity near a structure. The unique design of the packages allowed for wireless transmission of all data signals collected to a hardened location. Prior to attempting to use these instrumentation packages in real WUI fires, a proof-of-concept test was conducted under a prescribed fire. In these tests, a shed was used as a surrogate for a typical structure that would be found in the WUI. The proof-of-concept test was successful and has demonstrated that relatively inexpensive instrumentation can be used to image structure ignition in the path of an approaching crown fire and that directional flame thermometers (DFT) were acceptable instrumentation to measure total heat flux in place of cumbersome water cooled total heat flux gages.     

Wildland fire spot ignition by sparks and firebrands

Wildland and Wildland Urban Interface (WUI) fires are an important problem in many areas of the world and may have major consequences in terms of safety, air quality, and damage to buildings, infrastructure, and the ecosystem. It is expected that with climate changes the wildland fire and WUI fire problem will only intensify. The spot fire ignition of a wildland fire by hot (solid, molten or burning) metal fragments/sparks and firebrands (flaming or glowing embers) is an important fire ignition pathway by which wildfires, WUI fires, and fires in industrial settings are started and may propagate. There are numerous cases reported of wildfires started by hot metal particles from clashing power-lines, or generated by machines, grinding and welding. Once the wildfire or structural fire has been ignited and grows, it can spread rapidly through ember spotting, where pieces of burning material (e.g. branches, bark, building materials, etc.) are lofted by the plume of the fire and then transported forward by the wind landing where they can start spot fires downwind. The spot fire problem can be separated in several individual processes: the generation of the particles (metal or firebrand) and their thermochemical state; their flight by plume lofting and wind drag and the particle thermo-chemical change during the flight; the onset of ignition (smoldering or flaming) of the fuel after the particle lands on the fuel; and finally, the sustained ignition and burning of the combustible material. Here an attempt has been made to summarize the state of the art of the wildfire spotting problem by describing the distinct individual processes involved in the problem and by discussing their know-how status. Emphasis is given to those areas that the author is more familiar with, due to his work on the subject. By characterizing these distinct individual processes, it is possible to attain the required information to develop predictive, physics-base wildfire spotting models. Such spotting models, together with topographical maps and wind models, could be added to existing flame spread models to improve the predictive capabilities of landscape-scale wildland fire spread models. These enhanced wildland fire spread models would provide land managers and government agencies with better tools to prescribe preventive measures and fuels treatments before a fire, and allocate suppression resources and issue evacuation orders during a fire.     

Review of Pathways for Building Fire Spread in the Wildland Urban Interface Part I: Exposure Conditions

While the wildland–urban interface (WUI) is not a new concept, fires in WUI communities have rapidly expanded in frequency and severity over the past few decades. The number of structures lost per year has increased significantly, due in part to increased development in rural areas, fuel management policies, and climate change, all of which are projected to increase in the future. This two-part review presents an overview of research on the pathways for fire spread in the WUI. Recent involvement of the fire science community in WUI fire research has led to some great advances in knowledge; however, much work is left to be done. While the general pathways for fire spread in the WUI (radiative, flame, and ember exposure) are known, the exposure conditions generated by surrounding wildland fuels, nearby structures or other system-wide factors, and the subsequent response of WUI structures and communities are not well known or well understood. This first part of the review covers the current state of the WUI and existing knowledge on exposure conditions. Recommendations for future research and development are also presented for each part of the review.     

Farmers,fires, and forests: a green alternative to shifting cultivation for conservation of the Maya forest?

When fires blazed through Mexico's forests in 1998, the country experienced a new sense of urgency in its attempts to combat ecosystem degradation and loss of biodiversity. Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT, the federal environmental protection agency) identified the use of fire in agriculture as a major contributor to the conflagration. Traditional “slash-and-burn” systems are still widely practiced in the southeast of Mexico, and finding a substitute for burning, especially in and near protected areas, became imperative (SEMARNAT, 2001). Experience from different parts of Central America indicated that green manure/cover crop systems (g/cc) could increase soil fertility, reduce erosion, control weeds and raise the yield of maize; the hope was that this system could replace slash-and-burn practices with their attendant risk of forest fires. We present the case study of a project introducing a green cover crop to traditional, resource-poor, maize farmers in one community of the Yucatan peninsula and preliminary results from a similar project in the Calakmul Biosphere Reserve, discussing the data in the light of the on-going debates concerning both fire policy and soil erosion. We conclude that, in spite of demonstrating some advantages, adoption in the peninsula has been hindered by environmental, economic and socio-cultural factors. Mexican efforts to eliminate fire from the forests must also be assessed with reference to the scientific literature by fire experts and historical ecologists, indicating that prohibition of small fires may actually decrease total biodiversity, while increasing the probabilities of catastrophic forest fires.     

Mercury distribution in two Sierran forest and one desert sagebrush steppe ecosystems and the effects of fire

Mercury (Hg) concentration, reservoir mass, and Hg reservoir size were determined for vegetation components, litter, and mineral soil for two Sierran forest sites and one desert sagebrush steppe site. Mercury was found to be held primarily in the mineral soil (maximum depth of 60 to 100 cm), which contained more than 90% of the total ecosystem reservoir. However, Hg in foliage, bark, and litter plays a more dominant role in Hg cycling than the mineral soil. Mercury partitioning into ecosystem components at the Sierran forest sites was similar to that observed for other US forest sites. Vegetation and litter Hg reservoirs were significantly smaller in the sagebrush steppe system because of lower biomass. Data collected from these ecosystems after wildfire and prescribed burns showed a significant decrease in the Hg pool from certain reservoirs. No loss from mineral soil was observed for the study areas but data from fire severity points suggested that Hg in the upper few millimeters of surface soil may be volatilized due to exposure to elevated temperatures. Comparison of data from burned and unburned plots suggested that the only significant source of atmospheric Hg from the prescribed burn was combustion of litter. Differences in unburned versus burned Hg reservoirs at the forest wildfire site demonstrated that drastic reduction in the litter and above ground live biomass Hg reservoirs after burning had occurred. Sagebrush and litter were absent in the burned plots after a wildfire suggesting that both reservoirs were released during the fire. Mercury emissions due to fire from the forest prescribed burn, forest wildfire, and sagebrush steppe wildfire sites were roughly estimated at 2.0 to 5.1, 2.2 to 4.9, and 0.36+/-0.13 g ha(-1), respectively, with litter and vegetation being the most important sources.     

Protecting Lives and Property in the Wildland–Urban Interface: Communities in Montana and Southern California Adopt Australian Paradigm

Threats to people and property in the wildland–urban interface have taken on global proportions. It is becoming increasingly rare to have a wildland fire incident that does not involve people and their homes. In addition to Australia and North America, people have died in interface fires in Europe, Africa, and Asia, including 212 people who died in the devastating forest fires in northeastern China in May 1987. The prevailing interface model is one that attempts to evacuate people away from fire areas to get them out of harm’s way. This traditional approach in the U.S. has been preferred by law enforcement agencies and fire services. The problem with this model is that evacuation warnings are often late to non-existent, leading to the deaths of interface residents entrapped by fires on highways as they try to escape. For example, 16 people suffered lethal burns when the 2003 Cedar and Paradise Fires in California overran them as they were trying to evacuate. Two communities in the United States have adopted variations of the Australian model of Prepare, Go Early, or Stay and Defend (P/GE/SD). Officials in the Painted Rocks Fire District, Montana, and Rancho Santa Fe, California, were interviewed to determine how the Australian model was being implemented. Two of the authors have firsthand experience with these two case examples. P/GE/SD has been tested successfully at both locations. The Australian model, however, is under review following the Black Saturday fires of February 2009 in Victoria, Australia. The objective of this paper is to present specific ideas that can be used to reform and improve fire policy, planning, and performance in the Wildland–Urban Interface in the United States.     

超长海底隧道无竖井排烟及补风量优化研究

摘 要：超长海底隧道结构特殊,排烟补风成为制约超长海底隧道发展的关键因素。依托烟大海底隧道提出超长海底隧道无竖井排烟系统,并设计新型的海中无竖井排烟补风方案——采用离心式空气压缩机将火灾烟气高速加压后排到海水中,并通过压缩空气进行额外补风。采用FDS对不同排烟量和补风量下56组工况进行模拟,通过分析烟气层厚度、排烟效率和能见度,寻找最优的排烟补风方案。结果表明：排烟量在140~180,190~210 m3/s,补风量分别占排烟量的50%、70%时,系统排烟效果最优;其中,排烟量180 m3/s,补风量50%和排烟量200 m3/s,补风量70%情况下的排烟效果最优,且后者优于前者。实际工程应用中,可以考虑设计排烟量为200 m3/s,补风量为140 m3/s。     

A Case Study of a Community Affected by the Witch and Guejito Wildland Fires

Wildland-urban interface (WUI) fires occur when fire spreads through both wildland and community (structures and vegetation) fuels. These fires are capable of causing significant destruction to both the built and the natural environments. When these fires occur under extreme fire danger conditions (e.g., high winds, low humidity) and in areas of significant population (e.g., San Diego, California) firefighters, and other emergency responders, are significantly challenged by the combination of firefighting and aiding the public. This paper presents the results of an in-depth case study of a community of 274 residences which was subjected to two wildland fires (within 2.5 h of each other) during the October 2007 firestorm in southern California. A significant amount of effort was spent obtaining information from residents and emergency responders to determine the fire spread timeline, structure ignition mechanisms, and defensive actions. Of the 274 residences, 245 were within the fire perimeter, 74 were destroyed, and 16 were damaged. When the first fire front arrived, the rate of structure ignitions peaked at 21 per hour. Direct and indirect ember, or firebrand, attack was responsible for the ignition of 2/3 of the destroyed homes. Defensive actions were taken on one of every three homes. Of the 16 damaged homes, 15 were successfully defended. Further study of this community is ongoing to investigate what currently recommended pre-fire hazard reduction actions could be, and were, implemented and their effectiveness at reducing the likelihood of structure ignition.     

The effect of a wildfire on stream water quality and catchment water yield in a tropical savanna excluded from fire for 10 years (Kakadu National Park, North Australia)

The wet/dry tropics of the Australian savannas are particularly prone to fire due to the highly seasonal rainfall and accumulation of grassy fuels. The effect of an early dry season wildfire (May, 1998) on the water quality of a seasonally flowing stream (December-June) was examined for a lowland savanna forest in Kakadu National Park (northern Australia) which had remained unburnt for 10 years. The water quality variables assessed were: total and volatile suspended sediment, phosphorus, nitrogen, iron and manganese. Compared to three years of pre-fire water quality data and 5 years of stream flow data, there was no detectable impact of the wildfire on the volume of stream flow, mean concentrations and the total mass transported by the stream for each water quality variable, except possibly nitrogen. The limited effect on water quality is attributed primarily to the timing of the wildfire and the low intensity relative to fires later in the dry season (September). The retention of canopy cover and the accumulation of leaf litter following the wildfire, and the catchment's gently undulating terrain all contributed to the negligible impact on water quality. Early dry season fires appear to be a viable management option for reducing accumulated fuel loads and hence reducing the risk of destructive wildfires later in the dry season.     

The trouble with fire intensity

The author discusses the inadequacies and limitations of the term “fire intensity” as it is used to describe the severity of forest fires and suggests that the term “fire front power” is more appropriate. General Physical Scientist, Southeastern Forest Experiment Station, USDA, Forest Service, Macon, Georgia.     

森林灭火安全防范与紧急避险探讨

森林火灾受地形、植被、气象等因素影响,火势瞬息万变,险情难以预料。扑救森林火灾,极易发生人员伤亡。结合森林消防队伍长期灭火实战,探索性地研究了安全灭火的行动原则和火场需要严密防范的危险地形、危险植被类型、危险时段及特殊林火行为,并针对火场突发险情,提出了常用的紧急避险方法。     

山火引发输电线路跳闸事故的统计与分析

通过对部分引发输电线路跳闸的火灾事故进行统计以及对典型火烧迹地的跳闸事故进行考察,分析山火发生的次数、跳闸率、地理位置、过火区域地形地貌等,探讨引发线路跳闸的潜在山火类型、形成过程、影响因素和特性参数以及跳闸输电线路的放电特性参数。结果表明:易引发跳闸的山火类型依次为中高速中高强度的地表火、树冠火、冲冠火和地表火转化的树冠火;火灾基本为上山火,易形成高火焰、高热量、高温度、高浓度(烟尘粒子和带电质点)的易导致线路跳闸的环境条件;发生跳闸时输电线路主要放电部位为子导线,放电方式依次为对树、相间和对地;在中高强度火灾条件下放电距离突破了输电线路正常运行所需安全间隙,产生流注而发生跳闸。     

Predicted effects of residential development on a northern Idaho landscape under alternative growth management and land protection policies

Land use change driven by exurban development can lead to dramatic alterations in the structure and function of landscapes. Residential development outside of urban and suburban zones can disrupt agricultural and forest management operations and ecosystem processes, increase community wildfire hazard, deplete groundwater resources, and lead to social conflict. We assessed two policy tools, urban growth boundaries and agricultural use zoning, for their potential to help manage growth and sustain the rural landscape. Using a survey-based model, we simulated the effects of the two policy tools on land use change and compared the results with predictions of land use change for two rural counties (4794 km²) in northern Idaho developed in a previous project. We measured the effects of predicted exurban development using four measures: number of housing units predicted on productive agricultural lands, number of housing units predicted on a groundwater resource area, changes to a wildfire hazard index for residential structures, and the social acceptability of residential development patterns given current development preferences. The two policy tools impose in substantially different landscape-level residential development patterns when compared to the baseline change prediction and each other. Each tool resulted in a variety of tradeoffs between negative and positive effects among our measures of impact. Our findings demonstrate the importance of using multiple indicators to evaluate growth management and land protection policy tools for making land use planning decisions.     

Climate change and forest fires

This paper addresses the impacts of climate change on forest fires and describes how this, in turn, will impact on the forests of the United States. In addition to reviewing existing studies on climate change and forest fires we have used two transient general circulation models (GCMs), namely the Hadley Centre and the Canadian GCMs, to estimate fire season severity in the middle of the next century. Ratios of 2 x CO2 seasonal severity rating (SSR) over present day SSR were calculated for the means and maximums for North America. The results suggest that the SSR will increase by 10-50% over most of North America; although, there are regions of little change or where the SSR may decrease by the middle of the next century. Increased SSRs should translate into increased forest fire activity. Thus, forest fires could be viewed as an agent of change for US forests as the fire regime will respond rapidly to climate warming. This change in the fire regime has the potential to overshadow the direct effects of climate change on species distribution and migration.     

The Propensity of Wooden Crevices to Smoldering Ignition by Firebrands

Fire Technology - Fires occurring at the wildland-urban interface (WUI) have rapidly increased in frequency and severity over the past few decades. As a result of these extreme fires, multiple...     

广西地区山火引起高压线路跳闸环境特征研究

针对2006-2010 年广西电网超高压输电公司统计的线路遭遇山火状况,研究山火引起线路跳闸的环境特征,包括地形因素、可燃物状况以及山火行为特征,提出应对的控制和防治措施。并以广西地区为研究对象,获取研究区内气象站地面气象资料月值数据,包括平均气温、降水量、最小相对湿度以及1999-2004 年的森林火灾数据,分析气候因素对山火发生的影响。结果表明：广西森林火灾主要发生在冬季和春季,分别占总次数的37.4%和37.0%,夏季很少发生火灾;冬季发生火灾的过火面积所占比例最高,占46.8%,其次为春季,占33.7%;其中,百色市、柳州市、梧州市发生火灾较多,山火造成线路跳闸率分别为9.2%、125.0%、4.7%。山火引发跳闸地点可燃物类型主要为杂树、杂草、松树和杉树,树木树龄多为3-21 年（3 年以上居多）,胸径2～45 cm（10 cm 以上居多）,树高2.0～23.0 m（5.0～10.0 m 居多）,跳闸地点均出现在阳坡,坡度为16°～80°,其中<30°的缓坡和30°～60°的斜坡出现次数最多,分别占56%和36%;引起高压线路跳闸最主要的火灾类型是快速、中度地表火以及稳进树冠火,蔓延速度在2.1 m/min 以上,火焰高度在1.5 m 以上,火强度在750 W/m2 以上,建议根据山火发生的特殊性,加强山火高发地区的早期预警、火灾监测和可燃物管理等防控措施,减少山火引起输电线路跳闸,保障居民正常生活和社会稳定。