【作者】 王秋华；

【导师】 舒立福；

【作者基本信息】 中国林业科学研究院 ， 森林保护学， 2010， 博士

【摘要】 森林火灾具有突发性、随机性和任意性,有一个逐步形成、发生、发展的过程。当一般森林火灾受到特殊火场环境的综合作用时,会有很大的随机性和不可抗拒性。森林火灾又是世界上救助较为困难的自然灾害之一,扑救森林火灾具有极高的危险性。森林火灾变化无常,几乎没有两次相同的火灾。火灾发生后,预测、预报林火蔓延速度、能量释放、火强度以及扑火难易程度对森林火灾的扑救,配备人力和物力等具有很重要的意义。研究林火行为有助于及时掌握林火的发生发展,准确的掌握在何时何地在何种条件下会发生林火,有助于事先做好充分准备,有助于做出正确的决策,有助于更加有效、安全地进行扑火,避免事故的发生。但火行为的研究与发展比较缓慢,因为林火的复杂性和林火的试验比较难进行。国外的研究人员仍在改进现有的林火蔓延模型,并应用到火险等级预报、林火发生预报系统中。冰雪灾害后,在实地调查了湖南省受冰雪灾害影响的林分及新发生的火烧迹地,设置了野外样地,采集了样品。测定、分析了含水率、可燃物载量等因子,计算了火蔓延速度等火行为参数。结果表明:冰雪灾害后森林中有效可燃物负荷量在短期内成倍地增长,可燃物厚度增加,连续性变强,含水率逐渐降低。在调查的样地中,最低载量为12.23t/hm2,最高达到了50.26t/hm2,有5个样地超过20t/hm2。火环境发生了改变,火行为变得非常复杂:林火蔓延速度增强,面积蔓延速度、周长蔓延速度分别为111.67～972.71 m2/min,427～790m/(24)h;火强度更高,为675～7 500 kW/m,平均超过3 500 kW/m,具备了大火的特征;火烧非常彻底,可燃物的消耗量超过85%;释放的能量大,对树木的损害也非常大,火烈度超过95%。收集气象等资料,实地调查大兴安岭地下火火烧迹地,设置野外样地,并采取对照地,各采集样品。测定地下可燃物的含水率、载量、热值、点着温度、灰分含量等因子,从火烧迹地形状、燃烧深度、地下火的分类角度来分析地下火的火行为。结果表明:大兴安岭地下火的燃烧与可燃物干燥程度以及气象条件密切相关,旱情越严重,地下火越多;在3～4月份,平均气温在O℃以下,即使土壤封冻,也可能发生地下火;小叶樟草甸的生产力比较高,在腐烂、分解后不断地沉积,形成腐殖质或者泥炭,构成了地下可燃物。半分解物和腐殖质的点着温度比较高,分别为405℃,525℃,但即使达到这些点着温度,火焰也不是很明显,同时也很难得到具体的热值指数,原因都可能和灰分含量过高有关。受可燃物的厚度、坚实度及含水率的影响,地下火的火行为非常复杂,火强度只能采取燃烧深度近似计算,燃烧深度为15～30 cm;火烧迹地形状为鸡爪形插花状或不规则形插花状;以燃烧对象对地下火分类,可近似分为弱地下火和强地下火。根据野外调查结果,基于森林亚类型,从森林可燃物的角度,以主要伴生树种或下层植被为基础,根据云南主要针叶林分布区的自然条件与林分结构特点以及可燃物的各种特征对主要针叶林可燃物进行划分。依据云南主要针叶林的生态习性、可燃物的配置结构等,把可燃物类型简化为:灌木-云南松林,草类-云南松林;灌木-思茅松,草类-思茅松;灌木-华山松,草类-华山松等六个主要类型。测定云南主要针叶林云南松林、思茅松林和华山松林的可燃物特征参数,包括载量、表面积体积比、可燃物床厚度、死可燃物熄灭含水率、死可燃物热值和活可燃物的热值。建立6个可燃物模型,将其输入到BehavePlus模型,评估各可燃物类型潜在的火行为。结果表明,云南主要针叶林潜在的火行为十分剧烈,其中,灌木-思茅松林的火行为最强,火焰长度为2～16m、火线强度5 000～12 0000 kw/m、单位面积热量为20 000～27 000 kJ/m2、最大蔓延速率为10～270 m/min,而草类-华山松的火行为最弱,火焰长度为0.8～4.5m、火线强度为300～6 500kw/m、单位面积热量为12 000～18 000kJ/m2、最大蔓延速率为1～25m/min。这和可燃物的类型有关,也和所处的生境条件、立地有关。通过火烧迹地调查,可燃物的分析和飞火距离的模拟计算来研究云南松林的飞火,结果表明云南松的球果具有非常好的结构特征,在条件具备的时候,如气象条件,地形合适,很容易引起飞火。飞火移动的距离可用相关的公式来大概估算,估算的飞火距离在0.68km～1.87km,与2006年昆明安宁“3·29”大火产生的飞火距离大致相符合。更多还原

【Abstract】 Forest fires have their characteristics such as paroxysmal, stochastic and random, and they have steps from shaping, erupting, and extinguishing. At the same time, forest fire are one of the most difficult natural disasters, it is very dangerous to fight with. When facing special environment, the fires will be random and fastness. The same fires can’t exist in the world are due to uncertainty and different losses.During fire, it is necessary to forecast and predict spread rate, energy releasing, fire intensity and degree of difficulty to fight with, in order to match human resource and equipments. Fire behaviors’research is helpful to master forest fire dynamics, prepare for fire occurring, well decision-making and fight effectively and safely. But the processes of research on fire behaviors are slowly because of fire behaviors’complex and experiments’difficulty.After snow and ice disasters, stands of forest and new burned areas in Hunan province were surveyed by setting field plots. Moisture content and fuel load were measured by sampling in order to calculate fire behaviors such as rate of spread et al. The results shown fuel load increased instantly, fuel thickness enhanced, fuel continuity swelled and moisture content decreased due to shrubs and herbs died. Load of fuel variated from 12.23t/hm2 to 50.26t/hm2, five sites exceeded 20t/hm2. With fire environment changing sharply, fire behaviors become complex and bring on fire fighters’fatalness. Fire square and perimeter rates of spread are 111.67～972.71 m2/min and 427～790 m/(24)h respectively, while fire intensity is 675～7 500kw/m, the average exceed 3 500 kw/m, with characteristics of conflagration. These fires consumed over 85 percents fuel, and released huge energy. Fire severity index exceed 85%.Meteorological information were collected from local weather bureau, fire sites and comparing plots in Daxing’anling were surveyed by setting field samples. At he same time, samples in these plots were gathered. Moisture content, fuel load, heat capacity, ignition point and ash content were measured in laboratory. Fire behaviors were analyzed from fire site shapes, combustion depth and ground fire classification. The results showed correlation between combustibility with dryness of fuels and meteorological conditions. In northeastern China, between March and April, even ambient temperatures are below zero and soil freezing, ground fires will occur. The production of Deyeuxia angustifolia meadow is so high that after rotting, decomposing, and depositing, they can easily change into ground fuels. Because of high ash content, it is hard to measure the heat capacity, while ignition points can be obtained. Ignition point of semi-decomposed layer and humus are 405℃and 525℃respectively. Due to thickness, compactness and moisture content, ground fire behaviors are complicated.In view of ecological character, fuel framework, based on forest sub-type and forest fuel characters, by field surveying forest structures and natural conditions, main conifers of Yunnan province can be simplified into 6 types, including Pinus yunnanensis with shrub, Pinus yunnanensis with grasses, Pinus kesiya var. langbianensis with shrub, Pinus kesiya var. langbianensis with grasses, Pinus armandii with shrub and Pinus armandii with grasses.By field surveying and lab experiments, indexes of 6 types of fuel characters including fuel loading, surface area-to-volume ratio, fuel bed depth, dead fuel extinction moisture content, heat of combustion of dead fuel and live fuel can be input BehavePlus model. Using outputs of indexes such as flame length, fireline intensity, heat per unit area, and surface rate of spread (maximum), potential fire behaviors can be evaluated. The results shown that fire behaviors of conifers complex. Fire behaviors of Pinus kesiya var. langbianensis -with shrub are strongest, its flame length, fireline intensity, heat per unit area and surface rate of spread (maximum) is 2～16m, 5 000～12 0000 kw/m, 20 000～27 000 kJ/m2 and 10～270 m/min respectively, while Pinus armandii -with grasses’are least, its flame length, fireline intensity, heat per unit area and surface rate of spread (maximum) is 0.8～4.5 m, 300～6 500 kw/m, 12 000～18 000 kJ/m2 and 1～25 m/min, respectively. The differences are ascribed to natural conditions, ecological habit and fuel characters.By burned sites surveying, fuel experiments, and modify spotting distance, the results shown that cones of Pinus yunnanensis have well structures for spotting, if condition are appropriate, such as weather and topography, they can easily spread. The spotting distance can be estimated from formula. The spotting distance of Anning fire site is between 1.24 km and 3.34 km, inosculate to actual distance.更多还原