大兴安岭塔河地区雷击火发生驱动因子综合分析

森林火灾是一个全球性问题,对森林资源和温室气体排放有重要影响,并严重影响人们生命财产安全。林火主要分为人为火(人为活动引起)和雷击火(雷电引起)两大类。在我国北方针叶林带,雷击火主要集中在黑龙江大兴安岭和内蒙古呼伦贝尔盟地区。大兴安岭塔河地区位于我国北方针叶林带,是森林火灾的重灾区。其中雷击火所占比例大约1/3以上。目前针对当地雷击火与影响因子的研究主要集中于气象因子,非气象因子(森林可燃物和地形特征)的研究受数据条件和技术手段限制研究报道较少。研究数据包含三部分,林火数据,气象数据和地理植被数据。林火数据包含1974—2009年间林火发生经纬度坐标,时间和面积等。气象数据主要包括每日尺度的最低气温,最高气温,平均风速,平均相对湿度等因子。根据加拿大火险天气指标系统计算出了出了细小可燃物湿度码(FFMC),干燥可燃物湿度码(DMC)和干旱码(DC)也没用于本研究。此外,基于1∶10万塔河地区数字化林相图提取了海拔、坡度、坡向、森林类型、优势树种、龄级等因子用于决策因子分析。研究数据分析过程主要应用Arc GIS10.0中的空间分析工具和SPSS19.0的逻辑斯蒂回归模型完成。研究结果显示"日最低气温","最大风速"和"最小相对湿度"3个气象因子及火险天气指标系统(FWI)中细小可燃物湿度码(FFMC)干旱码(DC)与雷击火发生概率显著相关(P0.05),模型整体拟合水平R2(CoxSnell)=0.326。在非气象因子与雷击火发生的逻辑斯蒂模型检验中,"地被物盖度"和"龄级"均在P=0.05水平上与雷击火发生显著相关,其模型的整体拟合水平R2(CoxSnell)为0.15。研究结论表明在分析雷击火发生的决策因子时,应该综合考虑气象、可燃物和林分因素。

Climatic and non-climatic factors driving lightning-induced fire in Tahe, Daxing'an mountain

Forest fires are a global issue due to their significant degradation of forest reserves and greenhouse gas emissions, as well as loss of human lives and livelihoods. Forest fires are mostly caused by nature (lightning-induced fires) and human activities (anthropogenic fires). Lightning-induced fires in China mostly occur in boreal forest, namely the Daxing''an Mountains of Heilongjiang province and Hulunbeier of Inner Mongolia. Lightning accounts for nearly a third of all forest fires in the Tahe area of the Daxingán Mountains. Most previous studies on lightning-induced fires have focused primarily on climatic factors, and studies of non-climatic factors such as forest fuel and terrain features are relatively rare, due to a lack of spatial data sets and spatial analysis technology. Thus, the aim of this study was to identify the key climatic and non-climatic factors driving lightning-induced fires in the Tahe area using fire occurrence and metrological data along with digital forest maps in conjunction with logistic regression models and spatial analysis. Fire occurrence data included location, time, and area burned of lightning-induced fires in the Tahe region, Daxing''an Mountains, 1974-2009. Meteorological data were daily minimum temperature, daily maximum temperature, maximum wind speed, 24 hour precipitation, average air pressure, average wind speed, average relative humidity, sunshine hours, and minimum relative humidity. In addition, we calculated the Fine Fuel Moisture Code (FFMC), Duff Moisture Code (DMC) and Drought Code (DC) according to the Canadian forest Fire Weather Index (FWI). In this study, 1:100000 digital geographic and forest maps of the Tahe region were used to extract elevation, slope, aspect, depth of humus layer, litter cover, forest type, management regime, dominant tree, age class and canopy data in order to determine the factors driving lightning-induced fire occurrence in the study area. A logistic regression model was developed to examine the relationship between lighting-induced fire, and climatic and non-climate factors. The spatial distribution of lighting-induce fires was analyzed using ArcGIS10.0. Three climate factors (Daily minimum temperature, maximum wind speed and minimum relative humidity) and two fuel indices (FFMC and DC) were significantly associated with lightning-induced fires (P < 0.05), and the goodness-of-fit of the model was R² = 0.326. Moreover, litter cover and tree age class were significantly related to the occurrence of lightning-induced fires, albeit with low R² (0.15). A map of fire likelihood was created using Kriging interpolation in ArcGIS, and the spatial coordinates of lightning-induced fires (1974-2005) along with the same number of random control points. This identified four high lightning-induced fire-risk regions in our study area, which are located in the middle and South of the Tahe area. In conclusion, the results from this study provide evidence that the consideration of not only climatic, but also fuel and non-climatic factors, is critical for understanding and predicting the occurrence of lightning-induced fires in the Tahe area.