大兴安岭雷击火时空分布及预报模型

Spatial and Temporal Distribution of Lightning Fire and Forecasting Model for Daxing'anling Region

雷击火是中国大兴安岭地区重要火源。根据1990--200年研究区内10个气象站日观测数据包括最高气温、最小湿度、24h降水、平均风速等指标计算每日FWI系统各指标，分析雷击火的发生与火险指数的关系。根据各气象站与研究区质心的距离确定各气象站的权重，计算研究区火险指数平均值。1990-2006年大兴安岭林区共发生森林火灾591起，其中雷击火359起，占60．7％。70％的雷击火分布在121°～125°E，51°～53°N，平均每起雷击火过火面积为797．37hm^2，森林受害面积为581．67hm^2。71．9％、2．5％和17．3％的雷击火分别发生在落叶针叶林、落叶阔叶林和草地。雷击火发生在4—9月，5—8月是雷击火多发月份。1990-2006年雷击火发生时间段整体上有延长趋势。8月和9月发生的雷击火都发生在1998-2005年。雷击火的发生受气温与降水的影响，月均气温高、降水量少，雷击火次数明显多。发生雷击火日的平均可燃物湿度码FFMC、DMC、DC和FWI分别为90．3，69．6，287．4和24．7。雷击火发生日各火险成分指数平均值均高于1990-2006年4—9月总体平均值。根据雷击火发生概率和每日火险指数建立了雷击火发生概率预测模型。

Lightning is an important fire source in Daxing＇anling region, China （119.60°--127.02° E, 47.05°-- 53.56° N） . The daily fire weather index （FWI） component indexes were calculated based on the observations of 10 weather stations in the study area from 1990--2006. The observations of weather station included daily maximum temperature, daily minimum humidity, precipitation in 24-hour （20 ： 00--20：00） , and average wind speed. The weights of weather stations were determined according to the distances between each weather station and the study area center （122.665 5° E, 51. 013 7° N）. Then the averages of FWI component indexes were calculated for the study area for analyzing its relationship with lightning fire occurrence. There were 591 wildfires in the Daxing＇anling region from 1990--2006, in which 359 lightning fires accounting for 60.7 percent. 70% of lightning fires distribute in the area 121°--125° E, 51°--53° N. The average burned area of each lightning fire was 797.37 hm^2, and burned forest 581.67 hm^2. Lightning fires occurred in the deciduous conifer forest, deciduous broad-leaved forest and grassland accounted for 71.9%, 2.5% and 17.3% respectively. Lightning fires occurred in the period from April to September and mainly in May to August. June was the month with most lightning fire （105 fires） from 1990--2006, which accounted for 29.7%. It was followed by July, 28.3% lightning fires. During 1990--2006, the lightning fire season got longer in overall. From 1990--1998, lightning fires occurred in the period from April 24 to July 26, but in 1998--2006 lightning fire season extended to the end of September. All lightning fires occurred in August and September were the years from 1998--2005. Air temperature and precipitation influenced on lightning fire occurrence. In a higher month-average of daily maximum temperatures and less month-precipitation, lightning fires will increased significantly. Month-averages of fine fuel moisture code （ FFMC）, duff moisture code （ DMC）, drought code （DC） and FWI in dates from April to September when lightning fire occurred were 90.3, 69.6, 287.4 and 24.7 respectively, which were higher than those averages from 1990--2006. A probability forecasting model of lightning fire was established on the base of lightning fire occurrence probability and daily fire weather index.