厄尔尼诺/拉尼娜对大兴安岭森林火险天气的影响

Impacts of El Nio/La Nia on Fire Weather of Daxing'anling

[目的]通过研究厄尔尼诺/拉尼娜事件对大兴安岭天气和火天气指数的影响,定量描述厄尔尼诺/拉尼娜事件在火天气指数变化中的作用。[方法]根据研究区及周边气象站日最高气温、日最小相对湿度、平均风速和24 h降水量计算1951—2016年大兴安岭森林火险天气指数,分析超强和强厄尔尼诺年、中等和弱厄尔尼诺年、拉尼娜年和正常年等4种情景下的主要天气因子和火天气指数的差异。[结果]春季火险期,超强和强厄尔尼诺年日均最高气温较正常年偏低0. 21℃,降水量增加6. 78%,拉尼娜年日均最高气温增加0. 44℃,降水量增加2. 77 mm;厄尔尼诺/拉尼娜年的秋季火险期日均最高气温低于正常年。超强和强厄尔尼诺年春季和秋季火险期的细小可燃物湿度码(FFMC)、腐殖质湿度码(DMC)、干旱码(DC)、累积指数(BUI)和火天气指数(FWI)平均值低于正常年份,FWI从西南到东北逐渐降低;中等和弱厄尔尼诺年春季火险期6个指数均低于正常年份,秋季火险期除FFMC外其他火天气指数均低于正常年份;拉尼娜年春季火险期的FFMC、初始蔓延速度(ISI)和FWI低于正常年份,秋季火险期除DC外其他指数均低于正常年份。[结论]大兴安岭地区在超强和强厄尔尼诺年春秋季火险期火天气指数较正常年份低,西部地区火天气指数高于东部地区。拉尼娜年春季火险期东部地区FWI低于正常年份,中西部偏高,秋季火险期西北部地区高于正常年份,东南部偏低。

[Objective]To Study the impacts of the El Nino/La Nina events on the fire weather of Daxing’anling so as to improve the accuracy of fire danger forecasting.[Method]The values of fire weather index during 1951-2016 were calculated including the daily maximum temperature,the minimum relative humidity,the average wind speed,and the 24-hour precipitation collected by weather stations in the study area,and the differences of the weather and fire weather indices under four scenarios of the super strong and strong El Nino,moderate and weak El Nino,La Nina and normal years were analyzed respectively.[Result]Compared with the normal year,the average daily maximum temperature in the spring fire season in super strong and strong El Nino years decreased by 0.21℃,and precipitation increased by 6.78%.In spring fire season of La Nina years,the average daily maximum temperature was 0.44℃higher,and the precipitation increased by 2.77mm.The daily maximum temperature of autumn fire season in El Nino/La Nina years was lower than that of the normal years.The average of fine fuel moisture code(FFMC),duff moisture code(DMC),drought code(DC),build up index(BUI)and fire weather index(FWI)in spring and autumn fire season under the situations of super strong and strong El Nino event were lower than those in normal years,and the FWI gradually decreased from southwest to Northeast.All six component fire weather indices of spring fire season in moderate and weak El Nino years were lower than those in normal years and also lower in autumn fire season except FFMC.In La Nina years,the FFMC,the initial spread index(ISI)and the FWI of spring fire season were lower than those of normal years,and all the indexes were lower than those in normal years as well,except for DC.[Conclusion]The forest fire weather index of super strong and strong El Nino in spring and autumn fire season was lower than that of the normal years in Daxing’anling,and the index of the western region was higher than that in the eastern region.In La Nina year,The FWI in spring fire season in the eastern region was lower than normal years and higher in the midwest.The FWI was higher than the normal years in northwest region and lower in southeastern in autumn fire season.