基于GB/T36743-2018森林火险气象等级国家标准,分析了广西91个国家气象站1981-2020年森林火险气象等级特征,并利用林火实况进行了验证.广西高火险区位于桂西百色市、崇左市和沿海北海市,高火险期是10-12月.影响广西森林火险气象等级最主要的气象要素是降水量,其次为气温,风速和相对湿度影响较小.利用NCEP/NCAR再分析资料、NOAA海温资料和相关系数分析方法和合成分析方法,从海温和对流层中低层位势高度、风场、垂直速度和海平面气压等的异常特征对广西高火险期高火险日数差异的分析表明:关键区海温不同的海气相互作用引起的降水量差异造成了广西高火险日数的异常.秋季赤道中东太平洋冷(暖)海温激发出菲律宾异常气旋环流(南海异常反气旋环流),东亚冬季风(西南暖湿气流)偏强,副高偏弱偏东(偏强偏西),广西处于下沉干燥(上升湿润)气流区,降水偏少(多),高火险期高火险日数偏多(少).
Based on the GB/T 36743-2018 national standard for forest fire risk meteorological level,we have analyzed the characteristics of forest fire risk meteorological levels at 91 national meteorological stations in Guangxi from 1981 to 2020.We also verified our results using actual forest fire conditions.The areas with high forest fire risk are located in Baise and Chongzuo in the west of Guangxi,and Beihai in the coastal region.The average number of days with high fire risk is less in the northeast of Guangxi.The high fire risk period is from October to December,with the number of high fire risk days during this period accounting for 45.3%of the entire year.Among the four meteorological factors affecting the meteorological level of forest fire risk in Guangxi,precipitation has the greatest impact,followed by temperature.Wind speed and relative humidity have a comparatively lesser impact.We have studied the abnormal characteristics of sea surface temperature and atmospheric circulation of sea level pressure,geopotential height,wind field,and vertical velocity in the middle and lower troposphere using NCEP/NCAR monthly average reanalysis data,NOAA monthly sea surface temperature data,correlation coefficient analysis method,and composite analysis method.We also have examined the causes of the differences in the number of high fire risk days during the high forest fire risk period in Guangxi.The results reveal that the variant interactions between the ocean and the atmosphere,induced by the sea surface temperature in key areas in autumn,lead to differences in precipitation during the high fire risk period in Guangxi.This in turn results in differences in the number of high fire risk days.In autumn,the cold sea surface temperature in the equatorial Middle East Pacific triggers the abnormal cyclone circulation in the Philippines from October to December.The East Asian winter monsoon becomes stronger,and the western Pacific subtropical high is weaker than normal and shifts to the east.Consequently,Guangxi is in a sinking dry air flow area with less precipitation,leading to a higher number of high fire risk days during the high fire risk period.Conversely,the warm sea surface temperature in the equatorial Middle East Pacific in autumn gives rise to the abnormal anticyclone circulation in the South China Sea.The western Pacific subtropical high is stronger,and its ridge point extends westward.The warm and humid southwest airflow is stronger,and Guangxi is in the area of rising humid airflow.This results in more precipitation,thereby reducing the number of high fire risk days during the high fire risk period.