Morgan Penelope, Heyerdahl Emily K, Gibson Carly E
Department of Forest Resources, University of Idaho, Moscow, Idaho 83844-1133, USA.
Ecology. 2008 Mar;89(3):717-28. doi: 10.1890/06-2049.1.
We inferred climate drivers of 20th-century years with regionally synchronous forest fires in the U.S. northern Rockies. We derived annual fire extent from an existing fire atlas that includes 5038 fire polygons recorded from 12,070,086 ha, or 71% of the forested land in Idaho and Montana west of the Continental Divide. The 11 regional-fire years, those exceeding the 90th percentile in annual fire extent from 1900 to 2003 (>102,314 ha or approximately 1% of the fire atlas recording area), were concentrated early and late in the century (six from 1900 to 1934 and five from 1988 to 2003). During both periods, regional-fire years were ones when warm springs were followed by warm, dry summers and also when the Pacific Decadal Oscillation (PDO) was positive. Spring snowpack was likely reduced during warm springs and when PDO was positive, resulting in longer fire seasons. Regional-fire years did not vary with El Niño-Southern Oscillation (ENSO) or with climate in antecedent years. The long mid-20th century period lacking regional-fire years (1935-1987) had generally cool springs, generally negative PDO, and a lack of extremely dry summers; also, this was a period of active fire suppression. The climate drivers of regionally synchronous fire that we inferred are congruent with those of previous centuries in this region, suggesting a strong influence of spring and summer climate on fire activity throughout the 20th century despite major land-use change and fire suppression efforts. The relatively cool, moist climate during the mid-century gap in regional-fire years likely contributed to the success of fire suppression during that period. In every regional-fire year, fires burned across a range of vegetation types. Given our results and the projections for warmer springs and continued warm, dry summers, forests of the U.S. northern Rockies are likely to experience synchronous, large fires in the future.
我们推断了美国北落基山脉地区20世纪与区域同步森林火灾相关的气候驱动因素。我们从现有的火灾地图集得出年度火灾范围，该地图集包含从12,070,086公顷（即大陆分水岭以西爱达荷州和蒙大拿州71%的林地）记录的5038个火灾多边形。11个区域火灾年份（即1900年至2003年年火灾范围超过第90百分位数的年份，超过102,314公顷或约占火灾地图集记录面积的1%）集中在本世纪初和后期（1900年至1934年有6个，1988年至2003年有5个）。在这两个时期，区域火灾年份的特点是春季温暖，随后是温暖干燥的夏季，并且太平洋年代际振荡（PDO）为正。在温暖的春季以及PDO为正时，春季积雪可能减少，从而导致火灾季节延长。区域火灾年份与厄尔尼诺 - 南方涛动（ENSO）或前几年的气候无关。20世纪中叶缺乏区域火灾年份的时期（1935年至1987年）通常春季凉爽，PDO总体为负，且没有极端干燥的夏季；此外，这也是积极进行火灾扑救的时期。我们推断的区域同步火灾的气候驱动因素与该地区前几个世纪的情况一致，这表明尽管有重大的土地利用变化和火灾扑救努力，但整个20世纪春季和夏季气候对火灾活动仍有强烈影响。区域火灾年份中期相对凉爽潮湿的气候可能促成了该时期火灾扑救的成功。在每个区域火灾年份，火灾烧毁了一系列植被类型。鉴于我们的研究结果以及春季变暖、夏季持续温暖干燥的预测，美国北落基山脉的森林未来可能会经历同步的大型火灾。
