Human-started wildfires expand the fire niche across the United States.
Human-started wildfires expand the fire niche across the United States.
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DOI：
10.1073/pnas.1617394114
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发表时间：
2017-03-14
影响因子：
11.1
通讯作者：
Mahood AL
中科院分区：
文献类型：
--
作者：
Balch JK;Bradley BA;Abatzoglou JT;Nagy RC;Fusco EJ;Mahood AL
在美国，扑灭野火每年花费数十亿美元。公众对话和正在进行的研究集中在由于气候变暖而增加的野火风险上，忽视了人们在点燃野火和增加火灾活动中发挥的直接作用。我们对二十年来政府机构野火记录的分析突出了人类点火的基本作用。人类引发的野火占所有野火的84%，是火灾季节长度的三倍，占比闪电火灾影响面积的七倍，并且占所有烧毁面积的近一半。国家和区域减轻野火相关危害的政策努力将受益于侧重于减少人类对火灾生态位的扩张。近几十年来，美国野火的经济和生态成本大幅上升。虽然气候变化可能导致了野火活动的部分增加，但人们在野火活动增加中的直接作用在很大程度上被忽视了。我们评估了1992年至2012年期间由州或联邦机构扑灭或管理的150多万份政府野火记录，并检查了人类点燃的野火相对于闪电点燃的野火的地理和季节范围。人类极大地扩展了美国境内的空间和季节性“火生态位”，占所有野火的84%，占总烧毁面积的44%。在这21年的时间里，人为火灾季节是闪电火灾季节的三倍，平均每年在美国增加4万起野火。人类引发的野火通常发生在燃料湿度高于闪电引发的火灾的地方，从而有助于扩大野火的地理和季节性生态位。人类引发的野火在美国绝大多数地区超过510万平方公里的地区占主导地位（>80%的点火），而闪电引发的火灾仅在70万平方公里的地区占主导地位，主要是在美国西部山区人口稀少的地区。人类活动引起的火灾是生态系统和经济面临的总体火灾风险的一个重要驱动因素。在容易发生人为野火的地区采取行动提高认识和加强管理，应成为美国减少火灾风险和相关危害的政策重点。
Fighting wildfires in the United States costs billions of dollars annually. Public dialog and ongoing research have focused on increasing wildfire risk because of climate warming, overlooking the direct role that people play in igniting wildfires and increasing fire activity. Our analysis of two decades of government agency wildfire records highlights the fundamental role of human ignitions. Human-started wildfires accounted for 84% of all wildfires, tripled the length of the fire season, dominated an area seven times greater than that affected by lightning fires, and were responsible for nearly half of all area burned. National and regional policy efforts to mitigate wildfire-related hazards would benefit from focusing on reducing the human expansion of the fire niche. The economic and ecological costs of wildfire in the United States have risen substantially in recent decades. Although climate change has likely enabled a portion of the increase in wildfire activity, the direct role of people in increasing wildfire activity has been largely overlooked. We evaluate over 1.5 million government records of wildfires that had to be extinguished or managed by state or federal agencies from 1992 to 2012, and examined geographic and seasonal extents of human-ignited wildfires relative to lightning-ignited wildfires. Humans have vastly expanded the spatial and seasonal “fire niche” in the coterminous United States, accounting for 84% of all wildfires and 44% of total area burned. During the 21-y time period, the human-caused fire season was three times longer than the lightning-caused fire season and added an average of 40,000 wildfires per year across the United States. Human-started wildfires disproportionally occurred where fuel moisture was higher than lightning-started fires, thereby helping expand the geographic and seasonal niche of wildfire. Human-started wildfires were dominant (>80% of ignitions) in over 5.1 million km2, the vast majority of the United States, whereas lightning-started fires were dominant in only 0.7 million km2, primarily in sparsely populated areas of the mountainous western United States. Ignitions caused by human activities are a substantial driver of overall fire risk to ecosystems and economies. Actions to raise awareness and increase management in regions prone to human-started wildfires should be a focus of United States policy to reduce fire risk and associated hazards.