AIM: Over the past several decades, wildfires have become larger, more frequent, and/or more severe in many areas. Simultaneously, anthropogenic ignitions are steadily growing. We have little understanding of how increasing anthropogenic ignitions are changing modern fire regimes. LOCATION: Conterminous United States. TIME PERIOD: 1984–2016. MAJOR TAXA STUDIED: Vegetation. METHODS: We aggregated fire radiative power (FRP)‐based fire intensity, event size, burned area, frequency, season length, and ignition type data from > 1.8 million government records and remote sensing data at a 50‐km resolution. We evaluated the relationship between fire physical characteristics and ignition type to determine if and how modern U.S.A. fire regimes are changing sensu stricto given increased anthropogenic ignitions, and how those patterns vary over space and time. RESULTS: At a national scale, wildfires occur over longer fire seasons (17% increase) and have become larger (78%) and more frequent (12%), but not necessarily more intense. Further, human ignitions have increased 9% proportionally. The proportion of human ignitions has a negative relationship with fire size and FRP and a positive relationship with fire frequency and season length. Areas dominated by lightning ignitions experience fires that are 2.4 times more intense and 9.2 times larger. Areas dominated by human ignitions experience fires that are twice as frequent and have a fire season that is 2.4 times longer. The effect of human ignitions on fire characteristics varies regionally. Ecoregions in the eastern U.S.A. and in some parts of the coastal western U.S.A. have no areas dominated by lightning ignitions. For the remaining ecoregions, more intense and larger fires are associated with lightning ignitions, and longer season lengths are associated with human ignitions. MAIN CONCLUSIONS: Increasing anthropogenic ignitions – in tandem with climate and land cover change – are contributing to a ‘new normal’ of fire activity across continental scales.

中文翻译：

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在美国，人为和闪电引发的火灾在更长的季节长度内变得更大和更频繁

目标：在过去的几十年里，许多地区的野火变得更大、更频繁和/或更严重。与此同时，人为点火正在稳步增长。我们对日益增加的人为点火如何改变现代火灾状况知之甚少。地点：美国本土。时间段：1984-2016。研究的主要分类群：植被。方法：我们从超过 180 万份政府记录和 50 公里分辨率的遥感数据中汇总了基于火灾辐射功率 (FRP) 的火灾强度、事件规模、燃烧面积、频率、季节长度和点火类型数据。我们评估了火灾物理特性和点火类型之间的关系，以确定现代美国火灾制度是否以及如何在人为点火增加的情况下改变严格意义上的点火，以及这些模式如何随空间和时间变化。结果：在全国范围内，野火发生在更长的火灾季节（增加 17%）并且变得更大（78%）和更频繁（12%），但不一定更强烈。此外，人类点火按比例增加了 9%。人为点火的比例与火灾大小和 FRP 呈负相关，与火灾频率和季节长度呈正相关。以闪电点火为主的区域的火灾强度是其 2.4 倍和 9.2 倍。以人类点火为主的地区发生火灾的频率是其两倍，火灾季节是其 2.4 倍。人为点火对火灾特性的影响因地区而异。美国东部和美国西部沿海部分地区的生态区 没有以闪电点火为主的区域。对于其余生态区，更强烈和更大的火灾与闪电点火有关，而更长的季节长度与人类点火有关。主要结论：随着气候和土地覆盖的变化，人为点火的增加正在促成跨大陆尺度的火灾活动的“新常态”。