Data and code from: Shifting social-ecological fire regimes explain increasing structure loss from Western wildfires

Higuera, P.E., M.C. Cook, J.K. Balch, E.N. Stavros, A.L. Mahood, and L.A. St. Denis. 2023. Shifting social-ecological fire regimes explain increasing structure loss from Western wildfires. PNAS Nexus 2: In Press.

Structure loss is an acute, costly impact of the wildfire crisis in the western United States (“West”), motivating the need to understand recent trends and causes. We document a 246% rise in West-wide structure loss from wildfires between 1999–2009 and 2010–2020, driven strongly by events in 2017, 2018, and 2020. Increased structure loss was not due to increased area burned alone. Wildfires became significantly more destructive, with a 160% higher structure loss rate (loss/kha burned) over the past decade. Structure loss was driven primarily by wildfires from unplanned human-related ignitions (e.g. backyard burning, power lines, etc.), which accounted for 76% of all structure loss and resulted in 10 times more structures destroyed per unit area burned compared to lightning-ignited fires. Annual structure loss was well explained by area burned from human-related ignitions, while decadal structure loss was explained by state-level structure abundance in flammable vegetation. Both predictors increased over recent decades and likely interacted with increased fuel aridity to drive structure-loss trends. While states are diverse in patterns and trends, nearly all experienced more burning from human-related ignitions and/or higher structure loss rates, particularly California, Washington, and Oregon. Our findings highlight how fire regimes – characteristics of fire over space and time – are fundamentally social-ecological phenomena. By resolving the diversity of Western fire regimes, our work informs regionally appropriate mitigation and adaptation strategies. With millions of structures with high fire risk, reducing human-related ignitions and rethinking how we build are critical for preventing future wildfire disasters.

Methods
See associated paper.

Higuera, P.E.、M.C. Cook、J.K. Balch、E.N. Stavros、A.L. Mahood 及 L.A. St. Denis 于2023年在《PNAS Nexus》第2卷待刊论文《动态变化的社会-生态火制度解释了美国西部林火引发的建筑损毁加剧现象》中指出：建筑损毁是美国西部（下称“西部”）林火危机带来的一项紧急且代价高昂的负面影响，促使学界亟需厘清近期的损毁趋势与成因。研究团队的测算显示，1999-2009年至2010-2020年间，美国西部因林火导致的建筑损毁数量增幅达246%，其中2017、2018及2020年的特大火灾对此推动作用最为显著。建筑损毁的加剧并非仅由过火面积扩张所致：近十年间，林火的破坏性显著提升，单位过火面积（每千公顷，kha）的建筑损毁率上升160%。

建筑损毁主要由人为非计划性火源引发的林火驱动（例如后院焚烧、输电线路故障等），此类火灾占总建筑损毁事件的76%，且每单位过火面积损毁的建筑数量是雷击引发林火的10倍。年度建筑损毁情况可通过人为火源的过火面积得到良好解释，而年代际建筑损毁则与可燃植被区域内各州的建筑存量密切相关。上述两类影响因子在近几十年来均呈上升趋势，且可能与燃料干旱度升高共同作用，推动了建筑损毁的变化趋势。

尽管各州的火灾模式与变化趋势存在显著差异，但几乎所有州均出现了人为火源过火面积增加和/或建筑损毁率上升的情况，其中加利福尼亚州、华盛顿州与俄勒冈州尤为突出。本研究结果凸显了火制度（fire regime）——即火灾在时空维度上的整体特征——本质上属于社会-生态现象。通过厘清美国西部火制度的多样性，本研究可为制定适配区域的减灾与适应策略提供科学依据。当前有数百万栋建筑面临极高的火灾风险，减少人为火源引发的火灾并重新审视建筑建造方式，对于防范未来的林火灾害至关重要。

研究方法 详见关联论文。