Temporal and spatial pattern analysis of escaped prescribed fires in California from 1991 to 2020

Prescribed fires play a critical role in reducing the intensity and severity of future wildfires by systematically and widely consuming accumulated vegetation fuel. While the current probability of prescribed fire escape in the United States stands very low, its consequential impact, particularly the large wildfires it causes, raises substantial concerns. The most direct way of understanding this trade-off between wildfire risk reduction and prescribed fire escapes is to explore patterns in the historical prescribed fire records. This study investigates the spatiotemporal patterns of escaped prescribed fires in California from 1991 to 2020, offering insights for resource managers in developing effective forest management and fuel treatment strategies. The results reveal that the months close to the beginning and end of the wildfire season, namely May, June, September, and November, have the highest frequency of escaped fires. Under similar environmental conditions, areas with more records of prescribed fire implementation tend to experience fewer escapes. The findings revealed the vegetation types most susceptible to escaped prescribed fires. Areas with tree cover ranging from 20 to 60% exhibited the highest incidence of escapes compared to shrubs and grasslands. Among all the environmental conditions analyzed, wind speed stands out as the predominant factor that affects the risk of prescribed fire escaping. These findings mark an initial step in identifying high-risk areas and periods for prescribed fire escapes. Understanding these patterns and the challenges of quantifying escape rates can inform more effective landscape management practices.

计划火烧（prescribed fire）通过系统性、大范围地消耗累积的森林植被可燃物，在降低未来野火（wildfire）的强度与烈度方面发挥关键作用。目前美国境内计划火烧脱逃的概率极低，但其所引发的严重后果——尤其是由此催生的大型野火——仍引发了广泛担忧。理解野火风险削减与计划火烧脱逃之间权衡关系的最直接途径，便是探究历史计划火烧记录中的规律模式。
本研究针对1991年至2020年加利福尼亚州境内脱逃型计划火烧的时空分布特征展开调查，可为森林资源管理人员制定高效的森林管理与可燃物处理策略提供参考依据。研究结果显示，接近野火季始末的月份——即5月、6月、9月与11月——的脱逃火烧发生频率最高。在相似环境条件下，计划火烧实施记录更多的区域，脱逃事件的发生概率往往更低。本研究明确了最易发生计划火烧脱逃的植被类型：相较于灌丛与草原，林木覆盖率介于20%至60%的区域脱逃事件发生率最高。在所有分析的环境因素中，风速是影响计划火烧脱逃风险的主导因子。
上述研究成果为识别计划火烧脱逃的高风险区域与时段迈出了初步探索的一步。明晰此类规律以及量化脱逃率面临的挑战，可为更高效的景观管理实践提供决策支持。