Anthropogenic climate change is altering the state of worldwide fire regimes, including by increasing the number of days per year when vegetation is dry enough to burn. Indices representing the percent moisture content of dead fine fuels as derived from meteorological data have been used to assess geographic patterns and temporal trends in vegetation flammability. To date, this approach has assumed a single flammability threshold, typically between 8 and 12%, controlling fire potential regardless of the vegetation type or climate domain. Here we use remotely sensed burnt area products and a common fire weather index calculated from global meteorological reanalysis data to identify and describe geographic variation in fuel moisture as a flammability threshold. This geospatial analysis identified a wide range of flammability thresholds associated with fire activity across 772 ecoregions, often well above or below the commonly used range of values. Many boreal and temperate forests, for example, can ignite and sustain wildfires with higher estimated fuel moisture than previously identified; Mediterranean forests, in contrast, tend to sustain fires with consistently low estimated fuel moisture. Statistical modelling showed that flammability thresholds derived from burnt area are primarily driven by climatological variables, particularly precipitation and temperature. Our analysis also identified complex associations between vegetation structure, fuel types, and climatic conditions highlighting the complexity in vegetation–climate–fire relationships globally. Our study provides a critical, necessary step in understanding and describing global pyrogeography and tracking changes in spatial and temporal fire activity.

中文翻译：

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生态区可燃性阈值的全球变化


人为气候变化正在改变全球火灾状况，包括每年增加植被干燥到可以燃烧的天数。根据气象数据得出的代表死细燃料水分含量百分比的指数已用于评估植被可燃性的地理模式和时间趋势。迄今为止，该方法假设单一可燃性阈值（通常在 8% 至 12% 之间），无论植被类型或气候域如何，都可以控制火灾潜力。在这里，我们使用遥感燃烧区域产品和根据全球气象再分析数据计算出的常见火灾天气指数来识别和描述燃料湿度的地理变化作为可燃性阈值。这项地理空间分析确定了 772 个生态区域与火灾活动相关的各种可燃性阈值，这些阈值通常远高于或低于常用的值范围。例如，许多北方和温带森林可以用比之前确定的更高的估计燃料湿度点燃和维持野火；相比之下，地中海森林往往会在燃料湿度持续较低的情况下维持火灾。统计模型表明，从燃烧区域得出的可燃性阈值主要由气候变量驱动，特别是降水和温度。我们的分析还确定了植被结构、燃料类型和气候条件之间的复杂关联，凸显了全球植被-气候-火灾关系的复杂性。我们的研究为理解和描述全球火地理以及跟踪火灾活动的时空变化提供了关键、必要的一步。