Unprecedentedly large areas were burned during the 2016/17 and 2022/23 fire seasons in south-central Chile (34-39°S). These seasonal-aggregated values were mostly accounted for human-caused wildfires within a limited period in late January 2017 and early February 2023. In this paper, we provide a comprehensive analysis of the meteorological conditions during these events, from local to hemispheric scales, and formally assess the contribution of climate change to their occurrence. To achieve this, we gathered monthly fire data from the Chilean Forestry Corporation and daily burned area estimates from satellite sources. In-situ and gridded data provided near-surface atmospheric insights, ERA5 reanalysis helped analyze broader wildfire features, high-resolution simulations were used to obtain details of the wind field, and large-ensemble simulations allowed the assessment of climate change's impact on extreme temperatures during the fires. This study found extraordinary daily burned area values (>65,000 ha) occurring under extreme surface weather conditions (temperature, humidity, and winds), fostered by strong mid-level subsidence ahead of a ridge and downslope winds converging towards a coastal low. Daytime temperatures and the water vapor deficit reached the maximum values observed across the region, well above the previous historical records. We hypothesize that these conditions were crucial in exacerbating the spread of fire, along with longer-term atmospheric processes and other non-climatic factors such as fuel availability and increasing human-driven ignitions. Our findings further reveal that climate change has increased the probability and intensity of extremely warm temperatures in south-central Chile, underscoring anthropogenic forcing as a significant driver of the extreme fire activity in the region.

中文翻译：

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极端天气和气候变化在智利中南部异常火灾季节发生中的关键作用


2016/17 和 2022/23 火灾季节，智利中南部（南纬 34-39°）发生了前所未有的大面积烧毁。这些季节性汇总值主要是2017年1月下旬至2023年2月上旬有限时间内人为造成的野火。在本文中，我们对这些事件期间的气象条件（从局地到半球尺度）进行了全面分析，并正式评估气候变化对其发生的影响。为了实现这一目标，我们从智利林业公司收集了每月火灾数据，并从卫星来源收集了每日燃烧面积估计值。现场和网格数据提供了近地表大气洞察，ERA5再分析有助于分析更广泛的野火特征，高分辨率模拟用于获取风场的详细信息，大型集合模拟可以评估气候变化对极端温度的影响在火灾期间。这项研究发现，在极端地表天气条件（温度、湿度和风）下，日烧面积值（>65,000 公顷）出现异常，这是由山脊前的强烈中层沉降和向沿海低压汇聚的下坡风促成的。白天气温和水汽不足达到了该地区观测到的最大值，远高于之前的历史记录。我们假设这些条件以及长期大气过程和其他非气候因素（例如燃料可用性和人为点火增加）对于加剧火势蔓延至关重要。 我们的研究结果进一步表明，气候变化增加了智利中南部极端高温的可能性和强度，强调人为强迫是该地区极端火灾活动的重要驱动因素。