FireALT dataset: estimated active layer thickness for paired burned unburned sites measured from 2001-2023

As the northern high latitude permafrost zone experiences accelerated warming, permafrost has become vulnerable to widespread thaw. Simultaneously, wildfire activity across northern boreal forests and Arctic/subarctic tundra regions impacts permafrost stability through the combustion of insulating organic matter, vegetation, and post-fire changes in albedo. Despite the importance of wildfire-permafrost interactions, little research has been conducted to understand differences across ecosystem types. To address this knowledge gap, we solicited observations of active layer thickness from paired burned and unburned sites across the northern high-latitude permafrost region. We compiled 52,466 permafrost thaw depth observations from 18 contributors collected as part of individual field studies. As thaw depths were taken at various times throughout the season, we estimated end-of-season active layer thickness for each measurement using the square root of additional air thawing degree days between the day of measurement and the date of the end of the thawing season at each site. The FireALT dataset includes 48,669 ALT estimates with 32 attributes across 9,446 plots and 157 burned/unburned pairs spanning Canada, Russia, and the United States. The data were collected between 2001 and 2023 and span fire events from 1900 to 2022. Time since fire ranges from zero to 114 years. The FireALT dataset addresses a key challenge: the ability to assess the impacts of wildfire on ALT when measurements are taken at various times throughout the thaw season depending on the time of field campaigns (typically June through August) by estimating ALT at the end of the season maximum.

随着北极高纬度多年冻土区经历加速变暖，多年冻土已广泛面临大范围退化融化的风险。与此同时，北部寒温带针叶林与北极/亚北极苔原区域的野火活动，通过燃烧隔热有机质、损毁植被以及火后反照率变化，影响着多年冻土的稳定性。尽管野火与多年冻土的相互作用至关重要，但针对不同生态系统类型间差异的相关研究仍较为匮乏。
为填补这一研究空白，我们征集了北极高纬度多年冻土区成对火烧与未火烧样地的活动层厚度（active layer thickness, ALT）观测数据。我们整合了来自18家贡献方、基于独立野外研究采集的52466条多年冻土融化深度观测记录。由于融化深度的测量时间覆盖整个解冻季，我们通过计算单次测量当日与各站点解冻季结束日之间的额外空气解冻度日数的平方根，估算得到单次测量对应的季末活动层厚度。
本FireALT数据集包含48669条活动层厚度估算值，涵盖加拿大、俄罗斯与美国境内的9446个样地、157对火烧/未火烧样地，共包含32项属性指标。数据集的采集时间为2001年至2023年，覆盖的野火事件时间跨度为1900年至2022年，样地的火后时长范围为0至114年。
本数据集解决了一项关键研究难题：由于野外调查通常在6月至8月开展，解冻季内不同时段的观测数据无法直接对比，本数据集通过估算季末最大活动层厚度，实现了对野火对活动层厚度影响的科学评估。