Thermokarst acceleration in Arctic tundra driven by climate change and fire disturbance, 1950-2015

Climate warming is projected to intensify tundra wildfire, with profound implications for permafrost thaw. A major uncertainty is how increased burning will interact with climate change to exacerbate thermokarst (ground-surface collapse resulting from permafrost thaw). Here we used ~70 years of remote sensing observation combined with spatially-explicit modeling to show that thermokarst rates increased by ~60% with warming climate and wildfire from 1950 to 2015 in Arctic Alaska. Wildfire amplified thermokarst over 40+ years, cumulatively creating ~9 times thermokarst formation as that in unburned tundra. However, thermokarst triggered by repeat burns did not differ from that triggered by single burns, irrespective of time between fires. Our simulation identified climate change as a principal driver for all thermokarst formed during 1950-2015 (4,700 square kilometers (km2)) in Arctic Alaska, but wildfire was disproportionately responsible for 10.5% of the thermokarst by burning merely 3.4% of the landscape. These results combined suggest that climate change and wildfire will synergistically accelerate thermokarst as the Arctic transitions in this century.

据预测，气候变暖将加剧苔原（tundra）野火的发生，这对多年冻土（permafrost）融化具有深远影响。当前一项核心不确定性在于，野火频次增加将如何与气候变化相互作用，进而加剧热喀斯特（thermokarst，即由多年冻土融化引发的地表塌陷）的发育。本研究结合近70年的遥感观测数据与空间显式建模（spatially-explicit modeling）方法，结果显示，1950年至2015年间，阿拉斯加北极地区的热喀斯特发育速率因气候变暖和野火活动提升了约60%。在超过40年的时间尺度上，野火显著放大了热喀斯特的发育程度，其累计形成的热喀斯特规模约为未受野火干扰苔原的9倍。然而，无论两次野火之间的间隔时长如何，重复火烧引发的热喀斯特发育程度与单次火烧并无显著差异。本研究的模拟结果表明，气候变化是阿拉斯加北极地区1950-2015年间所有热喀斯特（总面积达4700平方千米）形成的主要驱动因素，但野火仅燃烧了该区域3.4%的地表，却促成了总计10.5%的热喀斯特发育，其贡献比例远超其燃烧面积占比。综合上述结果可知，随着本世纪北极地区发生气候转型，气候变化与野火活动将协同加速热喀斯特的发育。