Department of Forest Ecosystems, and Society, Oregon State University, Corvallis, Oregon.
SLevis Consulting, LLC, Oceanside, California.
Glob Chang Biol. 2019 Jan;25(1):290-303. doi: 10.1111/gcb.14490. Epub 2018 Nov 15.
Recent prolonged droughts and catastrophic wildfires in the western United States have raised concerns about the potential for forest mortality to impact forest structure, forest ecosystem services, and the economic vitality of communities in the coming decades. We used the Community Land Model (CLM) to determine forest vulnerability to mortality from drought and fire by the year 2049. We modified CLM to represent 13 major forest types in the western United States and ran simulations at a 4-km grid resolution, driven with climate projections from two general circulation models under one emissions scenario (RCP 8.5). We developed metrics of vulnerability to short-term extreme and prolonged drought based on annual allocation to stem growth and net primary productivity. We calculated fire vulnerability based on changes in simulated future area burned relative to historical area burned. Simulated historical drought vulnerability was medium to high in areas with observations of recent drought-related mortality. Comparisons of observed and simulated historical area burned indicate simulated future fire vulnerability could be underestimated by 3% in the Sierra Nevada and overestimated by 3% in the Rocky Mountains. Projections show that water-limited forests in the Rocky Mountains, Southwest, and Great Basin regions will be the most vulnerable to future drought-related mortality, and vulnerability to future fire will be highest in the Sierra Nevada and portions of the Rocky Mountains. High carbon-density forests in the Pacific coast and western Cascades regions are projected to be the least vulnerable to either drought or fire. Importantly, differences in climate projections lead to only 1% of the domain with conflicting low and high vulnerability to fire and no area with conflicting drought vulnerability. Our drought vulnerability metrics could be incorporated as probabilistic mortality rates in earth system models, enabling more robust estimates of the feedbacks between the land and atmosphere over the 21st century.
近年来，美国西部持续的长时间干旱和灾难性野火引发了人们对未来几十年森林死亡率可能影响森林结构、森林生态系统服务以及社区经济活力的担忧。我们使用了社区土地模型（CLM）来确定森林对干旱和火灾死亡率的脆弱性，预计这一情况将在 2049 年出现。我们对 CLM 进行了修改，以代表美国西部的 13 种主要森林类型，并在 4 公里的网格分辨率下进行了模拟，驱动因素是两个大气环流模型在一种排放情景（RCP8.5）下的气候预测。我们根据茎生长和净初级生产力的年分配来制定短期极端干旱和长期干旱脆弱性的指标。我们根据模拟未来面积燃烧相对于历史面积燃烧的变化来计算火灾脆弱性。模拟的历史干旱脆弱性在有近期干旱相关死亡率观测的地区为中等到高。对观测和模拟历史时期的火灾面积的比较表明，模拟未来的火灾脆弱性在内华达山脉可能低估了 3%，在落基山脉可能高估了 3%。预测显示，落基山脉、西南部和大盆地地区的水分限制森林将最容易受到未来与干旱相关的死亡率的影响，而在内华达山脉和落基山脉的部分地区，未来火灾的脆弱性将最高。太平洋沿岸和西部喀斯喀特山脉地区的高碳密度森林预计对干旱或火灾的脆弱性最低。重要的是，气候预测的差异仅导致 1%的区域存在对火灾脆弱性的低和高的冲突，没有任何区域存在对干旱脆弱性的冲突。我们的干旱脆弱性指标可以作为概率死亡率纳入地球系统模型，从而更准确地估计 21 世纪陆地和大气之间的反馈。
