Abstract. Live fuel moisture content (LFMC) plays a critical role in wildfire dynamics, but little is known about responses of LFMC to multivariate climate change, e.g., warming temperature, CO₂ fertilization and altered precipitation patterns, leading to a limited prediction ability of future wildfire risks. Here, we use a hydrodynamic vegetation model to estimate LFMC dynamics of chaparral shrubs, a dominant vegetation type in fire-prone southern California. We parameterize the model based on observed shrub allometry and hydraulic traits, and evaluate the model's accuracy through comparisons between simulated and observed LFMC of three plant functional types (PFTs) under current climate conditions. Moreover, we estimate the number of days per year of LFMC below 79 % (which is a critical threshold for wildfire danger rating) from 1950 to 2099 for each PFT, and compare the number of days below the threshold for medium and high greenhouse gas emission scenarios (RCP4.5 and 8.5). We find that climate change could lead to more days per year (5.5–15.2 % increase) with LFMC below 79 % from historical period 1950–1999 to future period 2075–2099, and therefore cause an increase in wildlife danger for chaparral shrubs in southern California. Under the high greenhouse gas emission scenario during the dry season, we find that the future LFMC reductions mainly result from a warming temperature, which leads to 9.5–19.1 % reduction in LFMC. Lower precipitation in the spring leads to a 6.6–8.3 % reduction in LFMC. The combined impacts of warming and precipitation change on fire season length are equal to the additive impacts of warming and precipitation change individually. Our results show that the CO₂ fertilization will mitigate fire risk by causing a 3.7–5.1 % increase in LFMC. Our results suggest that multivariate climate change could cause a significant net reduction in LFMC and thus exacerbate future wildfire danger in chaparral shrub systems.

中文翻译：

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使用水动力植被模型评估气候变化对生活燃料水分和野火风险的影响

摘要。活燃料水分含量（LFMC）在野火动态中起着至关重要的作用，但是人们对LFMC对多元气候变化（例如变暖温度，CO _2）的响应知之甚少。施肥和降雨模式的变化，导致未来野火风险的预测能力有限。在这里，我们使用水动力植被模型来估算林冠灌木的LFMC动态，该灌木林是易发火灾的南加州的主要植被类型。我们基于观测到的灌木丛异构性和水力特征对模型进行参数化，并通过在当前气候条件下对三种植物功能类型（PFT）的模拟和观测到的LFMC进行比较来评估模型的准确性。此外，我们估算了每个PFT从1950年到2099年LFMC每年低于79％（这是野火危险等级的关键阈值）的天数，并比较低于中高温室气体排放阈值的天数场景（RCP4.5和8.5）。我们发现，从1950年至1999年的历史时期到2075年至2099年的未来时期，气候变化可能导致LFMC低于79％的情况下，每年导致更多的日子（增加5.5-15.2％），因此导致南部地区丛林灌木的野生生物危险性增加加利福尼亚 在干旱季节温室气体排放量较高的情况下，我们发现未来的LFMC降低主要是由于温度升高，导致LFMC降低9.5-19.1％。春季降水减少导致LFMC降低6.6–8.3％。变暖和降水变化对火季长度的综合影响等于变暖和降水变化单独的累加影响。我们的结果表明，CO 因此，在加利福尼亚州南部，野生生物增加了丛林灌木的危险。在干旱季节温室气体排放量较高的情况下，我们发现未来的LFMC降低主要是由于温度升高，导致LFMC降低9.5-19.1％。春季降水减少导致LFMC降低6.6–8.3％。变暖和降水变化对火季长度的综合影响等于变暖和降水变化单独的累加影响。我们的结果表明，CO 因此，在加利福尼亚州南部，野生生物增加了丛林灌木的危险。在干旱季节温室气体排放量较高的情况下，我们发现未来的LFMC降低主要是由于温度升高，导致LFMC降低9.5-19.1％。春季降水减少导致LFMC降低6.6–8.3％。变暖和降水变化对火季长度的综合影响等于变暖和降水变化单独的累加影响。我们的结果表明，CO 春季降水减少导致LFMC降低6.6–8.3％。变暖和降水变化对火季长度的综合影响等于变暖和降水变化单独的累加影响。我们的结果表明，CO 春季降水减少导致LFMC降低6.6–8.3％。变暖和降水变化对火季长度的综合影响等于变暖和降水变化单独的累加影响。我们的结果表明，CO₂施肥将导致LFMC增加3.7–5.1％，从而减轻火灾风险。我们的结果表明，多变量的气候变化可能会导致LFMC的净减少量显着减少，从而加剧未来丛林灌木系统的野火危险。