2025年1月美国洛杉矶破纪录山火事件的干旱气象条件归因

doi:10.11755/j.issn.1006-7639-2025-05-0667

干旱气象 ›› 2025, Vol. 43 ›› Issue (5): 667-677.DOI: 10.11755/j.issn.1006-7639-2025-05-0667

• “加州山火与干旱”专栏 • 上一篇下一篇

2025年1月美国洛杉矶破纪录山火事件的干旱气象条件归因

于晓晶¹(), 张丽霞²(), 于志翔³, 杨可儿¹

1.新疆大学地理与遥感科学学院，新疆乌鲁木齐 830017
2.中国科学院大气物理研究所地球系统数值模拟与应用全国重点实验室，北京 100029
3.乌鲁木齐气象卫星地面站，新疆乌鲁木齐 830011

收稿日期:2025-08-20 修回日期:2025-09-18 出版日期:2025-10-31 发布日期:2025-11-09
通讯作者: 张丽霞（1982—），女，河北保定人，博士，研究员，主要从事极端旱涝事件发生机理及预测研究。E-mail： lixiazhang@mail.iap.ac.cn。
作者简介:于晓晶（1987—），女，山东烟台人，博士，副教授，主要从事干旱区气候变化与极端事件归因研究。E-mail： yuxj@xju.edu.cn。
基金资助:
国家自然科学基金项目(U2342228);国家自然科学基金项目(42305184);中国博士后科学基金项目(2024M752693);地球系统数值模拟装置课题(2025-EL-PT-001070);新疆维吾尔自治区“天池英才”项目

Attribution of drought-related meteorological conditions for the record-breaking wildfire event in Los Angeles in January 2025

YU Xiaojing¹(), ZHANG Lixia²(), YU Zhixiang³, YANG Ke’er¹

1. College of Geography and Remote Sensing Sciences， Xinjiang University， Urumqi 830017， China
2. State Key Laboratory of Earth System Numerical Modeling and Application， Institute of Atmospheric Physics， Chinese Academy of Sciences， Beijing 100029， China
3. Urumqi Meteorological Satellite Ground Station， Urumqi 830011， China

Received:2025-08-20 Revised:2025-09-18 Online:2025-10-31 Published:2025-11-09

摘要/Abstract

摘要：

气候增暖背景下，全球山火频率和强度呈显著上升趋势，人为活动可通过改变气候背景条件而显著加剧山火发生风险。2025年1月洛杉矶遭遇破纪录山火事件（简称“25·1”洛杉矶山火事件），前期干燥少雨的干旱状况为其发生提供了有利的气象条件，但气候自然变率和人为外强迫对此类高影响极端干旱事件的定量贡献尚未充分明晰。鉴于此，本文以“25·1”洛杉矶山火事件的关键干旱气象成因为切入点，借助中国科学院大气物理研究所极端事件检测归因系统（Detection and Attribution System of Institute of Atmospheric Physics， Chinese Academy of Sciences，CAS-DASys）开展大样本数值模拟试验并加以归因分析。观测结果表明，在“25·1”洛杉矶山火事件发生前的2024年下半年，美国西部处于持续性降水匮乏和空气干燥状况，其降水量比气候平均态（1981—2010年）偏低约60%、水汽压差（Vapor Pressure Deficit，VPD）偏高0.33 kPa；二者标准化距平分别高达为-1.83和2.13，近44 a（1981—2024年）位列第二。基于CAS-DASys模拟结果的归因分析发现，人为外强迫对美国西部降水变化影响较小，但使得VPD大幅度增加，进而导致类似2024年下半年极端干旱事件的发生。对于类似2024年的极端大气干燥状况，在自然强迫下几乎不可能发生，但在全强迫下发生概率增至0.012%（不确定性范围：0.000 46%~0.110 00%），进而极大增加了类似2024年干燥少雨状况的极端干旱事件发生概率。本研究揭示了全球增暖背景下人为外强迫对区域山火关键干旱气象因子的定量影响，可为山火气象条件的预报预测及其风险应对决策提供科学依据。

关键词: 洛杉矶山火, 极端干旱事件, 人为外强迫, 检测归因, CAS-DASys

Abstract:

Under a warming climate, the frequency and intensity of wildfires present a remarkable increasing trend globally, and human activities can significantly amplify wildfire risk by altering the wildfire-associated climate conditions. In January 2025, record-breaking wildfires swept through Los Angeles (referred to as the “25·1” Los Angeles wildfire event for short), which occurred in a favorable previous meteorological condition of scarce rainfall and atmospheric aridity. Yet, the quantitative contributions of the natural variability and human influences on such high-impact drought extremes remains unclear. Based on the Detection and Attribution System of Institute of Atmospheric Physics, Chinese Academy of Sciences (CAS-DASys), we conduct large ensemble simulations and a comprehensive attribution of the vital drought-related meteorological factors associated with the January 2025 Los Angeles wildfires. Observations show that in the second half of 2024, prior to the “25·1” Los Angeles wildfire event, the western United States was in a state of persistent lack of precipitation and dry air, and its precipitation was approximately 60% lower than the climatology (1981-2010), while the vapor pressure deficit (VPD) was 0.33 kPa higher. The standardized anomalies of these two variables reached -1.83 and 2.13, respectively, ranking the second highest in the recent 44 years (1981-2024). Attribution analysis suggests that anthropogenic forcings increase the probability of 2024-like scarce rainfall and atmospheric aridity extremes mainly by elevating the VPD in western United States, with very slight impacts on the rainfall changes. The 2024-like high VPD extremes would almost never occur under natural forcings, while the likelihood increases to 0.012% (uncertainty range: 0.000 46%-0.110 00%) under all forcings. Thus, the anthropogenic forcings largely increase the occurrence of 2024-like compound drought extremes. Our study reveals quantitative contributions of anthropogenic forcings to the key drought-related meteorological factors for regional wildfires under global warming, and provides a scientific basis for the prediction and forecasting of wildfire-associated meteorological conditions and corresponding risk prevention and decision-making.

Key words: Los Angeles wildfires, extreme drought events, anthropogenic forcings, detection and attribution, CAS-DASys

中图分类号:

P467

于晓晶, 张丽霞, 于志翔, 杨可儿. 2025年1月美国洛杉矶破纪录山火事件的干旱气象条件归因[J]. 干旱气象, 2025, 43(5): 667-677.

YU Xiaojing, ZHANG Lixia, YU Zhixiang, YANG Ke’er. Attribution of drought-related meteorological conditions for the record-breaking wildfire event in Los Angeles in January 2025[J]. Journal of Arid Meteorology, 2025, 43(5): 667-677.

图/表 9

图1 美国西部地区地形（a，单位：m）、国际地圈生物圈计划（International Geosphere Biosphere Programme，IGBP）下垫面覆盖类型（b）空间分布（三角符号表示洛杉矶位置，下同；b图中数字表示IGBP植被覆盖类型依次为：0 水，1 常绿针叶林，2 常绿阔叶林，3 落叶针叶林，4 落叶阔叶林，5 混交林，6 郁闭灌丛，7 开放灌丛，8 多树草原，9 稀树草原，10 草原，11 永久湿地，12 作物，13 城市和建成区，14 作物和自然植被的镶嵌体，15 雪、冰，16 裸地或低植被覆盖地，17 未分类区）

Fig.1 Spatial distribution of the topography of the western America (a, Unit: m) and IGBP land cover type (b) (The triangles denote the location of Los Angeles, the same as below ; The numbers for IGBP vegetation types in fig. b are as follows: 0 denotes water, 1 evergreen needleleaf forest, 2 evergreen broadleaf forest, 3 deciduous needleleaf forest, 4 deciduous broadleaf forest, 5 mixed forest, 6 closed shrubland, 7 open shrublands, 8 woody savannas, 9 savannas, 10 grasslands, 11 permanent wetlands, 12 croplands, 13 urban and built_up, 14 cropland natural vegetation mosaic, 15 snow and ice, 16 barren or sparsely vegetated, and 17 unclassified)

图2 1981—2020年7—12月美国西部地区降水量（a，单位：mm）、水汽压差（b，单位：kPa）、植被总初级生产力（c，单位：gC·m-2）和火情天气指数（d）的气候态空间分布

Fig.2 The climatological spatial distribution of precipitation (a, Unit: mm), VPD (b, Unit: kPa), GPP (c, Unit: gC·m-2) and FWI (d) in the western United States from July to December during 1981-2020

图3 2025年1月美国洛杉矶山火过程中火点数量及过火面积逐日变化（a）、火点等级分布（b）、洛杉矶及其周边地区FWI的逐日变化（c）及7—9日平均FWI的空间分布（d）

Fig.3 The daily variation of fire spot numbers and burned area (a), the distribution of fire spot grade (b), the daily variation of FWI in Los Angeles and its surrounding areas (c) and the spatial distribution of average FWI from 7 to 9 (d) during the January 2025 Los Angeles wildfires in USA

图4 2024年（a、b、c）及2024年7—12月（d、e、f）美国西部地区降水距平百分率（a、d）（单位：%）、VPD距平（b、e）（单位：kPa）和FWI距平（c、f）的逐月变化（a、b、c）及空间分布（d、e、f） [图4（d）、（e）、（f）中蓝色方框区域（25°N—38°N，120°W—110°W）分别为图4（a）、（b）、（c）的取值区域，数字表示蓝色方框区域平均值]

Fig.4 The monthly variations (a, b, c) and spatial distributions (d, e, f) of precipitation anomaly percentage (a, d) (Unit: %), VPD anomaly (b, e) (Unit: kPa) and FWI anomaly (c, f) in the western United States in 2024 (a, b, c) and from July to December 2024 (d, e, f) (The blue boxed area (25°N-38°N, 120°W-110°W) in Figure 4 (d), (e), and (f) serves as the value-extraction region for Figure 4 (a), (b), and (c), respectively, and the number denotes the average value of the blue boxed area)

图5 1981—2024年7—12月美国西部（25°N—38°N，120°W—110°W；下同）降水、VPD和FWI标准化距平的时间序列（a）和散点图（b）

Fig.5 Time series (a) and scatter plot (b) of standardized anomalies of precipitation, VPD and FWI area-averaged over the western United States (25°N-38°N, 120°W-110°W; the same as below) from July to December during 1981-2024

图6 1980—2020年7—12月美国西部区域平均的降水（a）和VPD（b）观测值和CAS-DASys模拟结果的标准化距平（阴影表示多成员模拟结果的离散度）

Fig.6 Standardized anomalies of observed and CAS-DASys simulated regional average precipitation (a) and VPD (b) in the western United States from July to December during 1980-2020 (The shading represents the spread among multi-members simulation results)

图7 CAS-DAsys大样本模拟的2024年7—12月美国西部降水和VPD标准化距平的散点图

Fig.7 The scatter plot of standardized anomalies of precipitation and VPD in the western United States from July to December 2024 based on the CAS-DAsys large ensemble simulations

图8 基于CAS-DAsys全强迫和自然强迫试验结果拟合的美国西部2024年7—12月降水（a）和VPD（b）标准化距平的概率密度分布

Fig.8 The probability density distribution of standardized anomalies of precipitation (a) and VPD (b) in the western United States from July to December 2024 based on the CAS-DAsys all-forcing and natural-forcing experiment simulations

图9 基于CAS-DAsys全强迫（a）和自然强迫（b）试验结果拟合的美国西部2024年7—12月降水和VPD标准化距平的联合概率密度分布

Fig.9 The joint probability density distribution of standardized anomalies of precipitation （a） and VPD （b） in the western United States from July to December 2024 based on the CAS-DAsys all-forcing （a） and natural-forcing （b） experiment simulations

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2025年1月美国洛杉矶破纪录山火事件的干旱气象条件归因

Attribution of drought-related meteorological conditions for the record-breaking wildfire event in Los Angeles in January 2025

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