The impact of mid-latitude atmospheric circulation anomalies on wildfires caused by California drought in summer 2024

doi:10.11755/j.issn.1006-7639-2025-05-0655

Journal of Arid Meteorology ›› 2025, Vol. 43 ›› Issue (5): 655-666.DOI: 10.11755/j.issn.1006-7639-2025-05-0655

• Column on “California Wildfires and Drought” • Previous Articles Next Articles

The impact of mid-latitude atmospheric circulation anomalies on wildfires caused by California drought in summer 2024

YANG Yaoxian¹^,²(), YAO Yubi¹(), YANG Rengui¹, GAO Yubin¹, ZHANG Weiwei¹^,⁶, DENG Mengyu³^,⁴, XIAO Miaoyuan⁵

1. Lanzhou Resources & Environment Voc-Tech University， Lanzhou 730021， China
2. Nagqu Plateau Climate and Environment Observation and Research Station of Tibet Autonomous Region， Northwest Institute of Eco-Environment and Resources， Chinese Academy of Sciences， Nagqu 852000， Xizang， China
3. Sichuan Provincial Meteorological Observatory， Chengdu 610072， China
4. Heavy Rain and Drought-Flood Disasters in Plateau and Basin Key Laboratory of Sichuan Province， Chengdu 610072， China
5. Engineering Design & Research Institute of Sichuan University Co. Ltd.， Chengdu 610065， China
6. Tiedong District Meteorological Bureau of Siping City， Jilin Province， Siping 136000， Jilin， China

Received:2025-08-13 Revised:2025-09-08 Online:2025-10-31 Published:2025-11-09

中纬度大气环流异常对2024年加州干旱引发山火的影响

杨耀先¹^,²(), 姚玉璧¹(), 阳仁贵¹, 高瑜昺¹, 张伟伟¹^,⁶, 邓梦雨³^,⁴, 肖淼元⁵

1.兰州资源环境职业技术大学，甘肃兰州 730021
2.那曲高寒气候环境西藏自治区野外科学观测研究站，西藏那曲 852000
3.四川省气象台，四川成都 610072
4.高原与盆地暴雨旱涝灾害四川省重点实验室，四川成都 610072
5.四川大学工程设计研究院有限公司，四川成都 610065
6.吉林省四平市铁东区气象局，吉林四平 136000

通讯作者: 姚玉璧
作者简介:杨耀先（1988—），男，甘肃武威人，博士，讲师，主要从事气候动力学与陆面过程研究。E-mail： yangyaox@lzre.edu.cn。
基金资助:
兰州资源环境职业技术大学2025年度黄河流域生态方向预研项目“气候变化对农业生态的影响研究”(2025LZHLSY-05);兰州资源环境职业技术大学科技创新协同工作资助经费及兰州资源环境职业技术大学重大科技项目“地质灾害监测预警产教融合研究”(X2022ZD-04)

Abstract

Abstract:

Summer wildfires in the Northern Hemisphere occur more and more frequently under global warming, posing a serious threat to the ecological environment. This study utilized ERA5 daily atmospheric reanalysis data spanning from 1980 to 2024 and daily fire weather index data from the European Forest Fire Information System, and analyzed the causes of wildfire events in California in summer 2024 from the perspective of anomalous circulation in mid-high latitudes both on transient and intraseasonal timescales through the physical decomposition principle of transient asymmetric anomaly and diagnosis of wave activity. The results are as follows: 1) In early July 2024, the energy of quasi-steady Rossby waves over the North Pacific propagated eastward, which strengthened and maintained the anomalous anticyclone off the west coast of the North American continent. The temperature increase caused by adiabatic downward motion favored the occurrence and spread of wildfires. 2) The transient asymmetric anomalous flows indicate that the anomalous anticyclone over California has strengthened the subtropical high and increased the risk of wildfires. 3) The decomposition results of transient asymmetric anomaly show that the transient asymmetric anomalous flows can indicate the meteorological conditions and risk of wildfires more clearly. Therefore, the prediction of transient asymmetric flows should play a key role in the forecast and early warning for extreme weather events.

Key words: California, wildfire, drought, anomalous circulation, synoptic-scale transient asymmetric anomaly

摘要：

随着全球气候变暖，北半球夏季山林火灾事件频发，严重威胁生态环境。本文利用1980—2024年欧洲中期天气预报中心（European Center for Medium-Range Weather Forecasts，ECMWF）的ERA5逐日大气再分析资料与欧洲森林火灾信息系统（European Forest Fire Information System）的2024年夏季逐日火灾天气指数资料，基于天气尺度瞬变扰动的物理分解原理和大气长波活动诊断分析方法，对季节内和天气瞬变扰动两个时间尺度上的环流异常特点及影响2024年夏季美国加利福尼亚州（简称“加州”）山林火灾的机制进行了分析研究。结果表明：1）2024年7月上旬，北太平洋上空的准定常Rossby波能量向东传播，有助于北美大陆西岸异常高压反气旋的加强与维持，并通过绝热下沉增温，有利于山林火灾的爆发与蔓延。2）天气尺度瞬变扰动流场促使加州上空异常高压反气旋增强，进一步加强副热带高压，并提升山林火灾发生的风险。3）天气尺度瞬变扰动分解的结果表明，瞬变天气扰动场由于包含了天气尺度瞬变扰动过程中的纬向非对称性特征，其对区域性山林火灾发生的气象条件与风险指示意义明确，因此，天气尺度瞬变扰动场的分析可在山林火灾事件的预报预警中发挥作用。

关键词: 加利福尼亚州, 山林火灾, 干旱, 环流异常, 天气尺度瞬变扰动

CLC Number:

P448

YANG Yaoxian, YAO Yubi, YANG Rengui, GAO Yubin, ZHANG Weiwei, DENG Mengyu, XIAO Miaoyuan. The impact of mid-latitude atmospheric circulation anomalies on wildfires caused by California drought in summer 2024[J]. Journal of Arid Meteorology, 2025, 43(5): 655-666.

杨耀先, 姚玉璧, 阳仁贵, 高瑜昺, 张伟伟, 邓梦雨, 肖淼元. 中纬度大气环流异常对2024年加州干旱引发山火的影响[J]. 干旱气象, 2025, 43(5): 655-666.

Figures/Tables 11

Fig.1 Spatial distribution of the mean fire weather index in the western United State in summer of 2024 （the area surrounded by red wire frame is the research area）

Fig.2 The time-latitude （a） and time-longitude （b） sections of fire weather index in California， USA， in summer of 2024

Fig.3 Spatial distribution of the mean fire weather index in the western United State on 15 June （a）， from 1 to 11 July （b） and on 24 July （c） in 2024

Fig.4 Time series of area mean fire weather index， surface air temperature （SAT） and VPD anomalies in California in summer of 2024

Fig.5 Spatial distribution of standardized precipitation index in the western United States in summer of 2024 （a） and inter-annual variations of the regional mean standardized precipitation index in California in summer from 1980 to 2024 （b）

Fig.6 The daily time-longitude sections of transient asymmetric anomalous meridional wind at 200 hPa along 45.75°N in June （a） and July （b） of 2024 （Unit： m·s-1）， daily variation of atmospheric long-wave index in summer 2024 （c）， and inter-annual variation of atmospheric long-wave index from July 1 to 11 during 1980-2024 （d）

Fig.7 The averaged geopotential height perturbation field （the color shaded， Unit： gpm） and T-N wave activity fluxes （vectors， Unit： m2·s-2） at 200 hPa （a）， geopotential height （the color shaded， Unit： gpm） and horizontal winds （vectors， Unit： m·s-1） perturbation field at 500 hPa （b）， 500 hPa anomalous vertical velocity （the color shaded， Unit： 0.01 Pa·s-1）（c） and anomalous surface air temperature （green contour lines， Unit： K） and anomalous vapor pressure deficit field （the color shaded， Unit： hPa）（d） from 1 to 11 July 2024 （Yellow solid line and purple solid line represent 5 860 gpm feature line of geopotential height from1 to 11 July 2024 and climatology mean result， respectively）

Fig.8 The synoptic-scale transient asymmetric anomalous fields （a， d， g）， original fields （b， e， h）， and the sum of climatology mean and anomalous zonal mean fields （c， f， i） of geopotential height field （the color shaded， Unit： gpm） and horizontal winds field （vectors， Unit： m·s-1） at 500 hPa from 14 to 16 June 2024

Fig.9 The synoptic-scale transient asymmetric anomalous fields （a， d， g）， original fields （b， e， h）， and the sum of climatology mean and anomalous zonal mean fields （c， f， i） of geopotential height field （the color shaded， Unit： gpm） and horizontal winds field （vectors， Unit： m·s-1） at 500 hPa from 23 to 25 June 2024

Fig.10 The anomalous vertical velocity at 500 hPa （the color shaded， Unit： 0.01 Pa·s-1）（a， b）， anomalous surface air temperature （the green contour lines， Unit： K） and anomalous vapor pressure deficit （the color shaded， Unit： hPa）（c， d） on 15 June （a， c） and 24 July （b， d） 2024

Fig.11 Diagram of the impact of anomalous atmospheric circulation in mid-latitude on wildfire in California

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The impact of mid-latitude atmospheric circulation anomalies on wildfires caused by California drought in summer 2024

中纬度大气环流异常对2024年加州干旱引发山火的影响

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