Analysis of circulation characteristics and influencing mechanisms of atypical below-normal precipitation type during main flood season over the Yangtze River Basin

doi:10.11755/j.issn.1006-7639-2026-04-0625

Abstract

Abstract:

To further investigate precursor signals and circulation mechanisms for the main flood season with atypical below-normal precipitation over the Yangtze River Basin, this study identifies 2023 as an analog year with similar external climate forcing to 2025, which was characterized by below-normal rainfall during the June-August main flood season, based on analyses of pre-flood-season climate factors from 1990 to 2025. Using multi-source observational and reanalysis datasets, a comparative analysis of precipitation, hydrological conditions, and atmospheric circulation characteristics is performed for 2023 and 2025. The results show that both main flood seasons exhibited below-normal total precipitation, weaker Meiyu rainbands, and reduced river inflows. Compared with 2023, a shorter Meiyu duration and much less precipitation occurred in 2025. During the main flood seasons of the two years, the western Pacific subtropical high (WPSH) persisted in a westward position, which was generally unfavorable for large-scale water vapor transport toward the Yangtze River Basin. Differences in dominant mechanisms between the two years are concluded as follows: The shortened Meiyu in 2025 resulted from both the northward-positioned south Asian high (SAH) and the pronounced northward jump of WPSH during June-July. The precipitation deficits in 2025 in the middle and lower reaches of the Yangtze River Basin were attributed to the weakened moisture transport which resulted from the weakened synergistic effects of SAH and the westerly jet during July-August, and southward landfall of typhoons over South China. In contrast, the WPSH ridge line in 2023 was near its climatological mean position. Characterized by larger meridional oscillations but weaker northward displacement of the SAH and a stronger westerly jet stream, 2023 featured markedly stronger upper-level divergence and pumping-effect over the Yangtze River Basin than 2025.

Key words: Yangtze River Basin, main flood season, atypical below-normal precipitation type, analogous year, atmospheric circulation

摘要：

为深入分析长江流域主汛期非典型少雨情况下的前兆信号和环流影响机制，本文基于1990—2025年汛前气候因子分析，筛选出与2025年（主汛期6—8月少雨年）气候外强迫相似的2023年，利用多源观测与再分析资料，对比分析2025年和2023年雨情、水情及大气环流特征。结果表明：两年主汛期均呈现降水总量偏少、梅雨偏弱、来水偏少特征，且2025年梅雨期更短、降水偏少更多。两年主汛期西太平洋副热带高压（简称副高）持续偏西，总体不利于水汽向长江流域大规模输送。二者差异在于：2025年南亚高压位置整体更偏北，6—7月副高显著北跳，导致梅雨期缩短；7—8月南亚高压与西风急流的协同作用减弱，台风主要登陆华南，削弱向长江流域的水汽输送，导致中下游降水偏少。2023年副高脊线位置接近气候平均态，南亚高压南北摆动幅度大但偏北程度较弱，西风急流更强，高空辐散抽吸作用明显强于2025年。

关键词: 长江流域, 主汛期, 非典型少雨型, 相似年, 大气环流

CLC Number:

P426.6

WANG Haiyan, WANG Xiaoci, ZHANG Ling, Zhou Yunyi, MENG Yingjie. Analysis of circulation characteristics and influencing mechanisms of atypical below-normal precipitation type during main flood season over the Yangtze River Basin[J]. Journal of Arid Meteorology, 2026, 44(4): 625-635.

王海燕, 王孝慈, 张灵, 周耘逸, 孟英杰. 长江流域非典型少雨型主汛期环流特征及其影响机制分析[J]. 干旱气象, 2026, 44(4): 625-635.

Figures/Tables 13

Fig.1 Distribution of meteorological and hydrological stations in the Yangtze River Basin

Fig. 2 Mean sea level pressure (black contours) and its anomalies (color shaded) (a, Unit: hPa), anomaly fields of composite zonal wind-vertical velocity (vectors, Unit: m·s-1) and vertical velocity (the color shaded, Unit: 10-2 Pa·s-1) (b) in spring 2025

Fig.3 Monthly PDO index from January 1990 to July 2025， and evolution of Ni?o3.4， IOBW， and TNA sea temperature anomalies from August of the weak La Ni?a event year to July of the subsequent year

Tab.1 Anomalies of snow cover area over the Qinghai-Xizang Plateau in previous winter and concurrent spring for weak La Ni?a event ending years during 1990-2025

弱拉尼娜事件结束年	积雪面积距平
弱拉尼娜事件结束年	前冬	当年春季
1996	-0.11	-0.22*
2001	-0.37*	-0.08
2006	-0.21*	-0.07
2009	-0.34*	-0.06
2018	-0.20*	0.16
2021	-0.27*	-0.17*
2023	-0.14	-0.03
2025	-0.05	0.17

Tab.2 Precipitation anomalies over the Yangtze River Basin and its upper， middle-lower reaches during June-August of 2025 and 2023

流域	2025年				2023年
流域	6—8月	6月	7月	8月	6—8月	6月	7月	8月
全流域	-7.1	11.1	-23.9	-10.2	-3.9	-10.0	-0.6	0
上游	-0.8	5.3	-11.5	5.5	-4.5	-25.1	4.3	5.7
中下游	-11.0	13.8	-32.0	-22.5	-3.3	-2.5	-3.7	-4.1

Fig.4 Spatial distribution of precipitation anomaly over the Yangtze River Basin from June to August in 2025 （a） and 2023 （b）（Unit： %）

Fig.5 Latitude-time sections of daily precipitation averaged along 90°E-122°E over the Yangtze River Basin from June to August in 2025 （a） and 2023（b）（Unit： mm）（The red box indicates the latitudinal range of the Yangtze River Basin）

Fig.6 Daily variations of inflow for the Three Gorges Reservoir （a）， discharge and water levels at Hankou Station （b） and Datong Station （c） from June to August in 2025 and 2023

Fig.7 Monthly mean 500 hPa geopotential height （black contours） and its anomalies field （the color shaded） from June to August in 2025 and 2023 （Unit： dagpm）（The region bounded by the red solid line represents the Yangtze River Basin）

Fig.8 Daily evolution of the ridge line （a） and the westward extension point （b） of the western Pacific subtropical high from June to August in 2025 and 2023

Fig.9 Latitude-time sections of the 200 hPa south Asian high ridge line （black line）， zonal wind （green lines， Unit： m·s-1）， climatological mean ridge line of the south Asian high （blue line）， and horizontal divergence averaged along 90°E-122°E （the color shaded， Unit： 10-6 s-1） from June to August in 2025 （a） and 2023 （b）（The red box indicates the latitudinal range of the Yangtze River Basin， the same as below）

Fig.10 Latitude-time sections of 700 hPa wind field （vectors， Unit： m·s-1）， and vertically integrated moisture flux divergence from the surface to 700 hPa （the color shaded， Unit： 10-5 kg·m-2·s-1） averaged along 90°E-111°E （a， c） and 111°E-122°E （b， d） in 2025 （a， b） and 2023 （c， d）

Tab.3 Information of typhoons making landfall in China and affecting the Yangtze River Basin in 2025 and 2023

生成年份	名称	生成时间	登陆地点
2025年	蝴蝶	6月11日08：00	海南省东方市
	丹娜丝	7月5日02：00	台湾省嘉义县
	韦帕	7月18日凌晨	广东省台山市
	竹节草	7月23日20：00	上海市奉贤区
	杨柳	8月8日11：00	台湾省台东县
2023年	泰利	7月14日11：00	广东省湛江市
2023年	杜苏芮	7月21日08：00	福建晋江沿海

References 34

[1]	陈蔚, 管兆勇, 杨华栋, 等, 2025. 2022年夏季西太平洋副热带高压异常强盛且稳定维持与长江中下游持续性极端高温事件[J]. 气象学报, 83(1): 33-45.
[2]	陈文, 丁硕毅, 冯娟, 等, 2018. 不同类型ENSO对东亚季风的影响和机理研究进展[J]. 大气科学, 42(3): 640-655.
[3]	储鹏, 姚素香, 2020. 夏季东亚副热带西风急流的季节内变化及其与我国东部降水的关系[J]. 气象科学, 40(4): 458-466.
[4]	何慧根, 张驰, 成青燕, 等, 2025. 川渝地区夏季气象干旱差异及大气环流成因分析[J]. 干旱气象, 43(3): 355-365. DOI
[5]	华文剑, 冯慧婷, 崔亚朱, 等, 2025. 2022年夏季长江流域极端高温的研究进展与展望[J]. 地球科学进展, 40(5): 456-472. DOI
[6]	李双吟, 张耀存, 黄丹青, 等, 2024. 盛夏亚洲大陆上空急流变化的两类模态及其与东亚大气环流异常的联系[J]. 高原气象, 43(4): 895-904. DOI
[7]	李延, 陈斌, 徐祥德, 2023. 青藏高原冬春积雪异常对中国东部夏季降水频次和强度变化的影响[J]. 大气科学, 47(4): 1 231-1 246.
[8]	李忆平, 张金玉, 岳平, 等, 2022. 2022年夏季长江流域重大干旱特征及其成因研究[J]. 干旱气象, 40(5): 733-747. DOI
[9]	李永华, 徐海明, 刘德, 2009. 2006年夏季西南地区东部特大干旱及其大气环流异常[J]. 气象学报, 67(1): 122-132.
[10]	彭京备, 刘舸, 孙淑清, 2016. 2013年我国南方持续性高温天气及副热带高压异常维持的成因分析[J]. 大气科学, 40(5): 897-906.
[11]	史芳斌, 张方伟, 万汉生, 2002. 2001年长江流域干旱及成因分析[J]. 水利水电快报, 23(8): 28-29.
[12]	孙昭萱, 张强, 周长艳, 等, 2026. 2022年长江流域极端高温干旱的环流异常特征及其影响机制[J]. 气象学报, 84(3): 486-499.
[13]	王文, 许金萍, 蔡晓军, 等, 2017. 2013年夏季长江中下游地区高温干旱的大气环流特征及成因分析[J]. 高原气象, 36(6): 1 595-1 607.
[14]	夏智宏, 陈笑笑, 2025. 1961-2022年长江流域复合极端气候事件演变特征[J]. 长江科学院院报, 42(11): 1-8. DOI
[15]	全国气候与气候变化标准化技术委员会, 2022. 区域性暴雨过程评估方法:GB/T 42075-2022[S]. 北京: 中国标准出版社.
[16]	张存杰, 张思齐, 宁惠芳, 2024. 近60 a中国极端天气气候事件变化趋势及2023年特征分析[J]. 干旱气象, 42(4): 536-552. DOI
[17]	张强, 2022. 科学解读“2022年长江流域重大干旱”[J]. 干旱气象, 40(4): 545-548. DOI
[18]	张庆云, 宣守丽, 孙淑清, 2018. 夏季东亚高空副热带西风急流季节内异常的环流特征及前兆信号[J]. 大气科学, 42(4): 935-950.
[19]	张人禾, 张若楠, 左志燕, 2016. 中国冬季积雪特征及欧亚大陆积雪对中国气候影响[J]. 应用气象学报, 27(5): 513-526.
[20]	张雯, 董啸, 薛峰, 2020. 不同PDO位相下El Niño发展年和La Niña年东亚夏季风的季节内变化[J]. 大气科学, 44(2): 390-406.
[21]	张雯, 薛峰, 张潇潇, 等, 2023. 2022年夏季中国高温环流特征及其与热带海面温度异常的关系[J]. 气候与环境研究, 28(5): 559-572.
[22]	张宇, 李耀辉, 魏林波, 等, 2013. 南亚高压与西太平洋副热带高压对我国西南地区夏季降水异常的影响[J]. 干旱气象, 31(3): 464-470.
[23]	张云帆, 翟丽妮, 林沛榕, 等, 2021. 长江中下游典型流域旱涝与旱涝/涝旱急转演变规律及其驱动因子研究[J]. 武汉大学学报:工学版, 54(10): 887-897.
[24]	周波涛, 钱进, 2021. IPCC AR6报告解读: 极端天气气候事件变化[J]. 气候变化研究进展, 17(6): 713-718.
[25]	周军, 任宏昌, 王蒙, 等, 2023. 2022年夏季长江流域干旱特征及成因分析[J]. 人民长江, 54(2): 29-35.
[26]	朱玉祥, 丁一汇, 刘海文, 2009. 青藏高原冬季积雪影响我国夏季降水的模拟研究[J]. 大气科学, 33(5): 903-915.
[27]	祝传栋, 任荣彩, 2023. 夏季南亚高压两类东-西振荡过程的联系及其天气效应对比[J]. 大气科学, 47(1): 53-69.
[28]	KAO H Y, YU J Y, 2009. Contrasting eastern-Pacific and central-Pacific types of ENSO[J]. Journal of Climate, 22(3): 615-632. DOI URL
[29]	LI X Y, LU R Y, CHEN G X, et al, 2024. Western North Pacific tropical cyclones suppress Maritime Continent rainfall[J]. npj Climate and Atmospheric Science, 7: 251. DOI:10.1038/s41612-024-00810-2.
[30]	MANTUA N J, HARE S R, ZHANG Y, et al, 1997. A Pacific interdecadal climate oscillation with impacts on salmon production[J]. Bulletin of the American Meteorological Society, 78(6): 1 069-1 079. DOI URL
[31]	QIN P C, XU H M, LIU M, et al, 2020. Assessing concurrent effects of climate change on hydropower supply, electricity demand, and greenhouse gas emissions in the Upper Yangtze River Basin of China[J]. Applied Energy, 279: 115694. DOI:10.1016/j.apenergy.2020.115694.
[32]	YAO T D, XUE Y K, CHEN D L, et al, 2019. Recent third pole’s rapid warming accompanies cryospheric melt and water cycle intensification and interactions between monsoon and environment: Multidisciplinary approach with observations, modeling, and analysis[J]. Bulletin of the American Meteorological Society, 100(3): 423-444. DOI URL
[33]	YIN Z C, SONG X L, ZHOU B T, et al, 2024. Traditional Meiyu-Baiu has been suspended by global warming[J]. National Science Review, 11(7): nwae166. DOI:10.1093/nsr/nwae166.
[34]	ZSCHEISCHLER J, WESTRA S, VAN DEN HURK B J J M, et al, 2018. Future climate risk from compound events[J]. Nature Climate Change, 8(6): 469-477. DOI