Characteristics and cause analysis of extreme and persistent drought in summer, autumn and winter in 2022/2023 in Hunan Province

doi:10.11755/j.issn.1006-7639(2023)-06-0910

Abstract

Abstract:

Hunan is a region prone to drought disasters. Conducting an analysis of the characteristics and causes of drought events is of great practical significance for improving the monitoring and prediction level of drought disasters in Hunan and reducing disaster losses. Based on daily precipitation data from ground observation stations and reanalysis data, the characteristics and causes of persistent extreme drought events that occurred in Hunan in the summer, autumn and winter of 2022/2023 are analyzed. The results indicate that the continuous drought in the summer, autumn and winter of 2022/2023 in Hunan has the characteristics of significantly less precipitation (The average accumulated precipitation in the whole province was the least in the same period since 1961) and a long duration (201 days). And in the summer of 2022, there was also a rare extremely high temperature heatwave throughout the entire Yangtze River basin, with multiple indicators such as average temperature and high temperature days in Hunan reaching historical extremes since 1961, which had a serious impact on industrial and agricultural production and people’s lives in Hunan. The ongoing drought event in summer, autumn and winter is closely related to sea surface temperature and circulation anomalies. In the early spring, the La Niña event and the negative phase mode of the Indian Ocean dipole led to the enhancement of the Walker circulation, and the west Pacific subtropical high (referred to as the “WPSH”) strengthened and extended westward and uplifted northward. From August to November 2022, the WPSH extended westward to 105°E, and the Hunan region was controlled by it, the prevailing downdraft led to the development of drought in summer and autumn in Hunan. From December 2022 to early February 2023, the WPSH was weaker compared to the same period in previous years, and the East Asian trough was strengthened and its location was east of Hunan, making it difficult to guide cold air southward to affect Hunan. The Indian-Myanmar trough was weaker, which was not conducive to the development of southwest airflow in front of the trough. The water vapor transport over Hunan region was hindered, leading to sustained drought in winter in Hunan.

Key words: persistent drought in summer, autumn and winter, Hunan, drought causes, atmospheric circulation

摘要：

湖南是干旱灾害多发区，针对湖南地区开展干旱事件特征与成因分析，对于提高湖南干旱灾害的监测预测水平、减少灾害损失具有重要现实意义。基于地面观测站日降水数据和再分析资料，分析2022/2023年夏秋冬季湖南发生的持续极端干旱事件特征和成因。结果表明，这次湖南夏、秋、冬三季连旱具有降水显著偏少（全省平均累积降水量为1961年以来历史同期最少）、持续时间长（历时201 d）的特点，同时2022年夏季还伴随罕见的长江全流域性极端高温热浪，湖南平均气温、高温天数等多项指标均达到1961年以来历史同期极值，给湖南工农业生产和人民生活带来严重影响。本次夏秋冬持续干旱事件与海温和环流异常密切相关，前期春季拉尼娜事件和印度洋偶极子负位相模态导致沃克环流增强，西太平洋副热带高压（简称“西太副高”）加强西伸和北抬。2022年8—11月西太副高西伸至105°E，湖南地区受其控制，盛行下沉气流，导致湖南夏秋干旱发展；12月至2023年2月上旬，西太副高相比历年同期偏弱，东亚大槽增强，且位置在湖南以东，难以引导冷空气南下影响湖南，印缅槽偏弱，不利于槽前西南气流发展，湖南地区水汽输送受阻，导致冬季湖南干旱持续。

关键词: 夏秋冬三季连旱, 湖南, 干旱成因, 大气环流

CLC Number:

P466

XIE Ao, LUO Boliang, DENG Jianbo, GAO Xiaxia. Characteristics and cause analysis of extreme and persistent drought in summer, autumn and winter in 2022/2023 in Hunan Province[J]. Journal of Arid Meteorology, 2023, 41(6): 910-922.

谢傲, 罗伯良, 邓剑波, 高霞霞. 湖南2022/2023年夏秋冬季持续极端干旱事件特征及成因分析[J]. 干旱气象, 2023, 41(6): 910-922.

Figures/Tables 14

Tab.1 Classification of meteorological drought grade based on SPI

干旱等级	干旱类型	SPI
1	无旱	-0.5<SPI
2	轻旱	-1.0<SPI≤-0.5
3	中旱	-1.5<SPI≤-1.0
4	重旱	-2.0<SPI≤-1.5
5	特旱	SPI≤-2.0

Fig.1 Time series of average precipitation from summer to winter （a） and in summer （b）， autumn （c） and winter（d）in Hunan during 1961-2022/2023

Fig.2 Distribution of precipitation anomaly percentage in summer （a）， autumn of 2022 （b） and in winter from 2022 to 2023 （c）（Unit： %）

Fig.3 Evolution of station numbers with light， moderate， severe and extreme drought in Hunan from June 1， 2022 to February 28， 2023

Fig.4 Variation of station numbers with daily maximum temperature of 35 ℃ and 40 ℃ above in Hunan from June 1 to August 31，2022

Fig.5 Time series of average air temperature （a） and regional high temperature days （b） from June to August during 1961-2022，and spatial distributions of temperature anomaly （c， Unit： ℃） and regional high temperature days anomaly （d， Unit： d） in Hunan from June to August 2022

Tab.2 Monthly characteristic index anomalies of western Pacific subtropical high from June 2022 to February 2023

月份	面积指数	强度指数	脊线指数/°N	北界指数/°N	西伸脊点/°E
2022年6月	2.0	59.0	0.3	0.2	-3.8
2022年7月	7.3	190.5	0.1	0.1	-19.1
2022年8月	10.7	333.9	0.2	2.2	-42.9
2022年9月	4.8	73.5	5.0	3.6	-38.1
2022年10月	4.7	107.7	1.2	0.7	-34.0
2022年11月	5.0	94.3	0.6	0.7	-29.0
2022年12月	-0.3	-15.8	-1.4	-2.9	17.3
2023年1月	-0.8	-22.9	2.0	-0.1	16.4
2023年2月	-0.2	-5.1	3.0	-0.3	15.1

Fig.6 The 500 hPa geopotential height （black contours） and anomaly （color shaded， Unit： gpm）（a）， the anomaly of 850 hPa horizontal wind （arrow vectors， Unit： m·s-1） and vertical wind speed （color shaded， Unit： 10-2 Pa·s-1）（b）， and vertically integrated water vapor flux （vectors， Unit： kg·m-1·s-1） and water vapor flux divergence anomaly （color shaded， Unit： 10-7 kg·m-2·s-1）（c） from June to July 2022 （The red contours are climate state， the dotted area indicates that the anomaly exceeded the extreme value since 1981. the same as below）

Fig.7 The 500 hPa geopotential height （black contours） and anomaly （color shaded， Unit： gpm）（a）， the anomaly of 850 hPa wind field （arrow vectors， Unit： m·s-1） and vertical wind speed （color shaded， Unit： 10-2 Pa·s-1 ）（b）， and vertically integrated water vapor flux （vectors， Unit： kg·m-1·s-1） and water vapor flux divergence anomaly （color shaded， Unit： 10-7 kg·m-2·s-1）（c） from August to November 2022

Fig.8 The 500 hPa geopotential height （black contours） and anomaly （color shaded， Unit： gpm）（a）， the anomaly of 850 hPa wind field （arrow vectors， Unit： m·s-1） and vertical velocity （color shaded， Unit： 10-2 Pa·s-1 ）（b）， and vertically integrated water vapor flux （vectors， Unit： kg·m-1·s-1） and water vapor flux divergence anomaly （color shaded， Unit： 10-7 kg·m-2·s-1）（c） from December 2022 to the first ten-day period of February 2023

Fig.9 Correlation coefficient between the total precipitation in summer，autumn and winter in Hunan and SST in the Northern Hemisphere in early spring from 1981 to 2021/2022 （contours， only displaying contour lines that pass the significance test at α=0.10） and SSTA in spring of 2022 （color shaded， Unit： ℃）（a）， and temporal evolution of Niño3.4 index from January 2021 to July 2022 （b）

Fig.10 The distribution of correlation coefficient between the total precipitation in summer， autumn and winter in Hunan and the OLR at the same period from 1981 to 2021/2022 （contours， only displaying contour lines that pass significance test at α=0.10） and anomaly of the OLR from August 2022 to February 2023 （color shaded， Unit： W·m-2）

Fig.11 The longitude-height profiles of ω （Unit： Pa·s-1） and the wind field anomaly composition of u and ω （arrow vectors， Unit： m·s-1） over the equatorial region （a， c， e） and the area between 24.5°N and 30.5°N （b， d， f） from June to July 2022 （a， b）， from August to November 2022 （c， d） and from December 2022 to the first ten-day period of February 2023 （e， f）

Fig.12 The schematic diagram of the impact of SST and atmospheric circulation anomaly on persistent drought event in summer antumn and winter in 2022/2023 in Hunan （The color shaded on the bottom map shows the SSTA from March to May in 2022， and the upper contours are 500 hPa potential height field from August to November 2022）

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