2022年长江流域农业干旱发展过程及气象成因

Development Process and Meteorological Causes ofAgricultural Drought in the Yangtze River Basin in 2022

2022年长江流域发生了大面积的干旱,此次干旱涉及范围广,持续时间长,对于农业、生态等方面都造成了较大影响。降水量相比同期减少,气温增加,导致土壤含水量降低,农业干旱同步发生。复演长江流域此次农业干旱的发展过程,探寻其气象成因,对于完善干旱发生机理的认识,实现干旱的有效应对具有重要意义。研究基于ERA5数据,对比2022年土壤含水量与多年同期均值,从时空维度揭示了2022年农业干旱的主要土壤含水量特征;采用标准化土壤湿度指数值,通过与往期干旱事件对比,阐明此次农业干旱的严重性;最后,从大气环流角度与外强迫场海温角度,分析了此次干旱的气象成因。分析表明,2022年,6-9月全流域的农业干旱程度分别为:无旱、极旱、极旱、极旱。流域遭受长达3个月的农业极端干旱,其中依据数值判断,8月干旱程度最深。就干旱气象成因而言,西太副高2022年6-9月较往年同期影响面积增大、强度增强,且西太副高位置异常偏西,近乎包括流域整个范围,导致流域整体处于单纯西太副高控制之下;同时,长江流域夏季降水与前一年秋冬季大西洋北部、太平洋北部的海温,以及同年春夏季太平洋东部、大西洋及印度洋海温关系较为密切,高相关性时段内的海温与往期均值存在差异性,引起相关干旱。

In 2022,a large drought occurred in the Yangtze River Basin,which was widespread and long-lasting and had a major impact on agriculture,ecology and other aspects.Precipitation decreased compared to the same period,and the temperature increased,leading to a de⁃crease in soil water content and the synchronization of agricultural drought occurrence.Reviewing the development process of this agricultural drought in the Yangtze River Basin and exploring its meteorological causes are of great significance in improving the understanding of the drought occurrence mechanism and realizing an effective response to the drought.In this study,based on ERA5 data,the main soil water content characteristics of the 2022 agricultural drought are revealed from the spatial and temporal dimensions by comparing the soil water content in 2022 with the average values of the same period in many years;the severity of this agricultural drought is clarified by comparing it with the previous drought events using the standardized soil moisture index values;and,finally,the meteorological causes of this drought are analyzed from the perspectives of atmospheric circulation and sea-surface temperatures (SSTs) of the external forcing field. The analysisshowed that in 2022, the agricultural drought degree in the whole basin from June to September was: no drought, extreme drought, extremedrought, and extreme drought, respectively. The basin suffered three months of extreme agricultural drought, of which August had the deep⁃est drought based on numerical judgment. In terms of the meteorological causes of drought, the influence area and intensity of the WesternPacific Subtropical High( WPSH) increased from June to September 2022 compared with the same period in previous years, and the positionof the WPSH was abnormally westward, almost including the entire range of the basin, resulting in the basin as a whole being under the con⁃trol of the WPSH alone;at the same time, the summer precipitation in the Yangtze River basin was closely related to the SSTs in the northernpart of the Atlantic Ocean and the northern part of the Pacific Ocean in the previous fall/winter, as well as to the SSTs in the eastern part ofthe Pacific Ocean , Atlantic and Indian Ocean in the same year′s spring/summer, and there is a discrepancy between the SSTs during thehigh correlation period and the mean values of the previous periods, causing the related droughts.