Analysis on differences of characteristics and atmospheric circulation causes of meteorological drought during summer in Sichuan-Chongqing region

doi:10.11755/j.issn.1006-7639-2025-03-0355

Abstract

Abstract:

To reveal the spatio-temporal differences and atmospheric circulation causes of summer meteorological drought in the Sichuan-Chongqing region, based on daily observational data and meteorological drought composite index (MCI) of 188 meteorological stations in Sichuan and Chongqing during 1981-2023, the spatio-temporal evolution characteristics of summer drought in Sichuan and Chongqing are analyzed. In addition, monthly reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and climate system monitoring indices are employed to investigate the drought formation mechanisms from the perspectives of circulation patterns, water vapor transport, westerly jet streams, and vertical motion. The results show that droughts in the Sichuan-Chongqing region exhibit strong synchronicity and significant regional differences. Drought in Sichuan mainly concentrates in June and August, while that in Chongqing is more severe from July to August. The drought centers are primarily located in the Sichuan Basin, with a certain degree of synchrony between eastern Sichuan and Chongqing, whereas the drought in the western Sichuan Plateau is relatively weak. During typical drought years, the South Asian High moves northward and strengthens, the Western Pacific Subtropical High is abnormally located further north, water vapor transport at 700 hPa is weakened, and the region is controlled by subsidence motion, resulting in significantly less precipitation. Distinct atmospheric circulation anomalies in different types of drought years are the main cause of the spatial variability of drought in the region.

Key words: meteorological drought, atmospheric circulation, Sichuan and Chongqing region

摘要： 为揭示川渝地区夏季气象干旱的时空差异及其大气环流成因，基于1981—2023年四川和重庆188个气象站观测资料及气象干旱综合指数（Meteorological Drought Composite Index，MCI）分析四川和重庆夏季干旱的时空演变特征，并结合美国国家环境预报中心/国家大气研究中心（National Centers for Environmental Prediction/National Center for Atmospheric Research，NCEP/NCAR）逐月再分析资料及气候系统监测指数资料，从环流形势、水汽输送、西风急流及垂直运动等方面探讨干旱形成机制。结果表明，川渝地区干旱具有同步性强、区域差异显著的特征，四川干旱主要集中在6月和8月，重庆则在7—8月较重；川渝干旱中心主要位于四川盆地，四川东部与重庆表现出一定协同性，川西高原干旱相对较轻。典型干旱年，南亚高压偏强偏北，副热带高压异常偏北，700 hPa水汽输送减弱，区域受下沉运动控制，造成降水显著偏少。不同干旱类型年份的环流异常结构存在显著差异，是干旱空间差异的主要原因。

关键词: 气象干旱, 大气环流, 川渝地区

CLC Number:

P429

HE Huigen, ZHANG Chi, CHENG Qingyan, LI Yonghua, GAN Weiwei, JIN Yan. Analysis on differences of characteristics and atmospheric circulation causes of meteorological drought during summer in Sichuan-Chongqing region[J]. Journal of Arid Meteorology, 2025, 43(3): 355-365.

何慧根, 张驰, 成青燕, 李永华, 甘薇薇, 金燕. 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, 2025, 43(3): 355-365.

Figures/Tables 10

Fig.1 The spatial distribution of weather stations and terrain in Sichuan and Chongqing region

Fig.2 The multi-year monthly average of percentage of stations with drought (a) and drought days (b) in summer in Sichuan and Chongqing during 1981-2023

Fig.3 The spatial distribution of drought days in June (a), July (b), and August (c) in Sichuan and Chongqing (Unit: d)

Fig.4 The number of drought days with different levels in Sichuan (a) and Chongqing (b) from June to August, and two regions in the entire summer (c)

Fig.5 The spatial distribution of average days of light drought (a), moderate drought and above (b), and total drought days (c) during summer in Sichuan and Chongqing (Unit: d)

Fig.6 The percentage of stations with different levels drought in total stations in Sichuan (a) and Chongqing (b) during summer from 1981 to 2023

Fig.7 The composited 500 hPa geopotential height field (black contour lines) and its anomaly field (color shaded) in summer in years with severe drought in Sichuan (a), years with severe drought in Chongqing (b), and years with severe drought both in Sichuan and Chongqing (c) (Unit: gpm) (The area enclosed by the blue line represents Sichuan and Chongqing, the same as below; the pink lines represent the climate average 5 880 gpm line)

Fig.8 The composited 200 hPa geopotential height contours greater than 12 520 gpm (black lines) and the climatological mean of 12 520 gpm (red line) (Unit: gpm), zonal wind speed exceeding 30 m·s-1 (blue thick line) and the climatological mean of zonal wind speed at 30 m·s-1 (pink line) (Unit: m·s-1) at 200 hPa in summer in years with severe drought in Sichuan (a), years with severe drought in Chongqing (b), and years with severe drought both in Sichuan and Chongqing (c)

Fig.9 The composited 700 hPa wind filed (arrow vetcors) and meridional wind anomaly field (color shaded) in summer for years with severe drought in Sichuan (a), years with severe drought in Chongqing (b), and years with severe drought both in Sichuan and Chongqing (c) (Unit: m·s-1)

Fig.10 The composited 700 hPa vertical velocity field in summer in years with severe drought in Sichuan (a), years with severe drought in Chongqing (b), years with severe drought both in Sichuan and Chongqing (c) (Unit: 10-2 Pa·s-1)

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