Characteristics of high temperature and drought during summer in Chongqing and its response to La Niña event

doi:10.11755/j.issn.1006-7639(2023)-06-0873

Abstract

Abstract:

The La Niña event was so related to China's climate that it had a significant impact on the high temperature and drought in Chongqing. In recent years, the high temperature and drought in Chongqing had repeatedly reached new highs. Studying the characteristics of high temperature and drought in the region and its response to the La Niña event can improve the prediction and early warning capabilities of high temperature and drought in Chongqing. Based on the MCI (meteorological drought composite index), high temperature days, NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis of circulation field data and Hadley SST (sea surface temperature) data from 1981 to 2022, the temporal and spatial distribution characteristics of meteorological drought stations and high temperature days during summer in Chongqing were analyzed. Furthermore, the impact of La Niña event on summer drought stations and high temperature days in Chongqing and its circulation anomaly characteristics were explored. The results showed that summer was the season with the highest frequency and longest duration of drought in Chongqing. Drought and high temperatures were mainly distributed in the northeast and along the Yangtze River. High temperature and meteorological drought promoted so each other that prolonged high temperature was conducive to the development of severe drought, while prolonged drought was also conducive to the occurrence of extreme maximum temperatures. In the early winter and spring, the SST in the equatorial middle east Pacific was in La Niña state, which was conducive to the occurrence of high temperature and drought in Chongqing during summer. The weak La Niña event was conducive to the occurrence of summer high temperatures in Chongqing, while the moderate intensity La Niña event was conducive to the development of drought. Both the central and eastern types of La Niña event were conducive to the occurrence of summer high temperatures and drought in Chongqing. The reason was that, influenced by the La Niña event, the south Asian high pressure was larger, stronger, and northward. Affected by this, the western Pacific subtropical high was larger, stronger, and northward. Furthermore, high-altitude jets located in the northern region of China. These factors were important circulation reasons for high temperature and drought in Chongqing during summer. The middle and lower layers of the troposphere in Chongqing region were controlled by weak southwest winds. Combined with the two ridges and one trough pattern of the Eurasian mid high latitude circulation, forming a climate environment that was not conducive to the southward movement of cold air. As a result, Sichuan Basin, including Chongqing had been controlled by sinking airflow for a long time, which was the main reason for frequent high temperatures and droughts in Chongqing.

Key words: Chongqing, high temperature and drought, La Niña event, cause of circulation, downdraft

摘要：

拉尼娜事件与我国气候密切相关，近年来重庆地区频繁出现的高温干旱与拉尼娜事件的关联值得深入研究。研究重庆高温干旱的特征及其对拉尼娜事件的响应，以期对该地区的高温干旱预测和预警提供科学依据。基于1981—2022年气象干旱综合指数MCI（Meteorological Drought Composite Index）、高温日数、NCEP/NCAR（National Centers for Environmental Prediction/National Center for Atmospheric Research）再分析环流场和Hadley海温数据，分析重庆夏季高温和气象干旱的时空分布特征，探寻拉尼娜事件对高温干旱的影响及其环流异常特征。结果表明：夏季是重庆干旱发生频率最高且持续时间最长的季节，高温干旱主要集中在东北部及长江沿线地区。高温与干旱之间存在相互促进的关系，持续高温促进重度干旱的形成，而长期干旱也可能导致极端高温的发生。赤道中东太平洋海温在冬、春季处于拉尼娜状态，对重庆夏季的高温和干旱有显著影响。弱拉尼娜事件倾向于引发高温，而中等强度拉尼娜事件更易导致干旱。中部型和东部型拉尼娜事件均对重庆夏季高温和干旱产生显著影响。拉尼娜事件影响下的南亚高压偏大、偏强、偏北，西太平洋副热带高压随之产生的偏大、偏强、偏北，以及高空急流位置偏北，是导致重庆夏季高温和干旱发展的重要环流因素。夏季重庆地区对流层中下层主要受偏弱的西南风控制，结合欧亚中高纬环流呈“两脊一槽”格局，形成不利于冷空气南下的气候环境，从而导致包括重庆地区在内的四川盆地长期受下沉气流控制，是重庆地区高温和干旱频发的主要原因。

关键词: 重庆, 高温干旱, 拉尼娜, 环流成因, 下沉气流

CLC Number:

P429

HE Huigen, ZHANG Chi, WU Yao, LI Yonghua, YANG Qin, MU Yujiao. Characteristics of high temperature and drought during summer in Chongqing and its response to La Niña event[J]. Journal of Arid Meteorology, 2023, 41(6): 873-883.

何慧根, 张驰, 吴遥, 李永华, 杨琴, 穆玉娇. 重庆夏季高温干旱特征及其对拉尼娜事件的响应[J]. 干旱气象, 2023, 41(6): 873-883.

Figures/Tables 11

Fig.1 The seasonal variation of drought frequency and drought days (a), monthly variation of drought frequency, drought days and high temperature days of Chongqing during summer from1981 to 2022

Fig.2 The inter-annual variation of high temperature days with maximum temperature above 35 ℃， the stations above the middle drought and the total stations of drought in Chongqing during summer from 1981 to 2022

Fig.3 The spatial distribution of average days of light drought (a), moderate drought and above (b), total drought (c) during summer from 1981 to 2022 (Unit: d)

Fig.4 The spatial distribution of high temperature days with maximum temperature above 35 ℃ (a), 37 ℃ (b) and 40 ℃ (c) of Chongqing in summer from 1981 to 2022 (Unit: d)

Tab.1 The correlation coefficient between high temperature days with different thresholds and drought stations with different levels of Chongqing in summer from 1981 to 2022

干旱等级	不同高温阈值
干旱等级	35 ℃以上	37 ℃以上	40 ℃以上
轻旱	0.37^*	0.31^*	0.13
中旱	0.53^**	0.49^**	0.34^*
重旱	0.65^**	0.65^**	0.57^**
特旱	0.58^**	0.63^**	0.67^**
干旱	0.61^**	0.60^**	0.49^**

Fig.5 The composited SST anomaly filed in previous winter (a) and spring (b) of 2001, 2006, 2011 and 2022 (Unit: ℃)

Fig.6 The correlation coefficient between the average days of high temperature (a, c), drought stations (b, d) of Chongqing with SST in previous winter (a, b) and spring (c, d) in summer from 1981 to 2022 (The scoring areas have passed the significant test at the 95% confidence level)

Tab.2 The statistics of La Niña events from 1982 to 2022

序号	起止年月	强度	类型	序号	起止年月	强度	类型
1	1984年10月至1985年6月	弱	东部	7	2010年6月至2011年5月	中等	东部
2	1988年5月至1989年5月	强	东部	8	2011年8月至2012年3月	弱	中部
3	1995年9月至1996年3月	弱	东部	9	2017年10月至2018年3月	弱	东部
4	1998年7月至2000年6月	中等	东部	10	2020年8月至2021年3月	中等	东部
5	2000年10月至2001年2月	弱	中部	11	2021年9月至2023年1月	弱	东部
6	2007年8月至2008年5月	中等	东部

Tab. 3 The days of high temperature and drought stations in different intensities and types of La Niña year in summer from 1981 to 2022

不同强度和类型的拉尼娜事件	高温日数/d	干旱总站次/站次	中旱以上站次/站次
强	16.7	887	285.0
中等	23.5	1 436	918.3
弱	30.5	1 134	666.7
中部型	26.6	1 560	978.5
东部型	25.4	1 145	666.7
多年平均	24.0	959	527.7

Fig.7 The composited 500 hPa geopotential height filed (black contour lines) and its anomaly filed (color shaded) (a, Unit: gpm), 700 hPa wind filed (arrows) and meridional wind anomaly filed (color shaded) (b, Unit: m·s-1) in summer of 2001, 2011 and 2022 (The pink lines represent the climate average 5 880gpm line)

Fig.8 The composited Walker circulation anomaly field averaged over 5°S—5°N (a, shaded area show anomalous vertical velocity, the vertical velocity has been magnified by 100 times, Unit: 10-2 Pa·s-1; vector wind show the synthesis of anomalous vertical velocity and anomalous u wind, Unit: 10-2 Pa·s-1), 200 hPa height filed and zonal wind anomaly (b, contour lines show mean field, Unit: gpm; shaded area show zonal wind anomaly, Unit: m·s-1) and 700 hPa vertical velocity filed (c, Unit: 10-2Pa·s-1) in summer of 2001, 2011 and 2022 （pink dotted line represent the climate average 12 520 gpm line）

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