In order to deeply understand the causes of the abnormal drought and high temperature climate event in the Yangtze River Basin in summer 2022 and improve the climate prediction technology, this paper makes a comprehensive analysis from the perspective of atmospheric circulation anomaly by using temperature and precipitation data from more than 2400 observation stations and NCEP/NCAR reanalysis circulation data from 1951 to 2022, and using T-N wave activity flux, apparent heat source Q1 (Q2) diagnosis and composite analysis, anomaly analysis and other methods. The main conclusions are as follows: (1) In summer of 2022, the disturbance originating from the North Atlantic region was unusually strong at 500 hPa, triggering an obvious large trough and ridge activity when it was propagating eastward along the mid-and high-latitude westerly belt. The wave energy mainly propagated eastward along the westerly belt, without the characteristic of propagating southeastward in East Asia, resulting in the northward location of cold air activity, which hardly affected the Yangtze River Basin. (2) In summer of 2022, the 500 hPa height field showed a significant positive anomaly disturbance over the Qinghai-Tibet Plateau region, which further strengthened in August and moved eastward to the Yangtze River Basin, inducing the westward extension of the Northwest Pacific subtropical high, making the subtropical high appear as an east-west zonal distribution. The western part of the subtropical high completely controlled the Yangtze River Basin area. On the one hand, the subtropical high blocked the cold air from the north to the south, on the other hand, the subtropical high maintained the sinking movement for a long time, which was not conducive to precipitation and conducive to sinking and warming. (3) In summer 2022, the location of the tropical convection area (apparent heat source) was abnormally south to the south of the equator (the climate state is between 5°N and 20°N), which has two impacts: one is to cause the ascending branch of the Hadley meridional circulation (Hadley Cell) to be anomalously southward, and the Yangtze River Basin was an anomalous sinking area in August, which is not conducive to precipitation and conducive to the appearance of the sinking warming effect. The other is to cause the weak Asian tropical summer monsoon and strong East Asian subtropical summer monsoon in summer 2022, and the low-frequency signal propagation to the middle and lower reaches of the Yangtze River was obviously weak, which are unfavorable to precipitation process in the middle and lower reaches of the Yangtze River. (4) The synergistic effect of three circulation anomalies in the high latitudes, mid-low latitudes, and the tropics caused an anomalous drought and high temperature climate event in the Yangtze River Basin in summer of 2022. To predict the summer precipitation or high temperature and drought in the Yangtze River Basin, it is necessary to pay attention to the occurrence and future propagation characteristics of the disturbance signal at 500 hPa in the North Atlantic region, the occurrence and movement characteristics of the 500 hPa height field disturbance over the Qinghai-Tibet Plateau, the changes in the location of the tropical convective region (heat source) and the accompanying changes in the intensity of the tropical summer monsoon, and the propagation characteristics of low-frequency signal in advance.
Drought is one of the natural disasters with the widest global impact. The anomalous drought and heatwave event that occurred in the Yangtze River Basin in summer of 2022 is not only of high intensity but also of long duration, it is a rare and significant drought event leading to very serious socioeconomic impacts in China. In view of the extreme nature of this event, this paper reveals the possible influence of atmospheric circulation and external forcing anomalies on this drought event based on an objective analysis of the evolutionary characteristics of this event. It is found that the meteorological drought index and soil moisture monitoring results consistently indicate that this drought event started to appear in June, developed rapidly in July, and further expanded and intensified in both extent and intensity in August. At the same time, the overall temperature in the basin was high, with the number of high temperature days exceeding 40 days in some areas. In addition, anomaly of evapotranspiration over the basin in summer was the second highest on record since 1960, second only to the high temperature drought event in 2013, which further exacerbated the degree of water deficit in the Yangtze River Basin. From the perspective of circulation characteristics, the abnormal intensifying and westward extension of the western Pacific subtropical high pressure, the small area and weak strength of the polar vortex and the intensifying and eastward shift of the South Asian high pressure in summer jointly led to weak water vapor transport conditions and prevailing sinking air currents in the Yangtze River Basin, making the overall conditions unfavorable for the occurrence of precipitation. The persistence of the La Niña event, the appearance of negative Indian Ocean Dipole (IOD) and the persistence of the negative snow cover anomaly in the northwestern Tibet Plateau in spring may be the main external forcing factors leading to the circulation anomaly in this summer.
In the summer of 2022, there was a climate anomaly with the highest average temperature and less precipitation since 1961 in China, accompanied by the strongest nationwide high temperature processes (except northeastern China) and a wide range and strong summer drought in the middle and lower reaches of the Yangtze River and Sichuan and Chongqing. For the persistence and extremity of the high temperature and drought event in this summer in China, this paper analyzes the temporal and spatial distribution characteristics and cirulation situation based on the daily maximum temperature and precipitation of 2162 meteorological stations in China from June to August 2022 and the daily reanalysis data of NCEP (National Centers for Environmental Prediction) /NCAR (National Center for Atmospheric Research), which will be of some references for the forecast of summer high temperature and drought with different time scales in southern China. The results show that in the summer of 2022, a total of 48 198 high temperature events occurred in 76.0% of the stations in China, among which 36.6% of the stations experienced 3001 extreme high temperature events. The stations with more than 20 extreme high temperature events all distributed in the Sichuan Basin, and the high temperature situation was more severe this year than the typical high temperature years since the 21st century. The nationwide high temperature process lasted from June 13 to August 30, a total of 79 days, and the strongest high temperature period was from August 11 to 24. According to the comprehensive ranking of high temperature station numbers, duration, intensity and impact range from strong to weak, the order is East China, Central China, southwestern China, northwestern China, North China and South China, among which, the extreme was the most in southwestern China, while there was no high temperature in northeastern China. The spatial and temporal distribution of drought is basically similar to that of high temperature, and the strongest drought period in China was in mid-August. In the summer of 2022, the 500 hPa over the middle and high latitudes of Eurasia showed a “two ridges and one trough” pattern, especially in July and August, the high pressures ridge near the Ural Mountains and the Sea of Okhotsk formed periodic blocking high. The strong subtropical system blocked the active cold air between the two high pressures to the north of 50°N most of the time, resulting in the pattern of “flood in the north and drought in the south” in China. The Iran high at low latitude extended abnormally to the east, and the western Pacific subtropical high was slightly northward and abnormally extended to the west. The air flow in the control area of the high pressure zone formed by the long-term connection of the two high pressures diverged and sank, which continuously blocked the transport of water vapor to the middle latitude, and was not conducive to the precipitation in the Yangtze River basin. At the same time, the south Asia high at high-level was abnormally eastward and moved to the opposite direction of western Pacific subtropical high at mid-level, which superimposed over the range of 80°E-120°E in the middle and late August, resulting in a stable barotropic structure of the high pressure system controlling a wide range of China, and the center was located over Sichuan and Chongqing region, which made Sichuan-Chongqing region become the large value center of high temperature days and the extreme high temperature event times.
Based on the daily meteorological observation data at 441 national meteorological stations in southwestern China in summer from 1961 to 2022, the basic climatic situation, characteristics of high temperature and drought disasters and their main impacts in southwestern China in summer 2022 are analyzed. The results show that the severity of this extreme high temperature and drought event is historically rare. Compared with the historical corresponding period, the average temperature and the extreme maximum temperature were the highest, the precipitation was the least, and the high-temperature days was the most in the summer of 2022 in southwestern China. In addition, the persistent high temperature was accompanied by a severe meteorological drought in eastern part of southwestern China. The 105 meteorological stations of the central Xizang, most areas of Sichuan, most areas of Chongqing, the north of Guizhou and local regions of central Yunnan happened extreme droughts. Under the impacts of the compound high temperature and drought, the output of some crops in the east of southwest China reduced, even extremely, the inflow of rivers appeared a rare phenomenon of ‘returning to dry in flood season’, and the power load hit a new record and the hydropower generation decreased sharply, resulting in a shortage of energy supply. Moreover, several forest fires broke out in eastern Sichuan Basin and western Chongqing. This article aims to understand this extreme high temperature and drought event from a scientific perspective, facilitate the development of meteorological disaster risk assessment, provide scientific and technological support for improving disaster prevention and mitigation and dealing with climate change.
Based on the data of daily precipitation and mean temperature from 80 national meteorological stations in Anhui Province from 1961 to 2022, the processes of regional extreme climate events are identified according to the objective identification technique for regional extreme events. Average intensity, duration and average influence range are further extracted, which are applied to establish comprehensive intensity assessment model, and then regional high temperature and drought processes in 2022 are comprehensively evaluated. The results show that the average temperature in Anhui Province in the summer of 2022 is 2.2 ℃ higher than normal, which is the highest in the same period since 1961.The precipitation in 2022 is 40% less than normal, which is the fourth lowest since 1961. Persistent high temperature and little rainfall led to continuous severe drought in summer and fall in the south of the Huaihe River in Anhui Province. There are six regional high temperature processes in the summer of 2022, and the high temperature process from August 1 to 23, 2022 has reached the "super strong" level, which rank the fourth in history and is inferior to the high temperature processes in 1966, 1967 and 2013. However, the annual cumulative comprehensive intensity of high temperature in 2022 reached 4496, which is the highest since 1961.Two regional drought processes occurred in the summer and autumn of 2022. Compared with the nine strongest regional drought processes in summer and autumn since 1961, by the end of September 30, 2022 the regional drought process since July 28 has lasted 65 days, and the intensity level is "super strong", which is inferior to the processes in 1966, 1967, 1978 and 2019.
The frequent occurrence of extreme climate events caused by global climate change has become a common challenge for scientific community and human society. Due to diverse driving factors and complex spatio-temporal processes, there are significant differences in various regions of the world. Based on the daily precipitation, temperature and other observation data of 76 national meteorological stations in Hubei from 1961 to 2022, the regional hot and drought events in Hubei since 1961 are identified according to the regional hot process monitoring index and the regional drought process monitoring evaluation method. On this basis, the change characteristics of frequency, duration, intensity and influence of the events are analyzed. The results show that regional hot events increase in frequency and intensity, and occur year after year. The change trend of regional drought event frequency is not significant, but it presents a characteristic of mass, continuous and repeated occurrence. Compound hot and drought events increase significantly and their intervals are shortened. The comprehensive intensity of the hot process in the summer of 2022 is the strongest since 1961, which superimposes with the drought in the Yangtze River Basin, producing a chain complex impact from meteorological drought to hydrological drought, agricultural drought and socio-economic drought. Under the background of global warming, the frequent occurrence of extreme hot, drought, compound hot and drought events might become a new normal of climate in Hubei. It is urgent to strengthen the research on the causes of extreme events and disaster risk assessment, and improve the ability to cope with extreme hot, drought and their compound disasters.
