Under the severe situation of global warming, regional high temperature and drought events are becoming more frequent, posing a major threat to ecological environment, food security, economic development and life and health. From April to June 2024, high-temperature and drought events occurred again in North China, Northwest China, and Southwest China, causing significant losses in agricultural production. This study utilized various data to preliminarily analyze the characteristics and causes of the high-temperature and drought processes in above three regions. The results show that the drought in southwest China mainly occurred in April, while the drought in North China and Northwest China began to emerge in April, with the intensity gradually increasing and the range expanding from May to June. With the intensification of drought, the abnormal range of regional maximum temperature expanded significantly. The number of hot days in Northwest China reached a new record, and the highest temperature anomaly reached its peak in May, which was one month ahead of the most severe drought period (June) in this region. The high temperatures in southwest China and North China were close to historical extremes. Further analysis indicates that the drought in North China is mainly influenced by the circulation in the Pacific region, while high temperatures are mainly affected by the circulation in the low-latitude Pacific and the Western Pacific Warm Pool. The drought in Northwest China is mainly influenced by the Western Pacific Subtropical High and the Arctic Vortex in the Northern Hemisphere, and the main influence on high temperatures comes from the North Atlantic. The factors affecting high temperatures and drought in the Southwest China are more complex, but mainly concentrated in the Northern Hemisphere Subtropical High and the low-latitude Pacific and Indian Oceans. From the perspective of circulation and water vapor, the main causes of the drought in North China and Northwest China are the development and maintenance of the continental high pressure, while the drought process in Southwest China is affected by the northward shift of the Western Pacific Subtropical High, which allows the dry and hot air currents from the Indian subcontinent to control this area, leading to water vapor divergence and ultimately causing high-temperature drought.

In the spring of 2023, a severe meteorological drought occurred in southwestern China, which had a serious impact on the local social economy. In order to deeply understand the causes of this drought event and further provide a basis for the prediction technology of spring drought in southwestern China, causes of the spring drought event were analyzed from the perspective of SST (sea surface temperature) and MJO (Madden-Julian Oscillation) by using station-observed data, NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data, NOAA (National Oceanic and Atmospheric Administration) SST and other data, choosing T-N wave activity flux, composite analysis and other methods. The results showed that: (1) The spring drought over southwestern China in 2023 was a compound dought-heatwave event occurred in the middle in March, developed and expanded westward in April, and maintained in May. (2) In March, the horseshoe-shaped SST anomalies in the North Pacific caused the westerly jet stream to drift southward and westward, suppressing the precipitation in southwestern China. (3) In April, the anticyclonic circulation anomaly near the Bay of Bengal induced by warm SST in the Indian Ocean through Kelvin wave and the cyclonic circulation anomaly from the South China Sea to the Philippines triggered by warm SST in the Northwest Pacific through Rossby wave resulted in northerly winds in the south of southwestern China, which caused the divergence of water vapor and the development of drought in southwestern China. (4) MJO, which maintained in the western Pacific for a long time in May, stimulated the cyclonic anomaly from the South China Sea to the Philippines in lower troposphere due to Gill response, reduced the transport of southerly water vapor, and maintained drought in southwestern China.

From January to June 2023, meteorological droughts of varying degrees occurred in southwestern China, eastern North China, northern East China, central southern China, southern South China, and central Northeast China, seriously affecting agricultural production and restricting local economic development. To improve the ability to respond to drought disasters, timely carry out disaster prevention and reduction work, and conduct real-time summaries of drought situations. This article uses K index, MCI index, T-N flux and CABLE land surface model, as well as meteorological observation data, reanalysis data, soil moisture data to comprehensively analyze the spatiotemporal distribution characteristics and causes of regional drought events. The results are as follows: (1) In the first half of 2023, severe regional drought occurred in southwestern China and eastern Inner Mongolia. The southwestern region experienced a transition from sustained to sudden drought, while Inner Mongolia continued to experience drought. (2) During the same period, the 500 hPa geopotential height field showed a two trough and two ridge pattern at mid to high latitudes. The western Pacific subtropical high pressure abnormally extended westward and uplifted northward, and the Rossby waves at mid latitudes in Eurasia were abnormally weak, resulting in a weakening of the influence of flat westerly winds and cold air in mid to high latitudes, resulting in less precipitation in the southwest and eastern Inner Mongolia, leading to regional drought. (3) In the first half of 2023, the winter La Niña event shifted to the spring El Niño event, resulting in weak convective activity in the southwest region and triggering sustained hot and dry weather; The distribution of sea surface temperature sensitive areas in Inner Mongolia has led to the stability of its upstream high-pressure ridge, resulting in drought and limited rainfall in the eastern region of Inner Mongolia.

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.