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 atransition from sustained to sudden drought, while Inner Mongolia continued to experience drought. (2) During the same period, the 500hPa 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.

The European Space Agency Climate Change Initiative soil moisture (ESA CCI_SM) product can provide soil volumetric water content data with high spatiotemporal coverage and a long time series. It can be used for drought monitoring on a regional scale. Gansu Province was selected as the study site for ESA CCI_SM testing. Soil volumetric water content data at the 0-10 cm depth from automatic station was used to evaluate the ESA CCI_SM product by analyzing the spatiotemporal variation characteristics of soil moisture in a long time series and construction of a soil moisture condition index (SMCI) for use in drought monitoring. The ESA CCI_SM product showed the best correlation (R=0.71) with observed values in the east of Gansu Province, followed by the middle, the south and Min county of Gansu Province. Overall, the 92% correlation coefficients of the sites were significant and passed 0.01 significant level. ESA CCI_SM indicated that it was more arid in the northwestern regions while it was more humid in the southeastern regions. Soil volumetric water content showed significant seasonal variation, which was relatively more humid in antumn, followed by summer, while in winter and spring it was drier. The SMCI constructed using the ESA CCI_SM product effectively exhibited the summer-autumn drought development from July to October 2002 and the spring-summer drought development from April to June 2009. This product had good drought monitoring capability in rain-fed agricultural areas in the middle and the east of Gansu Province.