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.

The climate in the Yellow River Basin has undergone significant changes in recent years, which has a significant impact on surface hydrological and ecological processes in the basin. Studying the spatial and temporal variation of evapotranspiration in the Yellow River Basin is indicative for understanding deeply land-atmosphere interactions and regional water resources management. In this paper, the appliability of ERA5-Land evapotranspiration in the Yellow River Basin was evaluated using in-situ observations of Haibei, SACOL (Semi-Arid Climate and Environment Observatory) and Yucheng stations which are selected as representative stations from the source region, Hetao region and the lower reach of the Yellow River Basin, respectively. Then based on monthly latent heat flux from ERA5-Land data, the spatial and temporal variation of evapotranspiration in the Yellow River Basin in the past 42 years (1980-2021) are analyzed using EOF (Emipirical Orthogonal Function), power spectrum and regression analysis methods. The results show that ERA5-Land data can reflect the variation characteristics of evapotranspiration at Haibei, SACOL and Yucheng stations with good correlation and small error and root mean square deviation, which is applicable for the analysis on spatial and temporal variation of evapotranspiration in the Yellow River Basin. There are multi-timescale variations of evapotranspiration in different regions of the Yellow River Basin, with significant oscillation periods of main 5 a and 15 a, and obvious inter-annual and inter-decadal variations. The first mode in different regions of the Yellow River Basin characterizes the consistency in spatial distribution, which decreases around 2004. The second mode is dipole distribution, indicating the reverse change in space. The deceleration of evapotranspiration in the Yellow River Basin in the past 42 years is not same in different regions, with the fastest rate of -3.74 mm·a^-1 in the lower reaches and -2.82 mm·a^-1 in the Hetao area, while the deceleration in the source area is relatively gentle. The summer evapotranspiration variability is the largest, and the deceleration is faster in the Hetao area and the lower reaches. The winter evapotranspiration variability is smaller, but the source area has the largest winter evapotranspiration deceleration of -0.48 mm·a^-1.

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.

Based on monthly average reanalysis data from NCEP/NCAR from 1948 to 2016, the horizontal and vertical structure of the South Asia high (SAH) and their long-term variation characteristics were investigated. The results show that the horizontal structure of the SAH on 70 hPa, 100 hPa, 150 hPa and 200 hPa in different typical anomaly years appeared double centers mode and zonal and meridional enlargement, compared with the climatology state, but the horizontal width change of the SAH on different levels was different. The maximum wind speed of easterly jet constrained by internal air of the SAH weakened from 1948 to 2016 as a whole, while that of westerly jet had no significant change tendency. The dynamic and thermal vertical structures of the SAH including easterly jet, westerly jet, and air temperature anomaly were different during 1948-2016. The thickness of the SAH had obvious annual change, and it varied from 6.32 km to 6.42 km in the past 69 years. The geopotential height values of the SAH center on different levels rose about 0.1 gpkm during 1975-1980, and the east-west oscillation and south-north displacement of the central location were obvious, but the change ranges were different on different levels.

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.