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.

Under the background of global warming, studying the characteristics of dry-wet climate changes in the Shiyang Rive Basin and their influence on vegetation coverage has significant importance for the ecological environment construction of the basin. Based on the precipitation temperature homogenization index (S) in the Shiyang River Basin from 1971 to 2020, the spatial-temporal changes of the dry-wet climate in the basin were analyzed from the aspects of drought station frequency ratio, drought frequency, and more. Combined with the Normalized Differential Vegetation Index (NDVI) remote sensing data, the influence of dry-wet change on NDVI was analyzed. The results showed that the inter-annual and seasonal S indices showed an increasing trend in the Shiyang River Basin over the past 50 years, with the most pronounced increase in summer. The drought degree and drought occurrence area have shown a decreasing trend in the basin. The intensity of drought in the midstream and downstream were more severe compared to the upstream, with higher drought frequencies in the downstream. The annual NDVI increased with the alleviation of drought, the increase of precipitation and decrease of temperature. The precipitation in the early and middle period of growth, as well as the temperature in the middle period had a great influence on the annual NDVI. In February, May and July, the NDVI had a lag effect in response to drought.

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 the record data of water disasters and the 5-min precipitation of 40 meteorological observation stations along the Shuozhou-Huanghua Railway from 2017 to 2019, the characteristics of railway water disasters and precipitation distribution were analyzed, then the three precipitation factors including continuous precipitation, the hourly maximum precipitation and the 24-hour precipitation were counted, the rainfall warning thresholds of no warning, patrol warning, speed limit warning and blockade warning of railway sections in plains and mountainous areas were formulated by using the mean-standard deviation method and the maximum value method. The results show that the water disasters of the Shuozhou-Huanghua Railway mainly occurred in July and August, and the duration of precipitation was mostly within 48 hours. The precipitation types causing water disasters were mainly local rainstorm, short-time heavy precipitation and long-duration precipitation, the railway water disasters in plain sections were mainly caused by local rainstorm, but the main cause of mountainous sections was long-duration precipitation. For railway section in the plain, the accuracy rate of patrol warning was 88.5%, the false rate was 11.5%, the accuracy rate of speed limit warning was 100%, for the railway section in the mountainous, the accuracy of patrols warning was 88.9% and the false rate was 11.1%. The rainfall warning threshold for railway sections in plains and mountainous areas could provide reference for safe running and efficient operation of railway.

Based on the daily precipitation data at 18 meteorological stations of Hainan Island from 1969 to 2018, the spatio-temporal change characteristics of precipitation randomness were analyzed by using information entropy method, Mann-Kendall trend test and spatial interpolation technique of inverse distance weight. The results show that the uneveness of monthly apportionment of annual precipitation and precipitation days increased from east to west of Hainan Island. In recent 50 years, the monthly apportionment unevenness of annual precipitation and precipitation days showed an increasing trend in northern and western areas and part areas of southern Hainan Island, while it showed a decreasing trend in the rest areas on the whole. The spatial distribution of randomness of daily precipitation was significantly different in the whole year and four seasons in Hainan Island, and they were significantly and positively correlated with the proportion of rainstorm and above rainfall days. In terms of time, the randomness of daily precipitation in the whole year and four seasons increased in most cities (counties) of Hainan Island from 1969 to 2018, especially the probability of strong precipitation increased in four seasons. The rainstorms to torrential rains in central, northwestern, eastern and eastern Hainan Island should be paid enough attention in spring, summer, autumn and winter, respectively.

Based on daily conventional observation data at 19 meteorological stations of Hainan Island from 1980 to 2018, the climatic season in Hainan Island was divided according to China’s meteorological industry standard (QX/T152-2012). Then, the comfortable degree of human body was calculated by using sensible temperature of human body based on ‘golden ratio’ method. And on this basis the comprehensive division of human body comfortable degree was done in each season in Hainan Island by using rotated empirical orthogonal function (REOF), further the optimum comfortable zones of climatotherapy rehabilitation were obtained in Hainan Island. The results are as follows: (1) The climate was mild and moist in Hainan Island, and the annual average temperature was 22.9 to 25.3 ℃, the average annual precipitation was 1157 to 2615 mm, the annual average relative humidity was 74% to 86%, and the annual average specific humidity was 14.8 to 16.4 g·kg^-1, which was suitable to rehabilitation. (2) Compared with the conventional climate statistical method, the meteorological industry standard was more in accordance with season division in Hainan Island. According to the climate division, the summer was from mid-March to mid-November in Hainan Island, the autumn and spring were from mid-November to next mid-March, which indicated that there wasn’t winter in Hainan Island, and the optimum period of climatotherapy rehabilitation appeared in spring and autumn. (3) The comfortable region of human body in spring and autumn located in northern Hainan, central Hainan and southern Hainan. Overall, the climate in central Hainan was the most optimal, and the climate in three regions was stable from 1980 to 2018.

In order to study physical response of cloud seeding, the precipitation enhancement experiment of stratiform and embedded convective cloud on 8 July 2003 in Jilin Province was analyzed in this paper. The background area and response area of cloud seeding for artificial precipitation enhancement effect were identified, and the seedability of cloud was studied. The differences of cloud microphysical characteristics between background area and response area was analyzed. The results are as follows: (1) The ice crystal number concentration in response area was significantly higher than that in the background area. In response area ice crystal number concentration with a diameter from 37.5 μm to 187.5 μm increased obviously. (2) The number concentration of small cloud particles with a diameter less than or equal to 18.5 μm in response area was lower than that in the background area, but the number concentration of large cloud particles with a diameter from 18.5 μm to 45.5 μm in response area was higher than that in the background area. (3) After cloud seeding, supercooled water content decreased, the radar echo intensity increased, and strong radar echo zone also increased. The physical response of cloud seeding was obvious in this experiment.

Abstract: Based on the cloud product of CERES (clouds and earth’s radiant energy system) Aqua Edition 4A SSF (single scanner footprint) data and hourly precipitation observation data, the spatial and temporal distribution characteristics of micro- and macro-scopic cloud parameters in Liaoning Province (38.5°N-43.5°N, 118.5°E-126°E) were analyzed. In addition, the correlation between cloud parameters and rainfall intensities was studied and the precipitation identification indexes based on COD (cloud optical depth) and CWP ( cloud water path ) were established. The results show that cloud developed more vigorous in summer, and the average of CF (cloud fraction), COD, CTH (cloud top height) and CWP reached as high as 62.7%, 17.9, 6.5 km and 252.1 g·m-2, respectively, but in winter they were 48.3%, 7.0, 3.4 km and 106.2 g·m-2, respectively. Only ER ( the effective radius ) of cloud particles reached the maximum in winter. Due to the influence of terrain, the generation condition of cloud in the east (east of 122°E ) of Liaoning was better than that in the west (west of 122°E). Except the CTH was higher in the western part of Liaoning Province, all the other cloud parameters were lower than that in the eastern part. The CF, COD, CWP and ER of particles all increased with rainfall intensities, while CTP ( cloud top pressure) and CTT ( cloud top temperature) showed opposite trend, indicating that the stronger the precipitation was, the thicker cloud layer was, the higher water content was and the larger particle size was. COD and CWP were selected as the precipitating cloud identification factors for its higher correlation coefficients with precipitation intensities. Based on the score of TS (threat score) and HSS (Heidke skill score), 35 and 415 g·m-2 for COD and CWP was selected, corresponding to the maximum TS and HSS scores.

Based on the traffic accidents data on expressway of Hebei Province and conventional observation data at 109 national weather stations from October 2015 to October 2018, the temporal variation characteristics of expressway traffic accidents and the relationship with meteorological factors in summer and winter half years were contrastively analyzed, firstly. Then, the meteorological factors which had obvious influence on traffic accidents were selected by principal component analysis method and the binary Logistic regression model was introduced to establish the meteorological early warning models of expressway traffic accidents in Hebei Province in summer and winter half years, respectively. Finally, the accuracy of two models was tested. The results show that the diurnal and monthly change characteristics of traffic accidents were obvious on expressway of Hebei Province. The frequency of traffic accident in summer half year was 1.4 times more than that in winter half year, and the monthly fluctuation in summer half year was weaker than that in winter half year. The diurnal variation of traffic accidents in summer and winter half years presented  ‘M’ pattern distribution. The traffic accidents in the daytime were more than that in the nighttime, the peak value appeared at 10:00 BST and 15:00 BST, and the traffic accidents at each time in summer half year (except from 18:00 BST to 20:00 BST) were higher than that in winter half year. The meteorological early warning model of expressway traffic accidents in Hebei integrated humidity, precipitation, wind speed and air pressure factors, while the temperature factor was also introduced in model in winter half year. The prediction accuracy of early warning model was above 99% to the samples less than or equal to the mode of traffic accidents, while that was lower to the samples above the mode, but the overall accuracy was still above 80%, which indicated that the model had a certain reference significance to expressway traffic early warning.

From the view of climate system complexity, the nonlinear characteristics of drought were discussed in Northwest China from 1962 to 2017. Based on the monthly meteorological observation data at 159 stations of Northwest China, the standardized precipitation evapotranspiration index (SPEI) was calculated, firstly. Then, the temporal and spatial distribution of drought was analyzed by using empirical orthogonal function (EOF). And on this basis the abrupt change of decomposed time coefficient of SPEI was detected by using moving cut data- approximate entropy (MC-ApEn) method. Finally, the complexity of drought was discussed by using approximate entropy (ApEn) method in Northwest China. The results are as follows: (1) The first EOF mode of SPEI was consistently positive in Northwest China from 1962 to 2017, while the second EOF mode was positive in the east and negative in the west of Northwest China. Compared with time coefficient of the second mode, the climate was wetter in the west and drier in the east than that before the abrupt change, and the change point was approximately in 1980. The drought existed 2-3 a period in Northwest China during 1962-2017. (2) The complexity of drought increased after the abrupt change of 1980 in Northwest China as the whole, so the predictability of drought decreased. Moreover, the complexity of drought in autumn and winter was greater than that in spring and summer in Northwest China from 1962 to 2017, and the complexity was the largest in winter and the smallest in summer.

Based on the numerical prediction interpretation techniques and forecast experiences，the short － term objective forecast system
of meteorological elements for Northwest China is established． With the aid of meteorological data of real － time observation，the
verification and assessments of objective forecast from the system － output for air temperature and precipitation in winter of 2006 have
been performed． The results show: ( 1) The forecast accuracy of maximum and minimum temperature is much higher than that of precipitation
with the accurate rates of 70% and 34%，respectively． ( 2) The factors affecting the forecast accuracies of temperature and
precipitation are the static stability of atmosphere and relative humidity． ( 3) If the system established on month scale，the forecast accuracy
of temperature is expected to have a 10% improvement．