Drought disaster is one of the most frequent meteorological disasters in the Gannan Plateau, which seriously affects agricultural and animal husbandry production and ecological environment security in this region. Monthly precipitation and air temperature data from 31 meteorological stations in the Gannan Plateau and its surrounding areas from 1973 to 2022 are used to characterize meteorological drought employing the Standardized Precipitation Evapotranspiration Index (SPEI), and the temporal and spatial distribution of drought and its variations on annual and seasonal scales in the Gannan Plateau are analyzed by using Mann-Kendall test and Sen’s slope estimation methods. Results show that the annual SPEI in the Gannan Plateau presented significant downward trend with an obvious turning point in 1986, and the whole Gannan Plateau tended to be dry in the past 50 years. There were seasonal differences in the variation trend of drought, and the trend of drought intensified in summer and autumn, but in spring and winter it mitigated. In addition, there were spatial differences in the trend of annual and seasonal SPEI. In summer, it presented drought intensification trend in the middle and eastern regions of the Gannan Plateau, and in spring it showed similar to that in summer, but the area and degree of drought intensification were obviously smaller than that in summer. While in winter, it showed drought decreasing trend in the whole region. There were obvious spatial differences in the frequency of drought with different levels in the Gannan Plateau at the annual and seasonal scales. Light drought occurred frequently in the central and eastern parts of the Gannan Plateau, while medium and severe drought occurred frequently in the southern part of the Gannan Plateau, and the frequency of serious drought was less across the whole regions. Overall, the frequency of drought in the western was less than that in the central and eastern parts of the Gannan Plateau.

Based on 31 aviation records of low-level wind shear, surface observational data at Shijiazhuang Zhengding international airport of Hebei Province and NCEP/NCAR reanalysis data from 2014 to 2017, the characteristics of low-level wind shear and corresponding weather situations were analyzed. The results show that the low-level wind shear mainly occurred in the afternoon and nightfall, with the peak at 14:00 BST. The majority of low-level wind shear events occurred in spring, and the low-level wind shear events occurred most in April. The number of low-level wind shear events at Zhengding international airport was the highest in 2015. The mainly weather situations which were conducive to occurrence of low-level wind shear events were northwest airflow type, vortex type, west wind trough type and horizontal trough type. Furthermore, low-level wind shear occurred most under the weather situation of northwest airflow type, especially in spring and winter. The convective weather under the vortex weather situation was prone to occurrence of low-level wind shear. In addition, more attention should be paid on 3 hours and 1 hour anallobaric and negative temperature variation under the northwest airflow weather situation, as well as allobaric and variable temperature in a short time under the vortex weather situation for forecasting low-level wind shear.

Based on the NCEP reanalysis data, conventional observation data and microwave radiometer data, the background field, characteristics of the boundary layer and formation cause and maintenance mechanism of a sustained heavy fog process during 11-15 January 2019 in central and southern Hebei Province were analyzed. The results show that the fog generated under the background of stable zonal circulation, during which weak short-wave troughs moved eastward quickly, and two dry short-wave troughs promoted the formation of heavy fog and the strengthening of the fog, respectively. The fog was mainly radiation fog and only a few tens of meters in  height. The two-layer structure of temperature inversion layer, weak water vapor convergence and southwest water vapor transport  on the ground inversion layer provided water vapor source for heavy fog, the cooling of weak cold air caused by northerly wind and cooling of radiation at night were thermodynamic conditions for the development of the fog. The positive vorticity in the lower layer and the divergence and sinking in the middle troposphere were dynamic factors promoting maintainess  and development of the fog, the combination of long-wave radiation in the clear night sky and turbulent mixing promoted cooling and humidification in the boundary layer. During the later period of the heavy fog, the temperature inversion layer changed from two-layer structure to a single-layer structure. The dissipation of the fog was caused by the intrusion of strong cold air and destruction of stationary structure.

Based on the hourly minimum visibility, precipitation and relative humidity of 61 national meteorological stations during the period 2016-2017, the characteristics of low visibility along eight main highways in Hebei Province were investigated. The results show that low visibility appeared most in autumn and winter while least in spring. In autumn and winter, the 02:00-03:00, 03:00-07:00, 05:00 were the peak hours for the appearance of  low visibility of 200-500 m, 50-200 m and 0-50 m, respectively. The frequency of  low visibility along Daqing-Guangzhou highway (Beijing-Hengshui section and Hengshui-Daming section), Shijiazhuang-Anyang highway and Qingdao-Yinchuan highway was higher, while it was lower along Beijing-Qinhuangdao highway and Coastal highway. The low visibility of 200-500 m usually appeared from 20:00 to 07:00. The frequency of low visibility of 200-500 m along Hengshui-Daming section, Shijiazhuang-Anyang highway and Qingdao-Yinchuan highway was higher after 00:00, while it was opposite for Beijing-Qinhuangdao highway. The visibility of 50-200 m along Beijing-Hengshui section and Qingdao-Yinchuan highway occured mainly during 04:00-07:00, and it occured maily during 05:00-08:00 along Beijing-Shanghai highway and Shijiazhuang-Huanghua highway. The peak time of frequency of the visibility of 50-200 m occured during 03:00-07:00 along Shijiazhuang-Anyang highway. The frequency of the visibility of 0-50 m along various highways decreased significantly.The peak value of low visibility of 0-50 m occured mainly at 00:00 and 05:00 along Beijing-Hengshui section(Raoyang-Anping section), while it occurred during 03:00-07:00 along Hengshui-Daming section. The low visibility of 0-50 m was easier  to  occure along Botou section of Shijiazhuang-Huanghua highway than other sections  of  that.

Based on the meteorological observation data at traffic weather stations along the highways of Hebei Province and the highway traffic accidents and closed-control data caused by the meteorological conditions during 2012-2017, the influence factors of the intensity of high impact weather, durations, risk zoning levels, single traffic flow, topography and occurrence period, etc. on the highway traffic passing were selected, firstly. Then the risk level forecast models of fog, road icing and heavy rainfall disasters were established by using the multifactor weighted method. And on this basis, the integrated risk level forecast model of highway traffic based on three weather conditions was built, and the grade standards were defined with the discrimination index of highway closed-control time caused by fog, road icing and heavy rainfall. Through testing, the accuracy rate of the forecast products of highway traffic integrated risk level model based on the meteorological conditions was 76.7%, which can meet the demand of daily traffic meteorological service.

The NDV I of Ejina Oasis was calculated based on the data derived from Landsat TM /ETM + images in 1996, 2000, 2002 and 2006, and in light ofNDV I’s value the land coverwas divided into four types: the bare land, the sparse vegetation area, the lower vegetation area and the dense vegetation area. Through the comparison of the different grade vegetation area change before and afterwater devision, the restoring effect of the vegetation in Ejina Oasis can be found out, and this can supp ly the scientific foundation for the Heihe water - division p lan of the next step. The monitoring results show that the ecological environment of Ejina Oasis kep t deteriorating before 2002, but after seven - yearwater division from upper andmiddle reaches of Heihe River, the environment deterioratingwas alleviated and vegetation was restoring stage by stage.