USING OBSERVED HAIL TO QUALITY EXTREME HAIL CLIMATE IN VIET NAM. PART I: DATA QUALITY CONTROL AND CLIMATOLOGICAL CHARACTERISTICS OF HAIL

In this study, we focus on studying data and calculating climatic features of hail. In this study, a hail dataset was created by combining historic records from 186 meteorological stations for the period 1961 - 2021. The data are obtained from several sources including observations from the Viet Nam Meteorological and Hydrological Administration (VNMHA), annual reports of the Viet Nam Institute of Meteorology, Hydrology and Climate change (IMHEN) and the Viet Nam Disaster Management Authority (VDMA). The data used in this study is defined from the official data sources. Therefore, the data quality control shows that this data may be considered good available data of hail. Research results for 1961 - 2021 show that the highest number of hail events was observed in the Northwest (743 events), and in the Northeast (557 events) subregions; the lowest number of hail events was observed in the South Central (16 events) and the South (27 events) subregions. The higher frequency duration of hail occurs from March to May, with the peak in April. The largest hail diameter, recorded in Vietnam is 12 cm at Bac Ha station on March 27, 2013; the common largest hail diameter size in history at stations is around 3 - 5 cm at the Northern stations and 1 - 3 cm at the southern stations.