Abstract: Hail days observation data from 95 weather stations in Hunan province and NECP 0.5°×0.5° reanalysis data from 1979 to 2018 was used to analyze the climatic characteristics and influencing factors of hail days in Hunan by linear trend estimation, M-K test, wavelet analysis, and similarity analysis. The results showed that the season of hail in Hunan province was obvious, the months from January to May are the main hail months, and the number of hail days in March was the most, which was a typical spring hail area; In general, hail in Hunan province was more in the northwest and less in the southeast, decreasing from northwest to southeast; In recent 40 years, the number of hail days in Hunan province had decreased significantly, and the decrease trend was the most significant in March, at the same time, the number of hail days presents periodic changes, especially in cycles 2~3 years and 4~6 years, 3 years cycle fluctuation had been the main trend since 2000; The decrease of hail days in Hunan province mainly came from the significant decrease of hail days in the areas with high incidence of hail, most stations in northwestern Hunan, northern Hunan, southern Hunan and central Hunan had a significant decrease of hail days; The spatial distribution and variation trend of hail in Hunan province were significantly correlated with the distribution and variation trend of atmospheric stability K index, in the regions with monthly average K index lower than 23, the high value area of hail corresponds to the relatively high value area of K index at the same latitude, and the regions with significantly decreased number of hail days correspond to the regions with significantly increased K index.

Key words: hail, spatial and temporal variation, K index, atmospheric stability