Abstract: Temporal and spatial distributions of hail disaster were analyzed using hail and meteorological disaster data from nine stations in Weifang from 1952 to 2012.The results show that the hail disaster is serious in Weifang during this period of time.The frequency of occurrence for large hails is higher,and in most cases,the hail disaster lasts for more than 20 minutes.The hail occurrence exhibits strong local characteristics,and topography plays a crucial role in determining the spatial distribution of hail days,with a high value in the mountain and a low one in the plain.Most hail storms occur in June.The maxima appears in the middle ten-day of June.The monthly variation of hail days in Weifang shows a ruled pattern,which increases first and then decreases later.Normally hail occurs at 14-16 p.m.There is a significant inter-decadal variation in the number of hail days,existing about 16 and 2 years of periodic variations.The climatic abrupt change in the number of hail days appears in 1970.After 1970,especially after 1974,the hail occurrence frequency is found to increase.The number of hail days shows a pronounced negative correlation with the corresponding cold-air activity index.

Key words: Hail, Inter-annual variation, Periodic variation, Climate abrupt change