Abstract:Based on a comprehensive collection of thunderstorm and hail observation data from the National Meteorological Information Center (NMIC) of China, the hourly and duration datasets which include the onset and end time of thunderstorm and hail were established. Then the characteristics of spatio temporal distribution, duration and their long term trends over Qinghai Province from 1981 to 2011 were documented in this study. The results showed as follows. The frequencies of thunderstorm and hail are significantly influenced by the topography, so both of them occur more frequently in the south part than in the north part over Qinghai Province. Generally speaking, the duration of a thunderstorm process does not last for longer than 40 minutes, and the duration of the hailstorm process does not exceed 10 minutes. The frequencies of thunderstorm and hail both present significant monthly and diurnal variations. In a year, they are mainly concentrated in May to September; in the daytime, they are mainly concentrated in the afternoon, but the occurring time shows an obvious decaying from north to south, and the peak time in the north is about 3 h earlier than in the south part of Qinghai Province. With the duration increasing, the number of thunderstorm processes shows an e folding decay derived from the exponential distribution, while the number of hailstorm processes increases first and then decreases according to the e folding decay. The frequencies of thunderstorm and hail both have presented significant decreasing tendencies since 1981, and the climatic tendencies of thunderstorm and hail are -15.0·(10 a)-1 and -2.3·(10 a)-1, respectively. Although the number of thunderstorm process is decreasing, the average duration of each process shows a slightly increasing trend. And the increasing duration stations are mainly located in the northeastern and central parts of Qinghai, which is the most densely populated area, implying that the potential damage caused by thunderstorm is increasing. Different from that of thunderstorm, the number of hail process and its duration both show decreasing trends, which may be related to the increased height of the melting layer.