关键词: 三江源地区, 雹灾, 成因

Abstract: Hail disaster is an important natural weather disaster with severe weather in a short time and difficult to forecast，because of complex causes，rapid generation process，small special-scale，and various forming causes in the different regions. The Tibetan Plateau is one of main distribution area of hail disasters in China; one of disaster centers with higher incidence is in the Three-river Headwaters region. Due to the special geographical condition inside the Tibetan Plateau，the formation of hail disasters in Three-river Headwaters region has some differences from the other areas. Based on the official statistics，meteorological data and previous researches，a synthetic database was established of hail disasters in 126 townships of the Three-river Headwaters region during 1950-2011，and the ArcGIS analysis tools were used to analyze the spatial-temporal change of the hail disasters. Correlation analysis was performed among the hail disasters，elevation，precipitation，topographic relief and resident sites density. The conclusions were given as follows：（1）the high-risk centers of hail disasters in the Three-river Headwaters Region include two areas. One is the northeast area with average hail frequency of 26 days a^-1，including Qinghai county，Tongde county，and Guide county. The other one is the south area with average hail frequency of 18 days a^-1，including Chenduo county，Yushu county，and Nangqian county. （2）The frequency of hail disasters increased in recent 60 yrs.，form 3 days a^-1 in 1950s to 15 days a^-1 in 1990s. The hailstorms mainly happen between May and September，and reaching peaks in June and August. （3）The correlation analysis among hail disasters and other natural and social factors shows that the hail disasters of the Three-river Headwaters region have the close relations with altitude，relief of land surface and human activities. The hailstorm frequency has positive correlations with relief degree of land surface and resident sites density，while has negative correlations with altitude. The main influences to spatial variation of hail disasters in the Three- rivers Headwaters region include the shifting of rainband，the different modes of production，and the scale of residents’ activities. The spatial analysis of hail disasters shows the distribution of hail frequencies is different to distribution of hail disasters. The hail disaster center not only relates to hailstorms，but also is determined by the hazard-affected bodies，such as mode of production in this area.

Key words: Three-River Headwaters Region, Hail Disasters, Cause Analysis