The Variation of Snow-cover and Snow Disaster in Qinghai During 1961—2004

Using the grid data of 500 hPa height field which is provided by the Natoinal Climate Center and the ground meteorological observation data of seven meteorological stations over the eastern Haixi and around Qinghai Lake (36°~38°N, 96°~101°E) during 1961—2004, the snow disaster's annual table and ground snow sequence is collected, the circulation characteristic of the snow disaster occurred in snowy year and none-snowy year over the eastern Haixi and around Qinghai Lake is analyzed, and based on the climatic diagnosis and the mathematical statistics method the interannual variation characteristic and the generating mechanism as well as the cause of snow disaster are studied. The result shows that the probability of the occurrence of the regional snow disaster over the eastern Haixi and around Qinghai Lake is 15.9% (7/44), while the probability of the occurrence of the local snow disaster is only 9.1% (4/44). Among the eleven snow disasters the probability of snow disaster is 91% (10/11) in later winter to spring (from January to April), and the probability is 9% (1/11) in early winter (from mid October to December). The slowly increasing of the accumulated snow-cover amount over the eastern Haixi and around Qinghai Lake in winter in the 44 years is prone to snow-cover and low temperature damage. The primary influencing system of precipitation over this region is the plateau trough, Mongolia trough and plateau low cyclone (at the same time accompanying convergence line and shearing line), i.e., when the 500 hPa polar vortex center of the north hemisphere from winter to spring is leaning against west/east hemisphere, or the height anomaly of Tibetan Plateau and eastern coast region forms into anomaly distribution with "low in west but high in east (or high in east but low in east)", there has more (only less) snow over the eastern Haixi and around Qing hai Lake. The variation trend of the snow-cover amount in winter and spring in the future 10 years is corresponded with the variation in 1990s, and it also keeps increasing. The snow disasters in later winter to spring over the eastern Haixi and around Qinghai Lake have relationships not only with the local weather and changing climate, but also with the local landform.