西藏高原降水变化趋势的气候分析

利用西藏1971~2000年月降水量、降水日数资料,分析了近30年高原降水的变化趋势。结果发现,西藏大部分地区年降水量变化为正趋势,降水倾向率为1.4~66.6 mm/10a,而阿里地区呈较为明显的减少趋势。年降水日数变化阿里地区、林芝地区东部为负趋势,正趋势以那曲地区中西部、昌都地区北部最为明显。20世纪70年代高原西部为正距平、东部为负距平,20世纪80年代大部分地区为负距平,20世纪90年代高原西部为负距平,东部为正距平。近30年来西藏高原平均年、四季降水量均呈增加趋势,年降水量以19.9 mm/10a的速率增加,尤其是20世纪90年代增幅较大,1992年以来春、夏季降水明显增加。阿里地区出现了暖干化趋势。年降水异常偏涝年主要出现在20世纪80和90年代。

Climatic Trend of Rainfall over Tibetan Plateau from 1971 to 2000

Using the data of monthly rainfall and rainy days from 1971 to 2000 in Tibet, the linear trends of the annual and seasonal rainfall and rainy days are analyzed. The results show that, the annual rainfall trend in most parts of Tibet increased, rainfall trend was 1.4-66.6 mm/10a, and the change trend of rainfall decreased in Ngari district. A decline trend of rainy days (R≥0.1) was found over Ngari and eastern Nyingchi districts, the increase of rainy days was obvious in middle-western Nagqu and northern Qamdo districts. In the 1970s, the precipitation positive anomaly occurred in western Tibet, and negative anomaly in eastern Tibet. The precipitation anomaly is negative in most parts of Tibet in the 1980s. For precipitation anomaly in the 1990s, the positive appeared in eastern Tibet and the negative in western Tibet. It was also found that change trend of mean annual and seasonal rainfall of Tibet increased during the 30 years, and annual rainfall trend indicated an increase of 19.9 mm/10a, especially in the 1990s. After 1992, the rainfall increased during spring and summer.