1961—2010年西藏极端降水事件时空分布特征

Temporal and Spatial Distribution of Extreme Precipitation Events in Tibet during 1961—2010

利用1961～2010年西藏自治区21个气象观测站逐日降水量，采用基于百分位的相对指数法定义极端事件，并利用统计方法分析了西藏极端降水事件的时空变化特征，包括极端降水阈值、频数、强度的空间变化特征，以及极端降水强度及频数的线性变化趋势及周期特征。结果表明，西藏极端降水事件阈值在15．7～36．0mm之间，极端降水阈值和强度的高值区均位于西藏南部边缘地区的聂拉木、沿江中段的日喀则以及东南部的波密和察隅一带；极端降水事件出现频数在17～108天之间，主要呈经向分布特征，自东向西逐渐减少；在时间上，1961—201D年间西藏西部、北部和东南部极端降水事件出现频数呈减少趋势，其中西部与东南部频数减小趋势较为明显；沿雅鲁藏布江一线、西藏南部和东北部极端降水事件出现频数呈增多趋势；西藏各地极端降水事件频数存在准3年周期，西部和南部一线还存在准8年周期。

The extreme precipitation event （EPE） in the Tibet Plateau is defined by relative index method and its spatial-temporal characteristics and period are analyzed by indicators including threshold, frequency, and intensi- ty based on the daily rainfall data in 21 meteorological.stations during 1961 --2010. The results show that the threshold of EPE in Tibet Plateau ranges 15.7 -36.0 mm, and Nielamu in the south, Rikaze in the valley of the Yarlung Zangbo River and Bomi and Chayu in southeast of Tibet Plateau have higher EPE threshold and intensi- ty. Frequency of EPE is between 17 - 108 d, and its distribution has the reducing trend from east to west part of Tibet. During 1961 --2010, a decreasing trend can be found in the west, north and southeast regions of Tibet, and such trend is more notable in west and southeast of Tibet. Frequency of EPE shows increasing trend in south, northeast of Tibet and the valley of the Yarlung Zangbo River. There are 3 years period of the frequency all over Tibet, and 8 years in west and south of Tibet.