西藏冰湖溃决灾害事件极端气候特征

以1960年以来西藏境内已有记载的27次冰湖溃决灾害事件作为研究对象,基于西藏国家气象站点长时间序列（有效记录至今）日气温和日降雨数据,计算得到16个极端气温指数和6个极端降雨指数。通过主成分变换,提取综合极端气温指数和综合极端降雨指数,并进行历史（10年内对比）极端气候特征对比,获得冰湖溃决灾害发生当年及当月极端气候状态,结果表明西藏冰湖溃决灾害发生期（当年及当月）极端气候特征显著,反映极端气候状态对于激发西藏冰湖溃决灾害发生的重要贡献,具体表现为：(1) 67%（18次）的冰湖溃决事件发生当年综合极端气温指数和综合极端降雨指数均大于前期50%年份的综合极端气候指数,其中,13次灾害发生当年极端气候异常水平超过前期70%年份;(2)已有灾害暴发月份记载的25次冰湖溃决事件中,19次冰湖溃决事件发生当月极端气候指数异常偏高,11次冰湖溃决事件发生当月极端气温和极端降水均大于75%往年同期综合极端气候指数;(3)部分灾害事件如扎日错（1981年6月)、龙纠错溃决（2000年8月）等,灾害发生当年极端气温状态低于往年,而暴发当月综合极端气温指数和综合极端降雨指数均大于历史同期水平,表现为加剧状态;(4)所有冰湖溃决灾害发生当月的综合极端气温指数均高于往年同期指数,表明短历时极端气温事件对高原冰湖溃决灾害形成具有重要影响。

The extreme climate background for glacial lakes outburst flood events in Tibet

In order to clearly understand the extreme climate background at the time of glacial lake outburst flood (GLOF) occurrence in high altitude mountain, we took 27 GLOF events recorded in Tibet since 1960 as samples. Based on the daily temperature data and the daily precipitation data recorded by these meteorological stations in the vicinity of the places where GLOF events occurred, 16 temperature extremes indices and 6 precipitation extremes indices were calculated in these places. By the method of Principal Component Analysis (PCA), a comprehensive extreme temperature index and a comprehensive extreme precipitation index were extracted, and the fluctuation of extreme climate in this period when the disaster occurred were obtained by compared the value of the comprehensive extreme climate index of the previous nine years on annual scale and monthly scale, respectively. The results showed that: (1) More frequent extreme temperature events and precipitation events appeared in the year when GLOF occurred by compared with the previous nine years on annual scale, which was validated in about 67% of GLOF events. (2) Among the 25 GLOF events with monthly outbreak time record, the monthly extreme temperature index and the monthly extreme precipitation index when disaster occurrence were more than 75% of that in the same period of previous nine years, which was validated in about 11 GLOF events. (3) The extreme climate events in several years when GLOF occurred were not very frequent, while both of the extreme temperature index and the extreme precipitation index on monthly scale were obviously higher than the same period of previous nine years, such as Zharicuo GLOF (June 1981), Longjiucuo GLOF (August 2000), Degacuo GLOF (September 2002), Ranzeria GLOF (July 2013) and the nameless lake (July 2015). (4) The monthly extreme temperature index of all GLOF events was higher than that of the same period of the previous nine years, which shows that the short-term extreme temperature events have an important impact on the formation of GLOF in high altitude mountain.