三江源地区极端气候事件演变事实及其成因探究

利用三江源地区14个气象台站1962-2005年逐日气温、降水资料分析了该地区冷暖干湿极端气候事件的演变规律，探讨了其变化成因。研究表明：近44a来三江源地区气温等级由冷向暖转变，极端高温事件频繁发生，而极端低温事件则逐年减少，致使气温不断向着更高的均值状态持续增暖；尽管降水量干湿变化不甚显著，但降水的极端状况即严重干旱或暴雨事件均呈减少趋势，降水量的变化趋于稳定，降水变率减小；地形对极端气温、降水事件频次变幅的空间分布均有着较为显著的影响，且对后者的影响更为显著；高原季风、厄尔尼诺事件及高原积雪等因子的年际振荡是三江源地区极端气候事件发生频次波动的主要原因。

Study on the Evolution Law of the Extreme Climatic Events over the Source Region of the Three Rivers

Based on the day by day air temperature and rainfall data of 14 weather stations over the source region of the three rivers(Yangtze,Yellow and Lancangjiang rivers),the evolution law of the extreme cold,warm,dry and wet climatic events as well as cause of its variations are analyzed.The result shows that the air temperature grade over the source region of the three rivers has changed from cold to warm state in recent 44 years,the extreme high temperature event has been happening frequently,while the extreme low temperature event shows a decreasing trend year affer year,therefore this makes air temperature keep rising to the higher averaged state.Although the dry and wet variation of precipitation is not so evident,the extreme event of severe drought or the rainstorm both appears a decreasing trend,the variation of precipitation tends to be stable,and its variability gets decreasing.The topography has a significant impact on the spatial distribution of extreme air temperature and precipitation frequency,especially more significant on the latter.The interannual oscillations of plateau monsoon,El Nino event and plateau snow cover are the main reasons for the variations of occurring frequency of the extreme climatic events over the source region of the three rivers.