Study on the Evolution Law of the Extreme Climatic Events over the Source Region of the Three Rivers
三江源地区极端气候事件演变事实及其成因探究

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.