近30年西藏汛期强降水事件的时空变化特征

利用1980-2008年汛期(5～9月)西藏38个气象站逐日降水量资料,定义了西藏强降水标准,并采用REOF、SSA等统计方法,分析了汛期强降水发生频次的时空分布特征。结果表明,西藏地区汛期强降水发生频数自东南向西北逐渐减少,但总体呈不明显的增多趋势,即从20世纪80年代中期开始减少,90年代中期降至最少,之后逐渐增多;频数存在5个异常分布空间型,即南部型、沿江型、东部型、北部型和东南部型。各空间型的强降水发生频数随时间变化均不同,其中南部型、东南部型表现为减少趋势;沿江型、东部型和北部型表现为增多趋势。汛期强降水发生频数的准2～3年和准5～6年周期在5个异常空间型普遍存在。

Temporal-Spatial Distributions of Severe Precipitation Event during Flood Period in Tibet in Last 30 Years

Using the daily precipitation data from 38 obseration stations in Tibet during the flood period(from May to September) in 1980-2008,the standard of severe precipitation event is defined and the temporal-spatial distributions of severe precipitation frequency based on REOF,SSA and so on.The results show that the frequency of severe precipitation event decreases from southeast to northwest during the flood period,in general it increases slightly,which decreases in the middle of 1980s,the most significant in the middle of 1990s,then gradually increases.The severe precipitation event has five anomalous spatial patterns in Tibet,such as south pattern,Yarlungzangbo pattern,east pattern,north pattern and southeast pattern.The change of severe precipitation frequency in each spatial pattern with time is different.South pattern and southeast pattern appear the decreasing trend,and other three patterns appear the increasing trend.The singular spectrum analysis shows that 2~3 and 5~6 year periods exist among all of 5 patterns for the frequency of severe precipitation event during the flood period in Tibet.