中文摘要：

基于1951-2010年GPCC（Global Precipitation Climatology Centre）的逐月降水数据,利用集合经验模分解法（Ensemble Empirical Mode Decomposition,简称EEMD法）对全球、东西半球、五个大陆和四个典型干旱半干旱区等不同空间尺度年降水量的年代尺度特征进行了研究,区分了不同空间尺度上降水的年代际变化及其长期趋势。结果发现：（1）全球陆地平均降水既存在年代际的周期振荡,又存在长期变化的趋势,降水的年代际周期振荡的强度远大于降水的长期趋势,两者的共同作用使得全球陆地平均降水呈现以年代际周期振荡为主的特征。（2）在半球尺度,2000年以前,东、西半球具有明显相反的年代尺度变化特征,东半球变干（降水减少）,西半球变湿（降水增加）。（3）1951-2010年,欧亚大陆和非洲大陆与北美、南美和澳洲大陆的年代际振荡和趋势存在着一个近似反位相的关系;干旱化与干旱时段是完全不同的两个过程,两者所处的时段也不同;近10年（2001-2010年）全球五个大陆可能将进入一个相对湿润的时段。（4）四个典型干旱半干旱区降水的年代尺度变化具有明显的区域差异。总体来说,华北和北非与北美和中亚降水在长期趋势及年代际振荡上具有反位相的特征。华北和北非的年代际振荡具有近似的位相。在最近几十年,北美和中亚同处于湿润时段,但前者开始于1975年,后者开始于1985年。此外,中亚的第一个湿润时段（1959-1968年）却对应北美的干旱时段。

英文摘要：

Based on 1951-2010 Global Precipitation Climatology Centre monthly precipitation dataset, decadal characteristics of annual precipitation over the globe, the Eastern and Western Hemispheres, five continents and four typical arid and semi-arid regions were analyzed using the Ensemble Empirical Mode Decomposition （EEMD） method. The results showed that： （1） there exists a decadal oscillation in global land precipitation in addition to a long-term trend. Compared to the long-term trend, the decadal oscillation is more distinct and it is the major phenomenon in global land precipitation. （2） On the hemisphere scale, decadal characteristics of the Eastern and Western Hemispheres are opposite before 2000, with a drying trend over the Eastern Hemisphere and an wetting trend over the Western Hemisphere. （3） The decadal oscillation, long-term trend, drying period and drought period of precipitation over Eurasia and Africa exhibit an opposite variation with that over North America, South America and Australia during 1951-2010. Five continents tend to enter a wet phase in the recent 10 years. （4） The decadal characteristics of precipitation over the four typical arid and semi-arid areas have distinctly differences. Generally, the long-term trend and multi-decadal oscillation of precipitation over North China and North Africa are opposite with that over North America and central Asia. North China and North Africa are approximately in phase. Although North America and central Asia are both in wet period in the recent years, the beginning year for the wet period is 1975 in North America and 1985 in central Asia. Additionally, North America experiences a dry period during the first wet period （1959-1968） in central Asia.