中文摘要：

中国北方季风边缘区位置的移动影响着整个西北地区的旱涝变化和生态建设的发展.树轮和历史文献记录可以为该地区过去几百年气候环境变化和季风变化提供重要的信息.本文选取了8条树轮序列结合31条中国历史文献记录和实测降水量资料,重建了中国北方地区近530年的年降水量演化特征,对比分析了不同特征时期400rmm等降水量线空间位置的差异及其可能的驱动机制.结果表明,在年际尺度上,降水量最丰年400mm等降水量线位置都比近30年平均位置偏北,而干旱事件时期400mm等降水量线位置比近30年平均位置更偏南,且干旱时期的波动要比湿润年份的波动幅度更大;在年代际尺度上,最湿润10年和最干旱10年400mm等降水量线位置同样比最近30年偏北和偏南,但是其空间位置的变化没有年际尺度显著.研究区降水量空间位移变化主要是受北大西洋涛动（NAO）和厄尔尼诺南方涛动（ENSO）的影响.

英文摘要：

The spatial change of the fringe of the Asian summer monsoon in Northern China has an important influence on precipitation variations and ecological development. Changes in the strength of the Asian summer monsoon （ASM） have direct impacts on the occurrence of both floods and drought in this zone. This region has an extremely varied climate, ranging from extremely arid to semiarid climate types. Therefore, study of precipitation variations and its possible mechanism in this region is of great importance from both scientific and societal points of view. Tree-ring record is a valuable source of information regarding climate variations and the ASM over several centuries in northern China. Historical documents provide dryness/wetness grade series for 120 locations in China. Taking together, they provide a good basis to study precipitation variability over the last 530 years in northern China. In this paper, we collected newly developed and existing dryness/wetness indices （DWI） for 31 single sites, 8 tree ring-width chronologies and 31 instrumental measurement stations to analyze the precipitation variations in the study region （45°- 33°N, 100°-115°E ） during the period 1470-2000. The missing values of some stations for the DWI were imputed with a Regularized Expectation Maximization （RegEM） algorithm. The instrumental precipitation data spans 1958-2010. The missing values of instrumental data （no more than 3 years） were instead of the average values of the stations. We firstly compared the inter-decadal precipitation variations between historical documentary data and tree-ring width chronologies from 1740A.D. to 2000A.D. It was found that the historical documentary data can effectively represent precipitation variations in study region, so it is appropriate to reconstruct precipitation variations. Then we used ArcGIS 9. 2 geographical software to map the spatial characteristics of 400mm rainfall isoline in severe flooding and drought periods respeetively. An Empirical Orthogonal Function ?