Abstract: Based on the data of 170 stations in the area of Shaanxi, Gansu, Ningxia and Qinghai Provinces of northwest China from 1961 to 2008, the regional interconnection and the interannual variability of the atmospheric aridity index were analyzed in this paper. The change trend of regional interconnection and interannual variability was analyzed with method of principal component and rotated principal component. The results show that the large value zone of spatial distribution of annualaridity index in northwest China is consistent with areas from Ningxia to central Gansu, from Dingxi to Longxi, Wushan, Lixian, Wudu and Wenxian, as well as in the dry tongue of the northeast Qinghai-Tibet Plateau. The uniformity of drought and flood abnormities is high in spatial distribution and the first principal component of variance accounts for about 64.6% of the total variance. According to the distribution of loading vector of rotated principal component and their interconnection, three correlative regions of drought and flood abnormities might be approximately divided in the east part of northwest China: the southeast of Gansu and Shaanxi, Gansu corridor and Hetao area, and Qinghai area. In recently 50 years, all region reflected wet and rainy situation during 1974 to 1977 and 1982 to 1985, but dry situation since 1994. The further analysis found that the trend of the climate change shows that the aridity in the east part of northwest China is not an isolated phenomenon. The precipitation is increasing, but the change of the aridity index is unobvious in the Midwest region, which shows the trend of turning wet is unobvious. On the other hand, the change of the aridity index is obvious in the east part, which shows that the trend of turning warming and drying is obvious.

Key words: northwest area of China, EOF, REOF, aridity index, regional teleconnection, annual variation