中国西北地区1961-2015年干湿程度的区域特征分析

Using monthly observation data from 1961 to 2015 of 116 meteorological stations in northwest China (north of 35 N, west of 115 E), we calculated aridity index (AI) defined by the ratio of precipitation (P) to potential evapotranspiration (PET). According to the result of rotated empirical orthogonal function (REOF) for AI, the Northwest China can be divided into five regions: 1, northern Xinjiang; 2, southern Xinjiang; 3, western Inner Mongolia region; 4, plateau region and 5, eastern of northwest region. Furthermore, we analysed the temporal change characteristics of AI across different regions and determined whether there was breakpoints using Tomé and Miranda's climate trend turning discriminatory model, after that we quantified the individual contributions of every factors to the changes of AI across different regions. The results showed that there were two breakpoints, 1978 and 1993. The "dry-wet-dry" and "dry-wet-slightly wet" pattern were showed in the northern Xinjiang and southern Xinjiang, respectively. Breakpoint was not found in western Inner Mongolia region, it got wetter during 1961-2015 in this region. There are two breakpoints in Plateau region, it was wet during 1961-1985, and then dry during 1985-2000, after 2000 it got wet again. In eastern of northwest region, it was dry before 2000 and then wet after 2000. The characteristics of seasonal change of AI were different with their annual. The precipitation was the most impotant factor in affecting the change of annual and seasonal trend of AI, however other factors also play the important and indispensable roles in their changes.