关键词: 旱涝变化, 西安

Abstract: According to the historic records of Xian region, a climatic series of drought-wet indices of this region for the last 1604 years was reconstructed.By method of optimum classification (classifying by statistic variances), power spectrum analysis, and harmonic analysis, some characteristics of the drought-wet climate in Xian and its relationships with those in other places on the northern hemisphere were explored.The climatic change of drought-rainfall in Xian can be divided into six periods.Ⅰ.380-680 A.D., dry.Ⅱ.690-990, wet.Ⅲ.1000-1220, dry.Ⅳ.1230-1410, wet.Ⅴ.1420-1630, dry.Ⅵ.1640-now, wet.On the secondary time scale of about a century, the drought-wet climate in Xian may be divided into 18 episodes, each of which ranged about 89 years on average.There were three rather dry episodes respectively in 460-500, 1140-1220, 1420-1490, and several wet episodes appeared in 690-750, 1230-1250, 1380-1410, 1640-170., 1810-now.Since 380 A.D.the duration of the dry periods has become shorter and the latest wet period of these two time scales are the longest of all.By calculating the ratio of dry or wet years during each period, we discovered that even in the, wet periods in Xian, dry years still occurred frequently.The result of hammonic analysis to the drought-rainfall series, climate in Xian varied, on the background of changing with the period of about 520 years, with the notable periods of 71-75 years.The statistical correlations of the wet/dry climatic indices series between Xian and other places show results similar to those obtained from the study on atmospheric circulation.

Key words: Changes of drought-wet, Xian region