西安地区(380—1983年)旱涝气候变化

CLIMATIC CHANGES OF DROUGHT-WET IN XIAN REGION OF CHINA DURING THE LAST 1604 YEARS

依据历史记载,采用最优分割法、功率谱分析及谐波分析等方法,建立西安(古长安)地区近1604年的旱涝指数气候序列,探讨该地区旱涝气候特征及旱涝变化规律,并与相邻地区作了对比。

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 昽n atmospheric circulation.