1470-1912年西北东部地区旱涝等级重建序列的特征及对比分析

Characteristics and comparative analysis of reconstructed drought/flood grade sequence in the eastern Northwest China from 1470 to 1912

通过收集整理西北地区东部1470-1912年旱涝灾害历史文献资料,重新建立逐年旱涝等级序列。利用滑动平均、累计距平、滑动T检验和小波变换等方法,综合分析了443 a间西北东部地区旱涝序列的变化特征。为验证本序列的可靠性,利用华山降水量重建序列和陇西地区干湿指数序列进行长期趋势对比分析,并将代表性省份石笋δ18O序列和重建旱涝等级序列进行对比验证。结果表明：（1）西北东部地区以旱灾为主,旱灾频繁且大旱、连旱严重。旱涝灾害具有明显的阶段性,大致可分为4个阶段,分别为1470-1540年、1541-1615年、1616-1796年和1797-1912年,且可分为12个明显的偏旱和偏涝时期。（2）在10 a尺度上检测出旱涝变化存在12个突变点,50 a尺度上存在5个突变点。（3）重建序列存在较明显的周期变化的时间尺度是130-110 a、70-80 a、50-52 a和28 a、10-15 a、5 a。28 a左右时的周期振荡最强,为第1主周期,第2、3、4周期依次是15 a、73 a和50 a。（4）根据对比分析,早涝重建序列和其他长降水量序列具有较高的一致性,与同期石笋氧同位素δ18O记录对应较好,间接证明了历史文献资料恢复历史时期气候变化的可靠性和可行性。

In recent years, under the background of global climate anomalies, drought and flood disasters occurred frequently in China. The historical climate research is an important content of international Climate Variability and Predictability Program. In recent decades, some scientists had made great progress in reconstructing the sequences of drought and flood based on historical documentary files, however, most of these rebuild sequences of drought and flood were mainly concentrated in Eastern China. Due to lack of early data, there were few research and analysis of historical flood and drought in northwest China. Collecting and classifying the data of drought and flood disasters in the eastern Northwest China from 1470 to 1912, and according to the criterion of drought and flood grade, this paper reconstructed the sequence of drought and flood grade. The change characteristics of drought and flood disasters including the decade and century frequency, periodic and mutability, periodicity over the past 443 years in all the regions were analyzed by using the moving average, accumulative anomaly, moving t-test technique, and wavelet analysis. Finally, in order to test and verify the reliability of this sequence, regional long-term trend was analyzed by comparing the Huashan precipitation reconstructed sequences and D/F index in Longxi, and further compared drought and flood grade curve with the stable oxygen isotopic record both from typical provinces. Results showed that drought disasters took place frequently and seriously in the eastern Northwest China. The alternate phenomenon about drought and flood was obvious. Probability of drought and the partial drought were higher than flood disasters, and the probability of flood years was the lowest. The drought and flood disaster which had obvious phases features could be divided into four stages： 1470-1540, 1541-1615, 1616-1796 and 1797-1912. Based on the four stages, we could further divide them into twelve drought-partial or flood-partial periods. Using moving t-test technique, we found that there were 12 abrupt changes on decade scale and 5 abrupt changes on 50 years scale. The reconstructed sequences displayed a periodic variability in multiple scales, which were comparatively obvious on the timescale of 130-110 a, 70-80 a, 50-52 a and 28 a, 10-15 a, 5 a, especially on the timescale of 10-15 a and 28 a. The first four periodic oscillations, from high to low, were in 28 a, 15 a, 73 a and 5 a. According to the comparison analysis, reconstruction of drought and flood grade sequence has high consistency with other precipitation sequence, showing multiple similar trends that peaks and troughs appeared at the same time, and corresponds to stalagmites oxygen isotopes records during the same period. All these could be an indirect proof of reliability and feasibility of our recovered historical flood and drought grade sequence based on the historical document data. The results have important practical significance for the development of disaster prevention and mitigation measures in eastern Northwest China. The study will be very important to discover the changing rules of drought and flood disaster and make accurately forecast for the future climate.