摘要:
基于历史文献记录，运用REOF分析方法将西北地区1470~2008 AD干湿序列分解为空间函数和时间函数，用前6个主要空间特征向量描述西北地区干湿变化的空间格局，构建区域干湿指数(RDWI)，表征区域干湿变化的程度及差异。研究发现：1) 西北地区降水量分布场大致以105˚E为界呈现东湿西干的格局，湿极出现在陕南，而玉树则是旱极。2) 1470~2008年西北地区干旱年份有41年，偏干79年，正常年份有285年，偏湿年份95年，湿润年份39年。极端干旱年份有1484，1528，1586，1640，1759，1877，1878，1928，1900，1915，1929；极端湿润年份有1570，1662，1736，1745，1753，1756，1819，1884，1887，1958，1964。3) RDWI数据序列11点低通滤波表明西北地区1470~2008年干湿年代际波动变化特征极为复杂，主要存在8个干湿变化旋回。其中1481~1497，1527~1531，1583~1588，1628~1642，1713~1722，1874~1879，1915~1931年为连续干旱时段。4) 采用小波与连续功率谱分析发现西北地区1470~2008年间存在着64~90年、32~48和11~22年左右的3类周期变化规律。检测出的64年的周期以及未检测出200年的周期与已有研究不同。
Abstract:
Based on the historical record, the REOF method was used to decompose the dry/wet variation in northwest China from 1470 to 2008 into spatial functions and time functions; the spatial pattern of dry/wet differences was described by the first six major space feature vectors; Regional Dry-Wet Index (RDWI) by the corresponding time weighting coefficient was used to represent the time changes of spatial differences. Several important conclusions were found in this paper. First, distribution of dry/wet variation field in northwest China was the dividing line of 105˚E. Southern Shaanxi is the wettest place and Yushu is the driest place in the west of 105˚E. Secondly, 41 years were very dry in northwest China from 1470 to 2008, and there were 79 dry years, 285 normal years, 95 wet years, and 39 very wet years. Among them, extreme dry years are in 1484, 1528, 1586, 1640, 1759, 1877, 1878, 1928, 1900, 1915 and 1929; extreme wet years are in 1570, 1662, 1736, 1745, 1753, 1756, 1819, 1884, 1887, 1958 and 1964. Thirdly, after 11-point low-pass filter, RDWI data sequence shows that dry-wet decadal fluctuations’ change characteristic is very complex, and there are eight climate change cycles. 1481-1497, 1527-1531, 1583-1588, 1628-1642, 1713-1722, 1874-1879, 1915-1931 years are the persistent dry periods. Last but not least, wavelet and power spectrum analysis shows that some periodicities existed in the last 500 years, such as the periods of around 64 - 90, 32 - 48 and 11 - 22 years. Among them, the detected 64-year periodicity and the not detected 200-year periodicity are different from the existing research.